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Label Element Value
Prospectus [Line Items] rr_ProspectusLineItems  
Document Type dei_DocumentType 485BPOS
Document Period End Date dei_DocumentPeriodEndDate Sep. 30, 2021
Entity Registrant Name dei_EntityRegistrantName THORNBURG INVESTMENT TRUST
Entity Central Index Key dei_EntityCentralIndexKey 0000816153
Entity Inv Company Type dei_EntityInvCompanyType N-1A
Amendment Flag dei_AmendmentFlag false
Document Creation Date dei_DocumentCreationDate Jan. 28, 2022
Document Effective Date dei_DocumentEffectiveDate Feb. 01, 2022
Prospectus Date rr_ProspectusDate Feb. 01, 2022
Retail | Thornburg Global Opportunities Fund  
Prospectus [Line Items] rr_ProspectusLineItems  
Risk/Return [Heading] rr_RiskReturnHeading Global Opportunities Fund
Objective [Heading] rr_ObjectiveHeading Investment Goal
Objective, Primary [Text Block] rr_ObjectivePrimaryTextBlock

The Fund seeks long-term capital appreciation by investing in equity and debt securities of all types from issuers around the world.
Expense [Heading] rr_ExpenseHeading Fees and Expenses of the Fund
Expense Narrative [Text Block] rr_ExpenseNarrativeTextBlock

This table describes the fees and expenses that you may pay if you buy and hold shares of the Fund. You may qualify for discounts from the sales charges applicable to Class A shares if you or other qualifying account holders invest, or agree to invest in the future, at least $50,000 in the Thornburg Funds. More information about this and other discounts and sales charge waivers is available from your financial intermediary, in the Prospectus under the captions “Class A Sales Charge Waivers,” beginning on page 146, and “Appendix A – Sales Charge Waivers Offered by Financial Intermediaries,” beginning on page 200, and in the Statement of Additional Information under the caption “Additional Information Respecting Purchase and Redemption of Shares,” beginning on page 108.
Shareholder Fees Caption [Text] rr_ShareholderFeesCaption Shareholder Fees (fees paid directly from your investment)
Operating Expenses Caption [Text] rr_OperatingExpensesCaption Annual Fund Operating Expenses (expenses that you pay each year as a percentage of the value of your investment)
Fee Waiver or Reimbursement over Assets, Date of Termination rr_FeeWaiverOrReimbursementOverAssetsDateOfTermination February 1, 2023
Portfolio Turnover [Heading] rr_PortfolioTurnoverHeading Portfolio Turnover.
Portfolio Turnover [Text Block] rr_PortfolioTurnoverTextBlock

The Fund pays transaction costs, such as commissions, when it buys and sells securities (or “turns over”) its portfolio. A higher portfolio turnover rate may indicate higher transaction costs and may result in higher taxes when Fund shares are held in a taxable account. These costs, which are not reflected in Annual Fund Operating Expenses or in the Example, affect the Fund’s performance. During the most recent fiscal year, the Fund’s portfolio turnover rate was 25.48% of the average value of its portfolio.
Portfolio Turnover, Rate rr_PortfolioTurnoverRate 25.48%
Expense Breakpoint Discounts [Text] rr_ExpenseBreakpointDiscounts You may qualify for discounts from the sales charges applicable to Class A shares if you or other qualifying account holders invest, or agree to invest in the future, at least $50,000 in the Thornburg Funds.
Expense Breakpoint, Minimum Investment Required [Amount] rr_ExpenseBreakpointMinimumInvestmentRequiredAmount $ 50,000
Expense Example [Heading] rr_ExpenseExampleHeading Example.
Expense Example Narrative [Text Block] rr_ExpenseExampleNarrativeTextBlock

This Example is intended to help you compare the cost of investing in the Fund with the cost of investing in other mutual funds.

The Example assumes that you invest $10,000 in the Fund for the time periods indicated and then redeem all of your shares at the end of those periods. The Example also assumes that your investment has a 5% return each year, dividends and distributions are reinvested, and that the Fund’s operating expenses remain the same. Although your actual costs may be higher or lower, based on these assumptions (and giving effect to fee waivers and expense reimbursements in the first year), your costs would be:
Expense Example, No Redemption Narrative [Text Block] rr_ExpenseExampleNoRedemptionNarrativeTextBlock

You would pay the following expenses if you did not redeem your Class C shares:
Strategy [Heading] rr_StrategyHeading Principal Investment Strategies
Strategy Narrative [Text Block] rr_StrategyNarrativeTextBlock

The Fund pursues its investment goal by investing primarily in a broad range of equity securities, including common stocks, preferred stocks and publicly traded real estate investment trusts. The Fund may invest in any stock or other equity security which its investment advisor, Thornburg Investment Management, Inc. (“Thornburg”), believes may assist the Fund in pursuing its goal, including smaller companies with market capitalizations less than $500 million.

The Fund portfolio includes investments in both domestic securities and securities of issuers domiciled in or economically tied to countries outside the United States, including developing countries. Relative proportions of each will vary from time to time, depending upon the advisor’s view of specific investment opportunities and macro-economic factors. Under normal market conditions, the Fund invests a significant portion of its assets in issuers domiciled in or economically tied to countries outside the United States.

The Fund’s investments are determined by individual issuer and industry analysis. Investment decisions are based on domestic and international economic developments, outlooks for securities markets, interest rates and inflation, the supply and demand for securities, and analysis of specific issuers.

The Fund may sell an investment if Thornburg has identified a better investment opportunity, in response to changes in the conditions or business of the investment’s issuer or changes in overall market conditions, if Thornburg has a target price for the investment and that target price has been achieved, or if, in Thornburg’s opinion, the investment no longer serves to achieve the Fund’s investment goals.
Risk [Heading] rr_RiskHeading Principal Investment Risks
Risk Narrative [Text Block] rr_RiskNarrativeTextBlock

An investment in the Fund is not a deposit in any bank and is not insured or guaranteed by the Federal Deposit Insurance Corporation or any other governmental agency. Accordingly, the loss of money is a risk of investing in the Fund. The value of the Fund’s shares varies from day to day and over time, and when you sell your shares they may be worth less than what you paid for them. The following is a summary of the principal risks of investing in the Fund.

Management Risk – The Fund is an actively managed portfolio, and the value of the Fund may be reduced if Thornburg pursues unsuccessful investments or fails to correctly identify risks affecting the broad economy or specific issuers in which the Fund invests.

Market and Economic Risk – The value of the Fund’s investments may decline and its share value may be reduced due to changes in general economic and market conditions. The value of a security may change in response to developments affecting entire economies, markets or industries, including changes in interest rates, political and legal developments, and general market volatility.

Equity Risk – The value of the Fund’s equity investments may fluctuate significantly over time in response to factors affecting individual issuers, particular industries, or the market as a whole. Additionally, common stock ranks below preferred stock and debt securities in claims for dividends and for assets of a company in a liquidation or bankruptcy.

Risks Affecting Specific Issuers – The value of a security may decline in response to developments affecting the specific issuer of the security, even if the overall industry or economy is unaffected. These developments may include a variety of factors, including but not limited to management issues or other corporate disruption, a decline in revenues or profitability, an increase in costs, or an adverse effect on the issuer’s competitive position.

Foreign Investment Risk – Investments in securities of foreign issuers may involve risks including adverse fluctuations in currency exchange rates, political instability, confiscations, taxes or restrictions on currency exchange, difficulty in selling foreign investments, and reduced legal protection.

Developing Country Risk – The risks which may affect investments in foreign issuers (see “Foreign Investment Risk,” above) may be more pronounced for investments in developing countries because the economies of those countries are usually less diversified, communications, transportation and economic infrastructures are less developed, and developing countries ordinarily have less established legal, political, business and social frameworks. At times the prices of equity securities of a developing country issuer may be extremely volatile. An issuer domiciled in a developed country may be similarly affected by these developing country risks to the extent that the issuer conducts its business in developing countries.

Foreign Currency Risk – Fluctuations in currency exchange rates can adversely affect the value of the Fund’s foreign investments. Such fluctuations may occur for a number of reasons, including market and economic conditions, or a government’s decision to devalue its currency or impose currency controls.

Risks Affecting Specific Countries or Regions – If a significant portion of the Fund’s assets is invested in issuers that are economically exposed to one country or region, the Fund’s share value may be more susceptible to the conditions and developments in that country or region, and potentially more volatile than the share value of a more geographically diversified fund. A specific country or region could also be adversely affected by conditions or developments arising in other countries. For example, the U.S. government could take actions to prohibit or restrict individuals or companies within the U.S. from purchasing or holding the shares of issuers in another country, which may limit the Fund’s ability to invest in that country or cause the Fund to have to sell investments in that country at less than desired prices. The nature and degree of the risks affecting a given country or region, and the extent of the Fund’s exposure to any such country or region, is expected to vary over time.

Small and Mid-Cap Company Risk – Investments in small-capitalization companies and mid-capitalization companies may involve additional risks, which may be relatively higher with smaller companies. These additional risks may result from limited product lines, more limited access to markets and financial resources, greater vulnerability to competition and changes in markets, lack of management depth, increased volatility in share price, and possible difficulties in valuing or selling these investments.

Credit Risk – The inability of an issuer to pay principal and interest on its debt obligations when due, or the downgrading of an issuer’s debt obligations by ratings agencies, may adversely affect the market’s perceptions of the issuer’s financial strength and may therefore result in declines in the issuer’s stock price.

Liquidity Risk – Due to a lack of demand in the marketplace or other factors, the Fund may not be able to sell some or all of its investments promptly, or may only be able to sell investments at less than desired prices. This risk may be more pronounced for the Fund’s investments in developing countries.

Real Estate Risk – The Fund’s investments in publicly traded real estate investment trusts (“REITs”) are subject to risks affecting real estate investments generally (including market conditions, competition, property obsolescence, changes in interest rates and casualty to real estate), as well as risks specifically affecting REITs (the quality and skill of REIT management and the internal expenses of the REIT).

Cybersecurity and Operational Risk – Operational failures, cyber-attacks or other disruptions that affect the Fund’s service providers, the Fund’s counterparties, other market participants or the issuers of securities held by the Fund may adversely affect the Fund and its shareholders, including by causing losses for the Fund or impairing Fund operations.

Additional information about Fund investments, investment strategies and risks of investing in the Fund appears beginning on page 118 of the Prospectus.
Risk Lose Money [Text] rr_RiskLoseMoney Accordingly, the loss of money is a risk of investing in the Fund.
RIsk Not Insured [Text] rr_RiskNotInsured An investment in the Fund is not a deposit in any bank and is not insured or guaranteed by the Federal Deposit Insurance Corporation or any other governmental agency.
Bar Chart and Performance Table [Heading] rr_BarChartAndPerformanceTableHeading Past Performance of the Fund
Performance Narrative [Text Block] rr_PerformanceNarrativeTextBlock

The following information provides some indication of the risks of investing in Global Opportunities Fund by showing how the Fund’s investment results vary from year to year. The bar chart shows how the annual total returns for Class A shares have been different in each full year shown. The average annual total return figures compare Class A, Class C and Class I share performance to the MSCI ACWI Net Total Return USD Index, which represents a broad measure of both domestic and foreign equity market performance. Past performance (before and after taxes) is not necessarily an indication of how the Fund will perform in the future. The performance information shown is as of the calendar year ended December 31, 2021. Updated performance information may be obtained on the Thornburg website at Thornburg.com or by calling 1-800-847-0200.
Performance Information Illustrates Variability of Returns [Text] rr_PerformanceInformationIllustratesVariabilityOfReturns The following information provides some indication of the risks of investing in Global Opportunities Fund by showing how the Fund’s investment results vary from year to year.
Performance Availability Phone [Text] rr_PerformanceAvailabilityPhone 1-800-847-0200
Performance Availability Website Address [Text] rr_PerformanceAvailabilityWebSiteAddress Thornburg.com
Performance Past Does Not Indicate Future [Text] rr_PerformancePastDoesNotIndicateFuture Past performance (before and after taxes) is not necessarily an indication of how the Fund will perform in the future.
Bar Chart [Heading] rr_BarChartHeading Annual Total Returns – Class A Shares
Bar Chart Does Not Reflect Sales Loads [Text] rr_BarChartDoesNotReflectSalesLoads The sales charge for Class A shares is not reflected in the returns shown on the bar chart, and the returns would be less if the charge was taken into account.
Bar Chart Closing [Text Block] rr_BarChartClosingTextBlock

Total
Returns

Quarter
ended

Highest Quarterly Results

21.72%

6/30/2020

Lowest Quarterly Results

(24.82)%

3/31/2020

The sales charge for Class A shares is not reflected in the returns shown on the bar chart, and the returns would be less if the charge was taken into account.
Performance Table Heading rr_PerformanceTableHeading Average Annual Total Returns (periods ended 12-31-21)
Performance Table Uses Highest Federal Rate rr_PerformanceTableUsesHighestFederalRate After-tax returns are calculated using the highest historical individual federal marginal income tax rates, and do not reflect state or local income taxes.
Performance Table Not Relevant to Tax Deferred rr_PerformanceTableNotRelevantToTaxDeferred Actual after-tax returns depend on an investor’s own tax situation and may differ from the returns shown, and after-tax returns shown are not relevant to investors who hold their Fund shares through tax-deferred arrangements, such as 401(k) plans or individual retirement accounts.
Performance Table One Class of after Tax Shown [Text] rr_PerformanceTableOneClassOfAfterTaxShown The after-tax returns shown relate only to Class A shares, and after-tax returns for other share classes will vary.
Performance Table Closing [Text Block] rr_PerformanceTableClosingTextBlock

After-tax returns are calculated using the highest historical individual federal marginal income tax rates, and do not reflect state or local income taxes. Actual after-tax returns depend on an investor’s own tax situation and may differ from the returns shown, and after-tax returns shown are not relevant to investors who hold their Fund shares through tax-deferred arrangements, such as 401(k) plans or individual retirement accounts. The after-tax returns shown relate only to Class A shares, and after-tax returns for other share classes will vary.
Retail | Thornburg Global Opportunities Fund | Thornburg Global Opportunities Fund - Class A  
Prospectus [Line Items] rr_ProspectusLineItems  
Trading Symbol dei_TradingSymbol THOAX
Maximum Sales Charge Imposed on Purchases (as a percentage of Offering Price) rr_MaximumSalesChargeImposedOnPurchasesOverOfferingPrice 4.50%
Maximum Deferred Sales Charge (as a percentage) rr_MaximumDeferredSalesChargeOverOther none [1]
Management Fees (as a percentage of Assets) rr_ManagementFeesOverAssets 0.85%
Distribution and Service (12b-1) Fees rr_DistributionAndService12b1FeesOverAssets 0.25%
Other Expenses (as a percentage of Assets): rr_OtherExpensesOverAssets 0.21%
Expenses (as a percentage of Assets) rr_ExpensesOverAssets 1.31%
Fee Waiver or Reimbursement rr_FeeWaiverOrReimbursementOverAssets
Net Expenses (as a percentage of Assets) rr_NetExpensesOverAssets 1.31%
Expense Example, with Redemption, 1 Year rr_ExpenseExampleYear01 $ 577
Expense Example, with Redemption, 3 Years rr_ExpenseExampleYear03 847
Expense Example, with Redemption, 5 Years rr_ExpenseExampleYear05 1,136
Expense Example, with Redemption, 10 Years rr_ExpenseExampleYear10 $ 1,958
Annual Return 2012 rr_AnnualReturn2012 21.56%
Annual Return 2013 rr_AnnualReturn2013 28.18%
Annual Return 2014 rr_AnnualReturn2014 18.44%
Annual Return 2015 rr_AnnualReturn2015 1.12%
Annual Return 2016 rr_AnnualReturn2016 3.64%
Annual Return 2017 rr_AnnualReturn2017 21.64%
Annual Return 2018 rr_AnnualReturn2018 (20.92%)
Annual Return 2019 rr_AnnualReturn2019 28.35%
Annual Return 2020 rr_AnnualReturn2020 22.32%
Annual Return 2021 rr_AnnualReturn2021 14.42%
Highest Quarterly Return, Label rr_HighestQuarterlyReturnLabel Highest Quarterly Results
Highest Quarterly Return, Date rr_BarChartHighestQuarterlyReturnDate Jun. 30, 2020
Highest Quarterly Return rr_BarChartHighestQuarterlyReturn 21.72%
Lowest Quarterly Return, Label rr_LowestQuarterlyReturnLabel Lowest Quarterly Results
Lowest Quarterly Return, Date rr_BarChartLowestQuarterlyReturnDate Mar. 31, 2020
Lowest Quarterly Return rr_BarChartLowestQuarterlyReturn (24.82%)
1 Year rr_AverageAnnualReturnYear01 9.25%
5 Years rr_AverageAnnualReturnYear05 10.54%
10 Years rr_AverageAnnualReturnYear10 12.31%
Retail | Thornburg Global Opportunities Fund | Thornburg Global Opportunities Fund - Class A | After Taxes on Distributions  
Prospectus [Line Items] rr_ProspectusLineItems  
1 Year rr_AverageAnnualReturnYear01 5.72%
5 Years rr_AverageAnnualReturnYear05 9.07%
10 Years rr_AverageAnnualReturnYear10 11.47%
Retail | Thornburg Global Opportunities Fund | Thornburg Global Opportunities Fund - Class A | After Taxes on Distributions and Sales  
Prospectus [Line Items] rr_ProspectusLineItems  
1 Year rr_AverageAnnualReturnYear01 7.53%
5 Years rr_AverageAnnualReturnYear05 8.01%
10 Years rr_AverageAnnualReturnYear10 10.05%
Retail | Thornburg Global Opportunities Fund | Thornburg Global Opportunities Fund - Class A | MSCI ACWI Net Total Return USD Index (reflects no deduction for fees, expenses, or U.S. taxes)  
Prospectus [Line Items] rr_ProspectusLineItems  
1 Year rr_AverageAnnualReturnYear01 18.54%
5 Years rr_AverageAnnualReturnYear05 14.40%
10 Years rr_AverageAnnualReturnYear10 11.85%
Retail | Thornburg Global Opportunities Fund | Thornburg Global Opportunities Fund - Class C  
Prospectus [Line Items] rr_ProspectusLineItems  
Trading Symbol dei_TradingSymbol THOCX
Maximum Sales Charge Imposed on Purchases (as a percentage of Offering Price) rr_MaximumSalesChargeImposedOnPurchasesOverOfferingPrice none
Maximum Deferred Sales Charge (as a percentage) rr_MaximumDeferredSalesChargeOverOther 1.00% [2]
Management Fees (as a percentage of Assets) rr_ManagementFeesOverAssets 0.85%
Distribution and Service (12b-1) Fees rr_DistributionAndService12b1FeesOverAssets 1.00%
Other Expenses (as a percentage of Assets): rr_OtherExpensesOverAssets 0.23%
Expenses (as a percentage of Assets) rr_ExpensesOverAssets 2.08%
Fee Waiver or Reimbursement rr_FeeWaiverOrReimbursementOverAssets
Net Expenses (as a percentage of Assets) rr_NetExpensesOverAssets 2.08%
Expense Example, with Redemption, 1 Year rr_ExpenseExampleYear01 $ 311
Expense Example, with Redemption, 3 Years rr_ExpenseExampleYear03 652
Expense Example, with Redemption, 5 Years rr_ExpenseExampleYear05 1,119
Expense Example, with Redemption, 10 Years rr_ExpenseExampleYear10 2,410
Expense Example, No Redemption, 1 Year rr_ExpenseExampleNoRedemptionYear01 211
Expense Example, No Redemption, 3 Years rr_ExpenseExampleNoRedemptionYear03 652
Expense Example, No Redemption, 5 Years rr_ExpenseExampleNoRedemptionYear05 1,119
Expense Example, No Redemption, 10 Years rr_ExpenseExampleNoRedemptionYear10 $ 2,410
1 Year rr_AverageAnnualReturnYear01 12.56%
5 Years rr_AverageAnnualReturnYear05 10.73%
10 Years rr_AverageAnnualReturnYear10 11.98%
Retail | Thornburg Global Opportunities Fund | Thornburg Global Opportunities Fund - Class C | MSCI ACWI Net Total Return USD Index (reflects no deduction for fees, expenses, or U.S. taxes)  
Prospectus [Line Items] rr_ProspectusLineItems  
1 Year rr_AverageAnnualReturnYear01 18.54%
5 Years rr_AverageAnnualReturnYear05 14.40%
10 Years rr_AverageAnnualReturnYear10 11.85%
Retail | Thornburg Global Opportunities Fund | Thornburg Global Opportunities Fund - Class I  
Prospectus [Line Items] rr_ProspectusLineItems  
Trading Symbol dei_TradingSymbol THOIX
Maximum Sales Charge Imposed on Purchases (as a percentage of Offering Price) rr_MaximumSalesChargeImposedOnPurchasesOverOfferingPrice none
Maximum Deferred Sales Charge (as a percentage) rr_MaximumDeferredSalesChargeOverOther none
Management Fees (as a percentage of Assets) rr_ManagementFeesOverAssets 0.85%
Distribution and Service (12b-1) Fees rr_DistributionAndService12b1FeesOverAssets none
Other Expenses (as a percentage of Assets): rr_OtherExpensesOverAssets 0.21%
Expenses (as a percentage of Assets) rr_ExpensesOverAssets 1.06%
Fee Waiver or Reimbursement rr_FeeWaiverOrReimbursementOverAssets (0.07%) [3]
Net Expenses (as a percentage of Assets) rr_NetExpensesOverAssets 0.99%
Expense Example, with Redemption, 1 Year rr_ExpenseExampleYear01 $ 101
Expense Example, with Redemption, 3 Years rr_ExpenseExampleYear03 330
Expense Example, with Redemption, 5 Years rr_ExpenseExampleYear05 578
Expense Example, with Redemption, 10 Years rr_ExpenseExampleYear10 $ 1,288
1 Year rr_AverageAnnualReturnYear01 14.75%
5 Years rr_AverageAnnualReturnYear05 11.90%
10 Years rr_AverageAnnualReturnYear10 13.23%
Retail | Thornburg Global Opportunities Fund | Thornburg Global Opportunities Fund - Class I | MSCI ACWI Net Total Return USD Index (reflects no deduction for fees, expenses, or U.S. taxes)  
Prospectus [Line Items] rr_ProspectusLineItems  
1 Year rr_AverageAnnualReturnYear01 18.54%
5 Years rr_AverageAnnualReturnYear05 14.40%
10 Years rr_AverageAnnualReturnYear10 11.85%
Retail | Thornburg International Equity Fund  
Prospectus [Line Items] rr_ProspectusLineItems  
Risk/Return [Heading] rr_RiskReturnHeading International Equity Fund
Objective [Heading] rr_ObjectiveHeading Investment Goal
Objective, Primary [Text Block] rr_ObjectivePrimaryTextBlock

The Fund seeks long-term capital appreciation by investing in equity and debt securities of all types.
Objective, Secondary [Text Block] rr_ObjectiveSecondaryTextBlock

The secondary, non-fundamental goal of the Fund is to seek some current income.

Expense [Heading] rr_ExpenseHeading Fees and Expenses of the Fund
Expense Narrative [Text Block] rr_ExpenseNarrativeTextBlock

This table describes the fees and expenses that you may pay if you buy and hold shares of the Fund. You may qualify for discounts from the sales charges applicable to Class A shares if you or other qualifying account holders invest, or agree to invest in the future, at least $50,000 in the Thornburg Funds. More information about this and other discounts and sales charge waivers is available from your financial intermediary, in the Prospectus under the captions “Class A Sales Charge Waivers,” beginning on page 146, and “Appendix A – Sales Charge Waivers Offered by Financial Intermediaries,” beginning on page 200, and in the Statement of Additional Information under the caption “Additional Information Respecting Purchase and Redemption of Shares,” beginning on page 108.
Shareholder Fees Caption [Text] rr_ShareholderFeesCaption Shareholder Fees (fees paid directly from your investment)
Operating Expenses Caption [Text] rr_OperatingExpensesCaption Annual Fund Operating Expenses (expenses that you pay each year as a percentage of the value of your investment)
Fee Waiver or Reimbursement over Assets, Date of Termination rr_FeeWaiverOrReimbursementOverAssetsDateOfTermination February 1, 2023
Portfolio Turnover [Heading] rr_PortfolioTurnoverHeading Portfolio Turnover.
Portfolio Turnover [Text Block] rr_PortfolioTurnoverTextBlock

The Fund pays transaction costs, such as commissions, when it buys and sells securities (or “turns over”) its portfolio. A higher portfolio turnover rate may indicate higher transaction costs and may result in higher taxes when Fund shares are held in a taxable account. These costs, which are not reflected in Annual Fund Operating Expenses or in the Example, affect the Fund’s performance. During the most recent fiscal year, the Fund’s portfolio turnover rate was 42.85% of the average value of its portfolio.
Portfolio Turnover, Rate rr_PortfolioTurnoverRate 42.85%
Expense Breakpoint Discounts [Text] rr_ExpenseBreakpointDiscounts You may qualify for discounts from the sales charges applicable to Class A shares if you or other qualifying account holders invest, or agree to invest in the future, at least $50,000 in the Thornburg Funds.
Expense Breakpoint, Minimum Investment Required [Amount] rr_ExpenseBreakpointMinimumInvestmentRequiredAmount $ 50,000
Expense Example [Heading] rr_ExpenseExampleHeading Example.
Expense Example Narrative [Text Block] rr_ExpenseExampleNarrativeTextBlock

This Example is intended to help you compare the cost of investing in the Fund with the cost of investing in other mutual funds.

The Example assumes that you invest $10,000 in the Fund for the time periods indicated and then redeem all of your shares at the end of those periods. The Example also assumes that your investment has a 5% return each year, dividends and distributions are reinvested, and that the Fund’s operating expenses remain the same. Although your actual costs may be higher or lower, based on these assumptions your costs would be:
Expense Example, No Redemption Narrative [Text Block] rr_ExpenseExampleNoRedemptionNarrativeTextBlock

You would pay the following expenses if you did not redeem your Class C shares:
Strategy [Heading] rr_StrategyHeading Principal Investment Strategies
Strategy Narrative [Text Block] rr_StrategyNarrativeTextBlock

The Fund invests primarily in common stocks of non-U.S. companies and in depositary receipts associated with such stocks. The Fund may invest in developing countries, but under normal conditions those investments are expected to comprise a smaller proportion of the Fund than investments in developed countries. Under normal conditions, the Fund will invest at least 80% of its net assets in common stocks or depositary receipts.

The Fund’s investment advisor, Thornburg Investment Management, Inc. (“Thornburg”), intends to invest on an opportunistic basis where the Fund’s portfolio managers believe intrinsic value is not recognized by the marketplace. The Fund seeks to identify value in a broad or different context by investing in a diversified portfolio of stocks the Fund categorizes as basic values, consistent earners, and emerging franchises, when the portfolio managers believe these issues are value priced. The relative proportions of securities invested in each of those categories will vary over time. The Fund seeks to invest in promising companies, and may invest in stocks that reflect unfavorable market perceptions of the company or industry fundamentals. The Fund may invest in companies of any size, but invests primarily in the large and middle capitalization range of publicly traded companies.

Thornburg primarily uses individual issuer and industry analysis to make investment decisions. Value, for purposes of the Fund’s selection criteria, may consider both current and projected measures. Among the specific factors considered by Thornburg in identifying securities for inclusion in the Fund are:

•profitability

•price/earnings ratio

•price/book value ratio

•price/cash flow ratio

•debt/capital ratio

•dividend characteristics

•security and consistency of revenues

•EV (enterprise value)/EBITDA (earnings before interest, taxes, depreciation and amortization) ratio

•undervalued assets

•earnings growth potential

•industry growth characteristics

•industry leadership

•franchise value

•potential for favorable developments

•EBIT (earnings before interest and taxes)/interest expense ratio

The Fund categorizes its equity investments in the following three categories:

Basic Value: Companies generally operating in mature or cyclical industries and which generally exhibit more economic sensitivity and/or higher volatility in earnings and cash flow.

Consistent Earner: Companies which generally exhibit predictable growth, profitability, cash flow and/or dividends.

Emerging Franchise: Companies with the potential to grow at an above average rate because of a product or service that is establishing a new market and/or taking share from existing participants.

Inclusion of any investment in any of the three described categories represents the opinion of the advisor concerning the characteristics and prospects of the investment. There is no assurance that any company selected for investment will, once categorized in one of the three described investment categories, continue to have the positive characteristics or fulfill the expectations that the advisor had for the company when it was selected for investment, and any such company may not grow or may decline in earnings and size.

The Fund may sell an investment if Thornburg has identified a better investment opportunity, in response to changes in the conditions or business of the investment’s issuer or changes in overall market conditions, if Thornburg has a target price for the investment and that target price has been achieved, or if, in Thornburg’s opinion, the investment no longer serves to achieve the Fund’s investment goals.

The Fund’s policy of investing at least 80% of its net assets in common stocks or depositary receipts may be changed by the Fund’s Trustees without a shareholder vote upon 60 days’ notice to shareholders.
Risk [Heading] rr_RiskHeading Principal Investment Risks
Risk Narrative [Text Block] rr_RiskNarrativeTextBlock

An investment in the Fund is not a deposit in any bank and is not insured or guaranteed by the Federal Deposit Insurance Corporation or any other governmental agency. Accordingly, the loss of money is a risk of investing in the Fund. The value of the Fund’s shares varies from day to day and over time, and when you sell your shares they may be worth less than what you paid for them. The following is a summary of the principal risks of investing in the Fund.

Management Risk – The Fund is an actively managed portfolio, and the value of the Fund may be reduced if Thornburg pursues unsuccessful investments or fails to correctly identify risks affecting the broad economy or specific issuers in which the Fund invests.

Market and Economic Risk – The value of the Fund’s investments may decline and its share value may be reduced due to changes in general economic and market conditions. The value of a security may change in response to developments affecting entire economies, markets or industries, including changes in interest rates, political and legal developments, and general market volatility.

Equity Risk – The value of the Fund’s equity investments may fluctuate significantly over time in response to factors affecting individual issuers, particular industries, or the market as a whole. Additionally, common stock ranks below preferred stock and debt securities in claims for dividends and for assets of a company in a liquidation or bankruptcy.

Risks Affecting Specific Issuers – The value of a security may decline in response to developments affecting the specific issuer of the security, even if the overall industry or economy is unaffected. These developments may include a variety of factors, including but not limited to management issues or other corporate disruption, a decline in revenues or profitability, an increase in costs, or an adverse effect on the issuer’s competitive position.

Foreign Investment Risk – Investments in securities of foreign issuers may involve risks including adverse fluctuations in currency exchange rates, political instability, confiscations, taxes or restrictions on currency exchange, difficulty in selling foreign investments, and reduced legal protection.

Developing Country Risk – The risks which may affect investments in foreign issuers (see “Foreign Investment Risk,” above) may be more pronounced for investments in developing countries because the economies of those countries are usually less diversified, communications, transportation and economic infrastructures are less developed, and developing countries ordinarily have less established legal, political, business and social frameworks. At times the prices of equity securities of a developing country issuer may be extremely volatile. An issuer domiciled in a developed country may be similarly affected by these developing country risks to the extent that the issuer conducts its business in developing countries.

Foreign Currency Risk – Fluctuations in currency exchange rates can adversely affect the value of the Fund’s foreign investments. Such fluctuations may occur for a number of reasons, including market and economic conditions, or a government’s decision to devalue its currency or impose currency controls.

Risks Affecting Specific Countries or Regions – If a significant portion of the Fund’s assets is invested in issuers that are economically exposed to one country or region, the Fund’s share value may be more susceptible to the conditions and developments in that country or region, and potentially more volatile than the share value of a more geographically diversified fund. A specific country or region could also be adversely affected by conditions or developments arising in other countries. For example, the U.S. government could take actions to prohibit or restrict individuals or companies within the U.S. from purchasing or holding the shares of issuers in another country, which may limit the Fund’s ability to invest in that country or cause the Fund to have to sell investments in that country at less than desired prices. The nature and degree of the risks affecting a given country or region, and the extent of the Fund’s exposure to any such country or region, is expected to vary over time.

Risks Affecting Investments in China – A significant portion of the Fund’s assets may be invested in companies exposed to China. Risks affecting investments in China include a potential downturn in the Chinese economy, reduced liquidity or increased price volatility in the Chinese securities markets as a result of trading suspensions affecting Chinese issuers or other factors, the potential that the Chinese government may expand restrictions on foreign investments or the repatriation of capital, and the implementation of new tariffs or other trade barriers by China or its trading partners. A lack of transparency respecting Chinese companies may also reduce the Fund’s ability to conduct diligence respecting those companies’ accounting and governance standards, which may in turn reduce the Fund’s ability to detect fraudulent practices that may adversely affect the companies’ stock prices.

Small and Mid-Cap Company Risk – Investments in small-capitalization companies and mid-capitalization companies may involve additional risks, which may be relatively higher with smaller companies. These additional risks may result from limited product lines, more limited access to markets and financial resources, greater vulnerability to competition and changes in markets, lack of management depth, increased volatility in share price, and possible difficulties in valuing or selling these investments.

Credit Risk – The inability of an issuer to pay principal and interest on its debt obligations when due, or the downgrading of an issuer’s debt obligations by ratings agencies, may adversely affect the market’s perceptions of the issuer’s financial strength and may therefore result in declines in the issuer’s stock price.

Liquidity Risk – Due to a lack of demand in the marketplace or other factors, the Fund may not be able to sell some or all of its investments promptly, or may only be able to sell investments at less than desired prices.

Cybersecurity and Operational Risk – Operational failures, cyber-attacks or other disruptions that affect the Fund’s service providers, the Fund’s counterparties, other market participants or the issuers of securities held by the Fund may adversely affect the Fund and its shareholders, including by causing losses for the Fund or impairing Fund operations.

Additional information about Fund investments, investment strategies, and risks of investing in the Fund appears below beginning on page 118 of the Prospectus.
Risk Lose Money [Text] rr_RiskLoseMoney Accordingly, the loss of money is a risk of investing in the Fund.
RIsk Not Insured [Text] rr_RiskNotInsured An investment in the Fund is not a deposit in any bank and is not insured or guaranteed by the Federal Deposit Insurance Corporation or any other governmental agency.
Bar Chart and Performance Table [Heading] rr_BarChartAndPerformanceTableHeading Past Performance of the Fund
Performance Narrative [Text Block] rr_PerformanceNarrativeTextBlock

The following information provides some indication of the risks of investing in International Value Fund by showing how the Fund’s investment results vary from year to year. The bar chart shows how the annual total returns for Class A shares have been different in each full year shown. The average annual total return figures compare Class A, Class C and Class I share performance to the MSCI ACWI ex USA Net Total Return USD Index (primary index) and the MSCI EAFE Net Total Return USD Index (secondary index), each of which is a broad measure of market performance. Past performance (before and after taxes) is not necessarily an indication of how the Fund will perform in the future. The performance information shown is as of the calendar year ended December 31, 2021. Updated performance information may be obtained on the Thornburg website at Thornburg.com or by calling 1-800-847-0200.

Effective as of February 1, 2022, the MSCI ACWI ex USA Net Total Return USD Index replaced the MSCI EAFE Net Total Return USD Index as the Fund’s primary index. Thornburg believes that the MSCI ACWI ex USA Net Total Return USD Index more closely aligns with the Fund’s investment strategies than the MSCI EAFE Net Total Return USD Index.
Performance Information Illustrates Variability of Returns [Text] rr_PerformanceInformationIllustratesVariabilityOfReturns The following information provides some indication of the risks of investing in International Value Fund by showing how the Fund’s investment results vary from year to year.
Performance Availability Phone [Text] rr_PerformanceAvailabilityPhone 1-800-847-0200
Performance Availability Website Address [Text] rr_PerformanceAvailabilityWebSiteAddress Thornburg.com
Performance Past Does Not Indicate Future [Text] rr_PerformancePastDoesNotIndicateFuture Past performance (before and after taxes) is not necessarily an indication of how the Fund will perform in the future.
Bar Chart [Heading] rr_BarChartHeading Annual Total Returns – Class A Shares
Bar Chart Does Not Reflect Sales Loads [Text] rr_BarChartDoesNotReflectSalesLoads The sales charge for Class A shares is not reflected in the returns shown in the bar chart above, and the returns would be less if the charge was taken into account.
Bar Chart Closing [Text Block] rr_BarChartClosingTextBlock

Total
Returns

Quarter
ended

Highest Quarterly Results

18.46%

6/30/2020

Lowest Quarterly Results

(20.94)%

9/30/2011

The sales charge for Class A shares is not reflected in the returns shown in the bar chart above, and the returns would be less if the charge was taken into account.
Performance Table Heading rr_PerformanceTableHeading Average Annual Total Returns (periods ended 12-31-21)
Performance Table Market Index Changed rr_PerformanceTableMarketIndexChanged Effective as of February 1, 2022, the MSCI ACWI ex USA Net Total Return USD Index replaced the MSCI EAFE Net Total Return USD Index as the Fund’s primary index.
Performance Table Uses Highest Federal Rate rr_PerformanceTableUsesHighestFederalRate After-tax returns are calculated using the highest historical individual federal marginal income tax rates, and do not reflect state or local income taxes.
Performance Table Not Relevant to Tax Deferred rr_PerformanceTableNotRelevantToTaxDeferred Actual after-tax returns depend on an investor’s own tax situation and may differ from the returns shown, and after-tax returns shown are not relevant to investors who hold their Fund shares through tax-deferred arrangements, such as 401(k) plans or individual retirement accounts.
Performance Table One Class of after Tax Shown [Text] rr_PerformanceTableOneClassOfAfterTaxShown The after-tax returns shown relate only to Class A shares, and after-tax returns for other share classes will vary.
Performance Table Closing [Text Block] rr_PerformanceTableClosingTextBlock

After-tax returns are calculated using the highest historical individual federal marginal income tax rates, and do not reflect state or local income taxes. Actual after-tax returns depend on an investor’s own tax situation and may differ from the returns shown, and after-tax returns shown are not relevant to investors who hold their Fund shares through tax-deferred arrangements, such as 401(k) plans or individual retirement accounts. The after-tax returns shown relate only to Class A shares, and after-tax returns for other share classes will vary.
Retail | Thornburg International Equity Fund | Thornburg International Equity Fund - Class A  
Prospectus [Line Items] rr_ProspectusLineItems  
Trading Symbol dei_TradingSymbol TGVAX
Maximum Sales Charge Imposed on Purchases (as a percentage of Offering Price) rr_MaximumSalesChargeImposedOnPurchasesOverOfferingPrice 4.50%
Maximum Deferred Sales Charge (as a percentage) rr_MaximumDeferredSalesChargeOverOther none [4]
Management Fees (as a percentage of Assets) rr_ManagementFeesOverAssets 0.74%
Distribution and Service (12b-1) Fees rr_DistributionAndService12b1FeesOverAssets 0.25%
Other Expenses (as a percentage of Assets): rr_OtherExpensesOverAssets 0.26% [5]
Expenses (as a percentage of Assets) rr_ExpensesOverAssets 1.25%
Fee Waiver or Reimbursement rr_FeeWaiverOrReimbursementOverAssets
Net Expenses (as a percentage of Assets) rr_NetExpensesOverAssets 1.25%
Expense Example, with Redemption, 1 Year rr_ExpenseExampleYear01 $ 572
Expense Example, with Redemption, 3 Years rr_ExpenseExampleYear03 829
Expense Example, with Redemption, 5 Years rr_ExpenseExampleYear05 1,105
Expense Example, with Redemption, 10 Years rr_ExpenseExampleYear10 $ 1,893
Annual Return 2012 rr_AnnualReturn2012 15.33%
Annual Return 2013 rr_AnnualReturn2013 15.35%
Annual Return 2014 rr_AnnualReturn2014 (5.90%)
Annual Return 2015 rr_AnnualReturn2015 6.26%
Annual Return 2016 rr_AnnualReturn2016 (2.74%)
Annual Return 2017 rr_AnnualReturn2017 24.98%
Annual Return 2018 rr_AnnualReturn2018 (20.05%)
Annual Return 2019 rr_AnnualReturn2019 28.66%
Annual Return 2020 rr_AnnualReturn2020 22.36%
Annual Return 2021 rr_AnnualReturn2021 7.26%
Highest Quarterly Return, Label rr_HighestQuarterlyReturnLabel Highest Quarterly Results
Highest Quarterly Return, Date rr_BarChartHighestQuarterlyReturnDate Jun. 30, 2020
Highest Quarterly Return rr_BarChartHighestQuarterlyReturn 18.46%
Lowest Quarterly Return, Label rr_LowestQuarterlyReturnLabel Lowest Quarterly Results
Lowest Quarterly Return, Date rr_BarChartLowestQuarterlyReturnDate Sep. 30, 2011
Lowest Quarterly Return rr_BarChartLowestQuarterlyReturn (20.94%)
1 Year rr_AverageAnnualReturnYear01 2.44%
5 Years rr_AverageAnnualReturnYear05 10.01%
10 Years rr_AverageAnnualReturnYear10 7.62%
Retail | Thornburg International Equity Fund | Thornburg International Equity Fund - Class A | After Taxes on Distributions  
Prospectus [Line Items] rr_ProspectusLineItems  
1 Year rr_AverageAnnualReturnYear01 (1.50%)
5 Years rr_AverageAnnualReturnYear05 7.52%
10 Years rr_AverageAnnualReturnYear10 5.57%
Retail | Thornburg International Equity Fund | Thornburg International Equity Fund - Class A | After Taxes on Distributions and Sales  
Prospectus [Line Items] rr_ProspectusLineItems  
1 Year rr_AverageAnnualReturnYear01 2.73%
5 Years rr_AverageAnnualReturnYear05 7.19%
10 Years rr_AverageAnnualReturnYear10 5.49%
Retail | Thornburg International Equity Fund | Thornburg International Equity Fund - Class A | MSCI ACWI ex USA Net Total Return USD Index (reflects no deduction for fees, expenses, or U.S. taxes)  
Prospectus [Line Items] rr_ProspectusLineItems  
1 Year rr_AverageAnnualReturnYear01 7.82%
5 Years rr_AverageAnnualReturnYear05 9.61%
10 Years rr_AverageAnnualReturnYear10 7.28%
Retail | Thornburg International Equity Fund | Thornburg International Equity Fund - Class A | MSCI EAFE Net Total Return USD Index (reflects no deduction for fees, expenses, or U.S. taxes)  
Prospectus [Line Items] rr_ProspectusLineItems  
1 Year rr_AverageAnnualReturnYear01 11.26%
5 Years rr_AverageAnnualReturnYear05 9.55%
10 Years rr_AverageAnnualReturnYear10 8.03%
Retail | Thornburg International Equity Fund | Thornburg International Equity Fund - Class C  
Prospectus [Line Items] rr_ProspectusLineItems  
Trading Symbol dei_TradingSymbol THGCX
Maximum Sales Charge Imposed on Purchases (as a percentage of Offering Price) rr_MaximumSalesChargeImposedOnPurchasesOverOfferingPrice none
Maximum Deferred Sales Charge (as a percentage) rr_MaximumDeferredSalesChargeOverOther 1.00% [6]
Management Fees (as a percentage of Assets) rr_ManagementFeesOverAssets 0.74%
Distribution and Service (12b-1) Fees rr_DistributionAndService12b1FeesOverAssets 1.00%
Other Expenses (as a percentage of Assets): rr_OtherExpensesOverAssets 0.22% [5]
Expenses (as a percentage of Assets) rr_ExpensesOverAssets 1.96%
Fee Waiver or Reimbursement rr_FeeWaiverOrReimbursementOverAssets
Net Expenses (as a percentage of Assets) rr_NetExpensesOverAssets 1.96%
Expense Example, with Redemption, 1 Year rr_ExpenseExampleYear01 $ 299
Expense Example, with Redemption, 3 Years rr_ExpenseExampleYear03 615
Expense Example, with Redemption, 5 Years rr_ExpenseExampleYear05 1,057
Expense Example, with Redemption, 10 Years rr_ExpenseExampleYear10 2,285
Expense Example, No Redemption, 1 Year rr_ExpenseExampleNoRedemptionYear01 199
Expense Example, No Redemption, 3 Years rr_ExpenseExampleNoRedemptionYear03 615
Expense Example, No Redemption, 5 Years rr_ExpenseExampleNoRedemptionYear05 1,057
Expense Example, No Redemption, 10 Years rr_ExpenseExampleNoRedemptionYear10 $ 2,285
1 Year rr_AverageAnnualReturnYear01 5.58%
5 Years rr_AverageAnnualReturnYear05 10.23%
10 Years rr_AverageAnnualReturnYear10 7.34%
Retail | Thornburg International Equity Fund | Thornburg International Equity Fund - Class C | MSCI ACWI ex USA Net Total Return USD Index (reflects no deduction for fees, expenses, or U.S. taxes)  
Prospectus [Line Items] rr_ProspectusLineItems  
1 Year rr_AverageAnnualReturnYear01 7.82%
5 Years rr_AverageAnnualReturnYear05 9.61%
10 Years rr_AverageAnnualReturnYear10 7.28%
Retail | Thornburg International Equity Fund | Thornburg International Equity Fund - Class C | MSCI EAFE Net Total Return USD Index (reflects no deduction for fees, expenses, or U.S. taxes)  
Prospectus [Line Items] rr_ProspectusLineItems  
1 Year rr_AverageAnnualReturnYear01 11.26%
5 Years rr_AverageAnnualReturnYear05 9.55%
10 Years rr_AverageAnnualReturnYear10 8.03%
Retail | Thornburg International Equity Fund | Thornburg International Equity Fund - Class I  
Prospectus [Line Items] rr_ProspectusLineItems  
Trading Symbol dei_TradingSymbol TGVIX
Maximum Sales Charge Imposed on Purchases (as a percentage of Offering Price) rr_MaximumSalesChargeImposedOnPurchasesOverOfferingPrice none
Maximum Deferred Sales Charge (as a percentage) rr_MaximumDeferredSalesChargeOverOther none
Management Fees (as a percentage of Assets) rr_ManagementFeesOverAssets 0.74%
Distribution and Service (12b-1) Fees rr_DistributionAndService12b1FeesOverAssets none
Other Expenses (as a percentage of Assets): rr_OtherExpensesOverAssets 0.20% [5]
Expenses (as a percentage of Assets) rr_ExpensesOverAssets 0.94%
Fee Waiver or Reimbursement rr_FeeWaiverOrReimbursementOverAssets (0.04%) [7]
Net Expenses (as a percentage of Assets) rr_NetExpensesOverAssets 0.90%
Expense Example, with Redemption, 1 Year rr_ExpenseExampleYear01 $ 92
Expense Example, with Redemption, 3 Years rr_ExpenseExampleYear03 296
Expense Example, with Redemption, 5 Years rr_ExpenseExampleYear05 516
Expense Example, with Redemption, 10 Years rr_ExpenseExampleYear10 $ 1,151
1 Year rr_AverageAnnualReturnYear01 7.60%
5 Years rr_AverageAnnualReturnYear05 11.40%
10 Years rr_AverageAnnualReturnYear10 8.51%
Retail | Thornburg International Equity Fund | Thornburg International Equity Fund - Class I | MSCI ACWI ex USA Net Total Return USD Index (reflects no deduction for fees, expenses, or U.S. taxes)  
Prospectus [Line Items] rr_ProspectusLineItems  
1 Year rr_AverageAnnualReturnYear01 7.82%
5 Years rr_AverageAnnualReturnYear05 9.61%
10 Years rr_AverageAnnualReturnYear10 7.28%
Retail | Thornburg International Equity Fund | Thornburg International Equity Fund - Class I | MSCI EAFE Net Total Return USD Index (reflects no deduction for fees, expenses, or U.S. taxes)  
Prospectus [Line Items] rr_ProspectusLineItems  
1 Year rr_AverageAnnualReturnYear01 11.26%
5 Years rr_AverageAnnualReturnYear05 9.55%
10 Years rr_AverageAnnualReturnYear10 8.03%
Retail | Thornburg Better World International Fund  
Prospectus [Line Items] rr_ProspectusLineItems  
Risk/Return [Heading] rr_RiskReturnHeading Better World International Fund
Objective [Heading] rr_ObjectiveHeading Investment Goal
Objective, Primary [Text Block] rr_ObjectivePrimaryTextBlock

The Fund seeks long-term capital appreciation.

Expense [Heading] rr_ExpenseHeading Fees and Expenses of the Fund
Expense Narrative [Text Block] rr_ExpenseNarrativeTextBlock

This table describes the fees and expenses that you may pay if you buy and hold shares of the Fund. You may qualify for discounts from the sales charges applicable to Class A shares if you or other qualifying account holders invest, or agree to invest in the future, at least $50,000 in the Thornburg Funds. More information about this and other discounts and sales charge waivers is available from your financial intermediary, in the Prospectus under the captions “Class A Sales Charge Waivers,” beginning on page 146, and “Appendix A – Sales Charge Waivers Offered by Financial Intermediaries,” beginning on page 200, and in the Statement of Additional Information under the caption “Additional Information Respecting Purchase and Redemption of Shares,” beginning on page 108.
Shareholder Fees Caption [Text] rr_ShareholderFeesCaption Shareholder Fees (fees paid directly from your investment)
Operating Expenses Caption [Text] rr_OperatingExpensesCaption Annual Fund Operating Expenses (expenses that you pay each year as a percentage of the value of your investment)
Fee Waiver or Reimbursement over Assets, Date of Termination rr_FeeWaiverOrReimbursementOverAssetsDateOfTermination February 1, 2023
Portfolio Turnover [Heading] rr_PortfolioTurnoverHeading Portfolio Turnover.
Portfolio Turnover [Text Block] rr_PortfolioTurnoverTextBlock

The Fund pays transaction costs, such as commissions, when it buys and sells securities (or “turns over”) its portfolio. A higher portfolio turnover rate may indicate higher transaction costs and may result in higher taxes when Fund shares are held in a taxable account. These costs, which are not reflected in Annual Fund Operating Expenses or in the Example, affect the Fund’s performance. During the most recent fiscal year, the Fund’s portfolio turnover rate was 119.96% of the average value of its portfolio.
Portfolio Turnover, Rate rr_PortfolioTurnoverRate 119.96%
Expense Breakpoint Discounts [Text] rr_ExpenseBreakpointDiscounts You may qualify for discounts from the sales charges applicable to Class A shares if you or other qualifying account holders invest, or agree to invest in the future, at least $50,000 in the Thornburg Funds.
Expense Breakpoint, Minimum Investment Required [Amount] rr_ExpenseBreakpointMinimumInvestmentRequiredAmount $ 50,000
Expense Example [Heading] rr_ExpenseExampleHeading Example.
Expense Example Narrative [Text Block] rr_ExpenseExampleNarrativeTextBlock

This Example is intended to help you compare the cost of investing in the Fund with the cost of investing in other mutual funds.

The Example assumes that you invest $10,000 in the Fund for the time periods indicated and then redeem all of your shares at the end of those periods. The Example also assumes that your investment has a 5% return each year, dividends and distributions are reinvested, and that the Fund’s operating expenses remain the same. Although your actual costs may be higher or lower, based on these assumptions (and giving effect to fee waivers and expense reimbursements in the first year) your costs would be:
Expense Example, No Redemption Narrative [Text Block] rr_ExpenseExampleNoRedemptionNarrativeTextBlock

You would pay the following expenses if you did not redeem your Class C shares:
Strategy [Heading] rr_StrategyHeading Principal Investment Strategies
Strategy Narrative [Text Block] rr_StrategyNarrativeTextBlock

The Fund pursues its investment goal by investing primarily in a broad range of foreign equity securities or depositary receipts of foreign equity securities. When considering investments for the Fund, the Fund’s investment advisor, Thornburg Investment Management, Inc. (“Thornburg”), combines fundamental research on issuers with analysis of significant environmental, social and governance (“ESG”) characteristics, which Thornburg defines as those ESG factors that may materially affect an issuer’s risk and return profile and, accordingly, the issuer’s long-term investment performance.

The Fund may invest in any stock or other equity security which Thornburg believes may assist the Fund in pursuing its goal, including common stocks, preferred stocks and publicly traded real estate investment trusts. The Fund may invest in companies of any size, but invests primarily in the large and middle capitalization range of publicly traded companies. The Fund may also invest in developing country companies.

Thornburg intends to invest on an opportunistic basis where the Fund’s portfolio managers believe intrinsic value is not recognized by the marketplace. The Fund seeks to identify value in a broad or different context by investing in a diversified portfolio of stocks the Fund categorizes as basic values, consistent earners, and emerging franchises, when the portfolio managers believe these issues are value priced. The relative proportions of securities invested in each of those categories will vary over time.

The Fund categorizes its equity investments in the following three categories:

Basic Value: Companies generally operating in mature or cyclical industries and which generally exhibit more economic sensitivity and/or higher volatility in earnings and cash flow.

Consistent Earner: Companies which generally exhibit predictable growth, profitability, cash flow and/or dividends.

Emerging Franchise: Companies with the potential to grow at an above average rate because of a product or service that is establishing a new market and/or taking share from existing participants.

Inclusion of any investment in any of the three described categories represents the opinion of Thornburg concerning the characteristics and prospects of the investment. There is no assurance that any company selected for investment will, once categorized in one of the three described investment categories, continue to have the positive characteristics or fulfill the expectations that the advisor had for the company when it was selected for investment, and any such company may not grow or may decline in earnings and size.

The Fund’s investments are determined by individual issuer and industry analysis. Investment decisions also include consideration of domestic and international economic developments, outlooks for securities markets, interest rates and inflation, and the supply and demand for securities.

The Fund seeks to invest in companies which in Thornburg’s view are trading at discount to their intrinsic value and also demonstrate one or more significant positive ESG characteristics. Through Thornburg’s fundamental research process, Thornburg evaluates each potential investment based on a variety of factors, including traditional investment criteria such as the company’s ability to effectively allocate capital, willingness to pay dividends and repurchase shares, ability to sustain a competitive advantage, and ability to grow its core business. As part of its research process for the Fund’s investments, Thornburg also assesses each issuer’s ESG characteristics, focusing on those ESG characteristics which Thornburg believes are significant insofar as they are expected to materially affect the issuer’s investment performance. The specific ESG characteristics which Thornburg determines to be significant will vary over time and among different financial sectors and industries, but will generally include the following:

•Environmental characteristics, such as an issuer’s emissions and energy management practices;

•Social capital characteristics, such as an issuer’s data security and privacy practices;

•Human capital characteristics, such as an issuer’s labor practices;

•Business model and innovation characteristics, such as an issuer’s supply chain management practices; and

•Leadership and governance characteristics, such as an issuer’s practices toward managing legal and regulatory risks.

While Thornburg makes its own judgments about the ESG characteristics of each investment, Thornburg’s approach may be informed by third party data and other research tools, including consideration of the list of material ESG factors established by the Sustainability Accounting Standards Board.

Market observers differ in their perspectives and understanding of the importance of ESG factors to investment decisions. In its evaluation of potential investments, Thornburg may identify as significant certain ESG characteristics that are different from the characteristics that other investors may consider significant. Thornburg consequently may not consider the same ESG characteristics that other investors might consider in evaluating a potential investment. Similarly, Thornburg may assess the significance of ESG characteristics differently than some other investors, assigning either greater or lesser emphasis to a characteristic than another investor might assign.

The Fund may sell an investment if Thornburg has identified a better investment opportunity, in response to changes in the conditions or business of the investment’s issuer or changes in overall market conditions, if Thornburg has a target price for the investment and that target price has been achieved, or if, in Thornburg’s opinion, the investment no longer serves to achieve the Fund’s investment goals.
Risk [Heading] rr_RiskHeading Principal Investment Risks
Risk Narrative [Text Block] rr_RiskNarrativeTextBlock

An investment in the Fund is not a deposit in any bank and is not insured or guaranteed by the Federal Deposit Insurance Corporation or any other governmental agency. Accordingly, the loss of money is a risk of investing in the Fund. The value of the Fund’s shares varies from day to day and over time, and when you sell your shares they may be worth less than what you paid for them. The following is a summary of the principal risks of investing in the Fund.

Management Risk – The Fund is an actively managed portfolio, and the value of the Fund may be reduced if Thornburg pursues unsuccessful investments or fails to correctly identify risks affecting the broad economy or specific issuers in which the Fund invests.

Market and Economic Risk – The value of the Fund’s investments may decline and its share value may be reduced due to changes in general economic and market conditions. The value of a security may change in response to developments affecting entire economies, markets or industries, including changes in interest rates, political and legal developments, and general market volatility.

Equity Risk – The value of the Fund’s equity investments may fluctuate significantly over time in response to factors affecting individual issuers, particular industries, or the market as a whole. Additionally, common stock ranks below preferred stock and debt securities in claims for dividends and for assets of a company in a liquidation or bankruptcy.

Risks Affecting Specific Issuers – The value of a security may decline in response to developments affecting the specific issuer of the security, even if the overall industry or economy is unaffected. These developments may include a variety of factors, including but not limited to management issues or other corporate disruption, a decline in revenues or profitability, an increase in costs, or an adverse effect on the issuer’s competitive position.

Foreign Investment Risk – Investments in securities of foreign issuers may involve risks including adverse fluctuations in currency exchange rates, political instability, confiscations, taxes or restrictions on currency exchange, difficulty in selling foreign investments, and reduced legal protection.

Developing Country Risk – The risks which may affect investments in foreign issuers (see “Foreign Investment Risk,” above) may be more pronounced for investments in developing countries because the economies of those countries are usually less diversified, communications, transportation and economic infrastructures are less developed, and developing countries ordinarily have less established legal, political, business and social frameworks. At times the prices of equity securities of a developing country issuer may be extremely volatile. An issuer domiciled in a developed country may be similarly affected by these developing country risks to the extent that the issuer conducts its business in developing countries.

Foreign Currency Risk – Fluctuations in currency exchange rates can adversely affect the value of the Fund’s foreign investments. Such fluctuations may occur for a number of reasons, including market and economic conditions, or a government’s decision to devalue its currency or impose currency controls.

Risks Affecting Specific Countries or Regions – If a significant portion of the Fund’s assets is invested in issuers that are economically exposed to one country or region, the Fund’s share value may be more susceptible to the conditions and developments in that country or region, and potentially more volatile than the share value of a more geographically diversified fund. A specific country or region could also be adversely affected by conditions or developments arising in other countries. For example, the U.S. government could take actions to prohibit or restrict individuals or companies within the U.S. from purchasing or holding the shares of issuers in another country, which may limit the Fund’s ability to invest in that country or cause the Fund to have to sell investments in that country at less than desired prices. The nature and degree of the risks affecting a given country or region, and the extent of the Fund’s exposure to any such country or region, is expected to vary over time.

Risks Affecting Investments in China – A significant portion of the Fund’s assets may be invested in companies exposed to China. Risks affecting investments in China include a potential downturn in the Chinese economy, reduced liquidity or increased price volatility in the Chinese securities markets as a result of trading suspensions affecting Chinese issuers or other factors, the potential that the Chinese government may expand restrictions on foreign investments or the repatriation of capital, and the implementation of new tariffs or other trade barriers by China or its trading partners. A lack of transparency respecting Chinese companies may also reduce the Fund’s ability to conduct diligence respecting those companies’ accounting and governance standards, which may in turn reduce the Fund’s ability to detect fraudulent practices that may adversely affect the companies’ stock prices.

Small and Mid-Cap Company Risk – Investments in small capitalization companies and mid-capitalization companies may involve additional risks, which may be relatively higher with smaller companies. These additional risks may result from limited product lines, more limited access to markets and financial resources, greater vulnerability to competition and changes in markets, lack of management depth, increased volatility in share price, and possible difficulties in valuing or selling these investments.

Credit Risk – The inability of an issuer to pay principal and interest on its debt obligations when due, or the downgrading of an issuer’s debt obligations by ratings agencies, may adversely affect the market’s perceptions of the issuer’s financial strength and may therefore result in declines in the issuer’s stock price.

Liquidity Risk – Due to a lack of demand in the marketplace or other factors, the Fund may not be able to sell some or all of its investments promptly, or may only be able to sell investments at less than desired prices. This risk may be more pronounced for the Fund’s investments in developing countries.

ESG Investing Risk – Thornburg’s assessments of company ESG characteristics may result in decisions not to purchase, or to sell, investments which are otherwise consistent with the Fund’s investment goal and subsequently produce attractive investment performance, and Thornburg’s assessments of these characteristics may at times reduce the Fund’s exposure to market sectors or types of investments that produce positive investment performance. The application of ESG principles and the perceptions of the commitment of a given company to ESG principles vary among investors, analysts and other market observers. Consequently, Thornburg’s assessments respecting the ESG characteristics associated with any company may differ from the perceptions of other persons, including other mutual funds. Additionally, it may be difficult in certain instances for Thornburg to evaluate correctly a company’s commitment to positive ESG practices, and a failure to do so may result in investment in companies with practices that are not consistent with the Fund’s aspirations.

Real Estate Risk – The Fund’s investments in publicly traded real estate investment trusts (“REITs”) are subject to risks affecting real estate investments generally (including market conditions, competition, property obsolescence, changes in interest rates and casualty to real estate), as well as risks specifically affecting REITs (the quality and skill of REIT management and the internal expenses of the REIT).

Cybersecurity and Operational Risk – Operational failures, cyber-attacks or other disruptions that affect the Fund’s service providers, the Fund’s counterparties, other market participants or the issuers of securities held by the Fund may adversely affect the Fund and its shareholders, including by causing losses for the Fund or impairing Fund operations.

Additional information about Fund investments, investment strategies and risks of investing in the Fund appears beginning on page 118 of the Prospectus.
Risk Lose Money [Text] rr_RiskLoseMoney Accordingly, the loss of money is a risk of investing in the Fund.
RIsk Not Insured [Text] rr_RiskNotInsured An investment in the Fund is not a deposit in any bank and is not insured or guaranteed by the Federal Deposit Insurance Corporation or any other governmental agency.
Bar Chart and Performance Table [Heading] rr_BarChartAndPerformanceTableHeading Past Performance of the Fund
Performance Narrative [Text Block] rr_PerformanceNarrativeTextBlock

The following information provides some indication of the risks of investing in Better World International Fund by showing how the Fund’s investment results vary from year to year. The bar chart shows how the annual total returns for Class A shares of the Fund have been different in each full year shown. The average annual total return figures compare Class A, Class C and Class I share performance to the MSCI ACWI ex USA Net Total Return USD Index, net of withholding taxes on dividends, which is a broad measure of market performance. Past performance (before and after taxes) is not necessarily an indication of how the Fund will perform in the future. The performance information shown is as of the calendar year ended December 31, 2021. Updated performance information may be obtained on the Thornburg website at Thornburg.com or by calling 1-800-847-0200.
Performance Information Illustrates Variability of Returns [Text] rr_PerformanceInformationIllustratesVariabilityOfReturns The following information provides some indication of the risks of investing in Better World International Fund by showing how the Fund’s investment results vary from year to year.
Performance Availability Phone [Text] rr_PerformanceAvailabilityPhone 1-800-847-0200
Performance Availability Website Address [Text] rr_PerformanceAvailabilityWebSiteAddress Thornburg.com
Performance Past Does Not Indicate Future [Text] rr_PerformancePastDoesNotIndicateFuture Past performance (before and after taxes) is not necessarily an indication of how the Fund will perform in the future.
Bar Chart [Heading] rr_BarChartHeading Annual Total Returns – Class A Shares
Bar Chart Does Not Reflect Sales Loads [Text] rr_BarChartDoesNotReflectSalesLoads The sales charge for Class A shares is not reflected in the returns shown on the bar chart, and the returns would be less if the charge was taken into account.
Bar Chart Closing [Text Block] rr_BarChartClosingTextBlock

Total
Returns

Quarter
ended

Highest Quarterly Results

22.85%

6/30/2020

Lowest Quarterly Results

(19.58)%

3/31/2020

The sales charge for Class A shares is not reflected in the returns shown on the bar chart, and the returns would be less if the charge was taken into account.
Performance Table Heading rr_PerformanceTableHeading Average Annual Total Returns (periods ended 12-31-21)
Performance Table Uses Highest Federal Rate rr_PerformanceTableUsesHighestFederalRate After-tax returns are calculated using the historical highest individual federal marginal income tax rates, and do not reflect state or local income taxes.
Performance Table Not Relevant to Tax Deferred rr_PerformanceTableNotRelevantToTaxDeferred Actual after-tax returns depend on an investor’s own tax situation and may differ from the returns shown, and after-tax returns shown are not relevant to investors who hold their Fund shares through tax-deferred arrangements, such as 401(k) plans or individual retirement accounts.
Performance Table One Class of after Tax Shown [Text] rr_PerformanceTableOneClassOfAfterTaxShown The after-tax returns shown relate only to Class A shares, and after-tax returns for other share classes will vary.
Performance Table Closing [Text Block] rr_PerformanceTableClosingTextBlock

After-tax returns are calculated using the historical highest individual federal marginal income tax rates, and do not reflect state or local income taxes. Actual after-tax returns depend on an investor’s own tax situation and may differ from the returns shown, and after-tax returns shown are not relevant to investors who hold their Fund shares through tax-deferred arrangements, such as 401(k) plans or individual retirement accounts. The after-tax returns shown relate only to Class A shares, and after-tax returns for other share classes will vary.

The performance information shown above may include gains attributable to the Fund’s investments in shares of companies through initial public offerings (“IPOs”). There can be no assurance that the Fund will have continued access to profitable IPOs and, as the Fund’s assets grow, the impact of the Fund’s investment in IPOs on the performance of the Fund may decline.
Retail | Thornburg Better World International Fund | Thornburg Better World International Fund - Class A  
Prospectus [Line Items] rr_ProspectusLineItems  
Trading Symbol dei_TradingSymbol TBWAX
Maximum Sales Charge Imposed on Purchases (as a percentage of Offering Price) rr_MaximumSalesChargeImposedOnPurchasesOverOfferingPrice 4.50%
Maximum Deferred Sales Charge (as a percentage) rr_MaximumDeferredSalesChargeOverOther none [8]
Management Fees (as a percentage of Assets) rr_ManagementFeesOverAssets 0.98%
Distribution and Service (12b-1) Fees rr_DistributionAndService12b1FeesOverAssets 0.25%
Other Expenses (as a percentage of Assets): rr_OtherExpensesOverAssets 0.34%
Expenses (as a percentage of Assets) rr_ExpensesOverAssets 1.57%
Fee Waiver or Reimbursement rr_FeeWaiverOrReimbursementOverAssets [9]
Net Expenses (as a percentage of Assets) rr_NetExpensesOverAssets 1.57%
Expense Example, with Redemption, 1 Year rr_ExpenseExampleYear01 $ 603
Expense Example, with Redemption, 3 Years rr_ExpenseExampleYear03 923
Expense Example, with Redemption, 5 Years rr_ExpenseExampleYear05 1,267
Expense Example, with Redemption, 10 Years rr_ExpenseExampleYear10 $ 2,233
Annual Return 2016 rr_AnnualReturn2016 6.76%
Annual Return 2017 rr_AnnualReturn2017 21.88%
Annual Return 2018 rr_AnnualReturn2018 (14.28%)
Annual Return 2019 rr_AnnualReturn2019 23.72%
Annual Return 2020 rr_AnnualReturn2020 25.85%
Annual Return 2021 rr_AnnualReturn2021 20.39%
Highest Quarterly Return, Label rr_HighestQuarterlyReturnLabel Highest Quarterly Results
Highest Quarterly Return, Date rr_BarChartHighestQuarterlyReturnDate Jun. 30, 2020
Highest Quarterly Return rr_BarChartHighestQuarterlyReturn 22.85%
Lowest Quarterly Return, Label rr_LowestQuarterlyReturnLabel Lowest Quarterly Results
Lowest Quarterly Return, Date rr_BarChartLowestQuarterlyReturnDate Mar. 31, 2020
Lowest Quarterly Return rr_BarChartLowestQuarterlyReturn (19.58%)
1 Year rr_AverageAnnualReturnYear01 14.98%
5 Years rr_AverageAnnualReturnYear05 13.34%
Since Inception rr_AverageAnnualReturnSinceInception 12.42%
Inception Date rr_AverageAnnualReturnInceptionDate Oct. 01, 2015
Retail | Thornburg Better World International Fund | Thornburg Better World International Fund - Class A | After Taxes on Distributions  
Prospectus [Line Items] rr_ProspectusLineItems  
1 Year rr_AverageAnnualReturnYear01 9.89%
5 Years rr_AverageAnnualReturnYear05 11.30%
Since Inception rr_AverageAnnualReturnSinceInception 10.35%
Retail | Thornburg Better World International Fund | Thornburg Better World International Fund - Class A | After Taxes on Distributions and Sales  
Prospectus [Line Items] rr_ProspectusLineItems  
1 Year rr_AverageAnnualReturnYear01 9.95%
5 Years rr_AverageAnnualReturnYear05 9.81%
Since Inception rr_AverageAnnualReturnSinceInception 9.05%
Retail | Thornburg Better World International Fund | Thornburg Better World International Fund - Class A | MSCI ACWI ex USA Net Total Return USD Index (reflects no deduction for fees, expenses, or U.S. taxes)  
Prospectus [Line Items] rr_ProspectusLineItems  
1 Year rr_AverageAnnualReturnYear01 7.82%
5 Years rr_AverageAnnualReturnYear05 9.61%
Since Inception rr_AverageAnnualReturnSinceInception 8.93%
Retail | Thornburg Better World International Fund | Thornburg Better World International Fund - Class C  
Prospectus [Line Items] rr_ProspectusLineItems  
Trading Symbol dei_TradingSymbol TBWCX
Maximum Sales Charge Imposed on Purchases (as a percentage of Offering Price) rr_MaximumSalesChargeImposedOnPurchasesOverOfferingPrice none
Maximum Deferred Sales Charge (as a percentage) rr_MaximumDeferredSalesChargeOverOther 1.00% [10]
Management Fees (as a percentage of Assets) rr_ManagementFeesOverAssets 0.98%
Distribution and Service (12b-1) Fees rr_DistributionAndService12b1FeesOverAssets 1.00%
Other Expenses (as a percentage of Assets): rr_OtherExpensesOverAssets 0.87%
Expenses (as a percentage of Assets) rr_ExpensesOverAssets 2.85%
Fee Waiver or Reimbursement rr_FeeWaiverOrReimbursementOverAssets (0.66%) [9]
Net Expenses (as a percentage of Assets) rr_NetExpensesOverAssets 2.19%
Expense Example, with Redemption, 1 Year rr_ExpenseExampleYear01 $ 322
Expense Example, with Redemption, 3 Years rr_ExpenseExampleYear03 821
Expense Example, with Redemption, 5 Years rr_ExpenseExampleYear05 1,445
Expense Example, with Redemption, 10 Years rr_ExpenseExampleYear10 3,129
Expense Example, No Redemption, 1 Year rr_ExpenseExampleNoRedemptionYear01 222
Expense Example, No Redemption, 3 Years rr_ExpenseExampleNoRedemptionYear03 821
Expense Example, No Redemption, 5 Years rr_ExpenseExampleNoRedemptionYear05 1,445
Expense Example, No Redemption, 10 Years rr_ExpenseExampleNoRedemptionYear10 $ 3,129
1 Year rr_AverageAnnualReturnYear01 18.36%
5 Years rr_AverageAnnualReturnYear05 13.70%
Since Inception rr_AverageAnnualReturnSinceInception 12.56%
Inception Date rr_AverageAnnualReturnInceptionDate Oct. 01, 2015
Retail | Thornburg Better World International Fund | Thornburg Better World International Fund - Class C | MSCI ACWI ex USA Net Total Return USD Index (reflects no deduction for fees, expenses, or U.S. taxes)  
Prospectus [Line Items] rr_ProspectusLineItems  
1 Year rr_AverageAnnualReturnYear01 7.82%
5 Years rr_AverageAnnualReturnYear05 9.61%
Since Inception rr_AverageAnnualReturnSinceInception 8.93%
Retail | Thornburg Better World International Fund | Thornburg Better World International Fund - Class I  
Prospectus [Line Items] rr_ProspectusLineItems  
Trading Symbol dei_TradingSymbol TBWIX
Maximum Sales Charge Imposed on Purchases (as a percentage of Offering Price) rr_MaximumSalesChargeImposedOnPurchasesOverOfferingPrice none
Maximum Deferred Sales Charge (as a percentage) rr_MaximumDeferredSalesChargeOverOther none
Management Fees (as a percentage of Assets) rr_ManagementFeesOverAssets 0.98%
Distribution and Service (12b-1) Fees rr_DistributionAndService12b1FeesOverAssets none
Other Expenses (as a percentage of Assets): rr_OtherExpensesOverAssets 0.23%
Expenses (as a percentage of Assets) rr_ExpensesOverAssets 1.21%
Fee Waiver or Reimbursement rr_FeeWaiverOrReimbursementOverAssets (0.31%) [9]
Net Expenses (as a percentage of Assets) rr_NetExpensesOverAssets 0.90%
Expense Example, with Redemption, 1 Year rr_ExpenseExampleYear01 $ 92
Expense Example, with Redemption, 3 Years rr_ExpenseExampleYear03 353
Expense Example, with Redemption, 5 Years rr_ExpenseExampleYear05 635
Expense Example, with Redemption, 10 Years rr_ExpenseExampleYear10 $ 1,438
1 Year rr_AverageAnnualReturnYear01 20.92%
5 Years rr_AverageAnnualReturnYear05 15.19%
Since Inception rr_AverageAnnualReturnSinceInception 14.04%
Inception Date rr_AverageAnnualReturnInceptionDate Oct. 01, 2015
Retail | Thornburg Better World International Fund | Thornburg Better World International Fund - Class I | MSCI ACWI ex USA Net Total Return USD Index (reflects no deduction for fees, expenses, or U.S. taxes)  
Prospectus [Line Items] rr_ProspectusLineItems  
1 Year rr_AverageAnnualReturnYear01 7.82%
5 Years rr_AverageAnnualReturnYear05 9.61%
Since Inception rr_AverageAnnualReturnSinceInception 8.93%
Retail | Thornburg International Growth Fund  
Prospectus [Line Items] rr_ProspectusLineItems  
Risk/Return [Heading] rr_RiskReturnHeading International Growth Fund
Objective [Heading] rr_ObjectiveHeading Investment Goal
Objective, Primary [Text Block] rr_ObjectivePrimaryTextBlock

The Fund seeks long-term growth of capital by investing in equity securities selected for their growth potential.

Expense [Heading] rr_ExpenseHeading Fees and Expenses of the Fund
Expense Narrative [Text Block] rr_ExpenseNarrativeTextBlock

This table describes the fees and expenses that you may pay if you buy and hold shares of the Fund. You may qualify for discounts from the sales charges applicable to Class A shares if you or other qualifying account holders invest, or agree to invest in the future, at least $50,000 in the Thornburg Funds. More information about this and other discounts and sales charge waivers is available from your financial intermediary, in the Prospectus under the captions “Class A Sales Charge Waivers,” beginning on page 146, and “Appendix A – Sales Charge Waivers Offered by Financial Intermediaries,” beginning on page 200, and in the Statement of Additional Information under the caption “Additional Information Respecting Purchase and Redemption of Shares,” beginning on page 108.
Shareholder Fees Caption [Text] rr_ShareholderFeesCaption Shareholder Fees (fees paid directly from your investment)
Operating Expenses Caption [Text] rr_OperatingExpensesCaption Annual Fund Operating Expenses (expenses that you pay each year as a percentage of the value of your investment)
Portfolio Turnover [Heading] rr_PortfolioTurnoverHeading Portfolio Turnover.
Portfolio Turnover [Text Block] rr_PortfolioTurnoverTextBlock

The Fund pays transaction costs, such as commissions, when it buys and sells securities (or “turns over”) its portfolio. A higher portfolio turnover rate may indicate higher transaction costs and may result in higher taxes when Fund shares are held in a taxable account. These costs, which are not reflected in Annual Fund Operating Expenses or in the Example, affect the Fund’s performance. During the most recent fiscal year, the Fund’s portfolio turnover rate was 34.41% of the average value of its portfolio.
Portfolio Turnover, Rate rr_PortfolioTurnoverRate 34.41%
Expense Breakpoint Discounts [Text] rr_ExpenseBreakpointDiscounts You may qualify for discounts from the sales charges applicable to Class A shares if you or other qualifying account holders invest, or agree to invest in the future, at least $50,000 in the Thornburg Funds.
Expense Breakpoint, Minimum Investment Required [Amount] rr_ExpenseBreakpointMinimumInvestmentRequiredAmount $ 50,000
Expense Example [Heading] rr_ExpenseExampleHeading Example.
Expense Example Narrative [Text Block] rr_ExpenseExampleNarrativeTextBlock

This Example is intended to help you compare the cost of investing in the Fund with the cost of investing in other mutual funds.

The Example assumes that you invest $10,000 in the Fund for the time periods indicated and then redeem all of your shares at the end of those periods. The Example also assumes that your investment has a 5% return each year, dividends and distributions are reinvested, and that the Fund’s operating expenses remain the same. Although your actual costs may be higher or lower, based on these assumptions (and giving effect to fee waivers and expense reimbursements in the first year), your costs would be:
Expense Example, No Redemption Narrative [Text Block] rr_ExpenseExampleNoRedemptionNarrativeTextBlock

You would pay the following expenses if you did not redeem your Class C shares:
Strategy [Heading] rr_StrategyHeading Principal Investment Strategies
Strategy Narrative [Text Block] rr_StrategyNarrativeTextBlock

The Fund expects to invest primarily in equity securities from issuers around the world (primarily common stocks) selected for their growth potential and, under normal market conditions, invests at least 75% of its assets in foreign securities or depositary receipts of foreign securities. However, the Fund may own a variety of securities, including domestic equity securities. The Fund may invest in developing countries.

The Fund’s investment advisor, Thornburg Investment Management, Inc. (“Thornburg”) intends to invest in companies that it believes will have growing revenues and earnings. The Fund can invest in companies of any size, from larger, well-established companies to smaller, emerging growth companies.

Thornburg primarily uses individual issuer and industry analysis to make investment decisions. Among the specific factors considered by Thornburg in identifying securities for inclusion in the Fund are:

•earnings growth potential

•business model

•industry growth potential

•industry leadership

•asset appreciation potential

•potential size of business

•price/earnings ratio

•price/revenue ratio

•PE/growth rate ratio

•price/cash flow ratio

•enterprise value/EBITDA (earnings before interest, taxes, depreciation and amortization) ratio

•management strength

•debt/capital ratio

The Fund typically makes equity investments in the following three types of companies:

Growth Industry Leaders: Companies in this category often have leadership positions in growing markets. In some cases these companies may have dominant market share. These companies tend to be larger and more established.

Consistent Growers: Companies in this category generally exhibit steady earnings or revenue growth, or both. These companies may have subscription or other recurring revenue profiles. Given their business models, these companies may outperform in weak markets.

Emerging Growth Companies: Companies often addressing a new market or carving out a niche in an existing market. Companies in this category may experience rapid growth, and tend to be smaller, earlier stage companies. These companies may exhibit high volatility.

Inclusion of any investment in any of the three described categories represents the opinion of the advisor concerning the characteristics and prospects of the investment. There is no assurance that any company selected for investment will, once categorized in one of the three described investment categories, continue to have the positive characteristics or fulfill the expectations that the advisor had for the company when it was selected for investment, and any such company may not grow or may decline in earnings and size.

In conjunction with individual issuer analysis, Thornburg may identify and invest at times with a greater emphasis in industries or economic sectors it expects to experience growth. This approach may at times produce a greater emphasis on investment in certain industries or economic sectors, such as technology, financial services, healthcare or biotechnology. The Fund does not have a strategy to invest in particular industry or economic sectors, and its exposures to particular industries or economic sectors are expected to vary over time. Investment decisions are also based on domestic and international economic developments, outlooks for securities markets, interest rates and inflation, and the supply and demand for securities.

The Fund may sell an investment if Thornburg has identified a better investment opportunity, in response to changes in the conditions or business of the investment’s issuer or changes in overall market conditions, if Thornburg has a target price for the investment and that target price has been achieved, or if, in Thornburg’s opinion, the investment no longer serves to achieve the Fund’s investment goals.
Risk [Heading] rr_RiskHeading Principal Investment Risks
Risk Narrative [Text Block] rr_RiskNarrativeTextBlock

An investment in the Fund is not a deposit in any bank and is not insured or guaranteed by the Federal Deposit Insurance Corporation or any other governmental agency. Accordingly, the loss of money is a risk of investing in the Fund. The value of the Fund’s shares varies from day to day and over time, and when you sell your shares they may be worth less than what you paid for them. The following is a summary of the principal risks of investing in the Fund.

Management Risk – The Fund is an actively managed portfolio, and the value of the Fund may be reduced if Thornburg pursues unsuccessful investments or fails to correctly identify risks affecting the broad economy or specific issuers in which the Fund invests.

Market and Economic Risk – The value of the Fund’s investments may decline and its share value may be reduced due to changes in general economic and market conditions. The value of a security may change in response to developments affecting entire economies, markets or industries, including changes in interest rates, political and legal developments, and general market volatility.

Equity Risk – The value of the Fund’s equity investments may fluctuate significantly over time in response to factors affecting individual issuers, particular industries, or the market as a whole. Additionally, common stock ranks below preferred stock and debt securities in claims for dividends and for assets of a company in a liquidation or bankruptcy.

Risks Affecting Specific Issuers – The value of a security may decline in response to developments affecting the specific issuer of the security, even if the overall industry or economy is unaffected. These developments may include a variety of factors, including but not limited to management issues or other corporate disruption, a decline in revenues or profitability, an increase in costs, or an adverse effect on the issuer’s competitive position.

Foreign Investment Risk – Investments in securities of foreign issuers may involve risks including adverse fluctuations in currency exchange rates, political instability, confiscations, taxes or restrictions on currency exchange, difficulty in selling foreign investments, and reduced legal protection.

Developing Country Risk – The risks which may affect investments in foreign issuers (see “Foreign Investment Risk,” above) may be more pronounced for investments in developing countries because the economies of those countries are usually less diversified, communications, transportation and economic infrastructures are less developed, and developing countries ordinarily have less established legal, political, business and social frameworks. At times the prices of equity securities of a developing country issuer may be extremely volatile. An issuer domiciled in a developed country may be similarly affected by these developing country risks to the extent that the issuer conducts its business in developing countries.

Foreign Currency Risk – Fluctuations in currency exchange rates can adversely affect the value of the Fund’s foreign investments. Such fluctuations may occur for a number of reasons, including market and economic conditions, or a government’s decision to devalue its currency or impose currency controls.

Risks Affecting Specific Countries or Regions – If a significant portion of the Fund’s assets is invested in issuers that are economically exposed to one country or region, the Fund’s share value may be more susceptible to the conditions and developments in that country or region, and potentially more volatile than the share value of a more geographically diversified fund. A specific country or region could also be adversely affected by conditions or developments arising in other countries. For example, the U.S. government could take actions to prohibit or restrict individuals or companies within the U.S. from purchasing or holding the shares of issuers in another country, which may limit the Fund’s ability to invest in that country or cause the Fund to have to sell investments in that country at less than desired prices. The nature and degree of the risks affecting a given country or region, and the extent of the Fund’s exposure to any such country or region, is expected to vary over time.

Small and Mid-Cap Company Risk – Investments in small-capitalization companies and mid-capitalization companies, including smaller, earlier stage companies, may involve additional risks. These risks may be relatively higher with smaller companies. These additional risks may result from limited product lines, more limited access to markets and financial resources, greater vulnerability to competition and changes in markets, lack of management depth, increased volatility in share price, and possible difficulties in valuing or selling these investments.

Credit Risk – The inability of an issuer to pay principal and interest on its debt obligations when due, or the downgrading of an issuer’s debt obligations by ratings agencies, may adversely affect the market’s perceptions of the issuer’s financial strength and may therefore result in declines in the issuer’s stock price.

Liquidity Risk – Due to a lack of demand in the marketplace or other factors, the Fund may not be able to sell some or all of its investments promptly, or may only be able to sell investments at less than desired prices. This risk may be more pronounced for the Fund’s investments in developing countries.

Cybersecurity and Operational Risk – Operational failures, cyber-attacks or other disruptions that affect the Fund’s service providers, the Fund’s counterparties, other market participants or the issuers of securities held by the Fund may adversely affect the Fund and its shareholders, including by causing losses for the Fund or impairing Fund operations.

Additional information about Fund investments, investment strategies, and risks of investing in the Fund appears below beginning on page 118 of the Prospectus.
Risk Lose Money [Text] rr_RiskLoseMoney Accordingly, the loss of money is a risk of investing in the Fund.
RIsk Not Insured [Text] rr_RiskNotInsured An investment in the Fund is not a deposit in any bank and is not insured or guaranteed by the Federal Deposit Insurance Corporation or any other governmental agency.
Bar Chart and Performance Table [Heading] rr_BarChartAndPerformanceTableHeading Past Performance of the Fund
Performance Narrative [Text Block] rr_PerformanceNarrativeTextBlock

The following information provides some indication of the risks of investing in International Growth Fund by showing how the Fund’s investment results vary from year to year. The bar chart shows how the annual total return for Class A shares has been different in each full year shown. The average annual total return figures compare Class A, Class C and Class I share performance to the MSCI ACWI ex USA Growth Net Total Return USD Index, a market capitalization weighted index which includes growth companies in developed and emerging markets throughout the world, excluding the United States. Past performance (before and after taxes) is not necessarily an indication of how the Fund will perform in the future. The performance information shown is as of the calendar year ended December 31, 2021. Updated performance information may be obtained on the Thornburg website at Thornburg.com or by calling 1-800-847-0200.
Performance Information Illustrates Variability of Returns [Text] rr_PerformanceInformationIllustratesVariabilityOfReturns The following information provides some indication of the risks of investing in International Growth Fund by showing how the Fund’s investment results vary from year to year.
Performance Availability Phone [Text] rr_PerformanceAvailabilityPhone 1-800-847-0200
Performance Availability Website Address [Text] rr_PerformanceAvailabilityWebSiteAddress Thornburg.com
Performance Past Does Not Indicate Future [Text] rr_PerformancePastDoesNotIndicateFuture Past performance (before and after taxes) is not necessarily an indication of how the Fund will perform in the future.
Bar Chart [Heading] rr_BarChartHeading Annual Total Returns – Class A Shares
Bar Chart Does Not Reflect Sales Loads [Text] rr_BarChartDoesNotReflectSalesLoads The sales charge for Class A shares is not reflected in the returns shown on the bar chart, and the returns would be less if the charge was taken into account.
Bar Chart Closing [Text Block] rr_BarChartClosingTextBlock

Total
Returns

Quarter
ended

Highest Quarterly Results

25.93%

6/30/2020

Lowest Quarterly Results

(17.74)%

12/31/2018

The sales charge for Class A shares is not reflected in the returns shown on the bar chart, and the returns would be less if the charge was taken into account.
Performance Table Heading rr_PerformanceTableHeading Average Annual Total Returns (periods ended 12-31-21)
Performance Table Uses Highest Federal Rate rr_PerformanceTableUsesHighestFederalRate After-tax returns are calculated using the highest historical individual federal marginal income tax rates, and do not reflect state or local income taxes.
Performance Table Not Relevant to Tax Deferred rr_PerformanceTableNotRelevantToTaxDeferred Actual after-tax returns depend on an investor’s own tax situation and may differ from the returns shown, and after-tax returns shown are not relevant to investors who hold their Fund shares through tax-deferred arrangements, such as 401(k) plans or individual retirement accounts.
Performance Table One Class of after Tax Shown [Text] rr_PerformanceTableOneClassOfAfterTaxShown The after-tax returns shown relate only to Class A shares, and after-tax returns for other share classes will vary.
Performance Table Closing [Text Block] rr_PerformanceTableClosingTextBlock

After-tax returns are calculated using the highest historical individual federal marginal income tax rates, and do not reflect state or local income taxes. Actual after-tax returns depend on an investor’s own tax situation and may differ from the returns shown, and after-tax returns shown are not relevant to investors who hold their Fund shares through tax-deferred arrangements, such as 401(k) plans or individual retirement accounts. The after-tax returns shown relate only to Class A shares, and after-tax returns for other share classes will vary.
Retail | Thornburg International Growth Fund | Thornburg International Growth Fund - Class A  
Prospectus [Line Items] rr_ProspectusLineItems  
Trading Symbol dei_TradingSymbol TIGAX
Maximum Sales Charge Imposed on Purchases (as a percentage of Offering Price) rr_MaximumSalesChargeImposedOnPurchasesOverOfferingPrice 4.50%
Maximum Deferred Sales Charge (as a percentage) rr_MaximumDeferredSalesChargeOverOther none [11]
Management Fees (as a percentage of Assets) rr_ManagementFeesOverAssets 0.80%
Distribution and Service (12b-1) Fees rr_DistributionAndService12b1FeesOverAssets 0.25%
Other Expenses (as a percentage of Assets): rr_OtherExpensesOverAssets 0.21% [12]
Expenses (as a percentage of Assets) rr_ExpensesOverAssets 1.26%
Expense Example, with Redemption, 1 Year rr_ExpenseExampleYear01 $ 573
Expense Example, with Redemption, 3 Years rr_ExpenseExampleYear03 832
Expense Example, with Redemption, 5 Years rr_ExpenseExampleYear05 1,110
Expense Example, with Redemption, 10 Years rr_ExpenseExampleYear10 $ 1,904
Annual Return 2012 rr_AnnualReturn2012 21.87%
Annual Return 2013 rr_AnnualReturn2013 36.41%
Annual Return 2014 rr_AnnualReturn2014 (12.46%)
Annual Return 2015 rr_AnnualReturn2015 6.33%
Annual Return 2016 rr_AnnualReturn2016 (5.05%)
Annual Return 2017 rr_AnnualReturn2017 34.33%
Annual Return 2018 rr_AnnualReturn2018 (17.01%)
Annual Return 2019 rr_AnnualReturn2019 25.87%
Annual Return 2020 rr_AnnualReturn2020 33.94%
Annual Return 2021 rr_AnnualReturn2021 (4.46%)
Highest Quarterly Return, Label rr_HighestQuarterlyReturnLabel Highest Quarterly Results
Highest Quarterly Return, Date rr_BarChartHighestQuarterlyReturnDate Jun. 30, 2020
Highest Quarterly Return rr_BarChartHighestQuarterlyReturn 25.93%
Lowest Quarterly Return, Label rr_LowestQuarterlyReturnLabel Lowest Quarterly Results
Lowest Quarterly Return, Date rr_BarChartLowestQuarterlyReturnDate Dec. 31, 2018
Lowest Quarterly Return rr_BarChartLowestQuarterlyReturn (17.74%)
1 Year rr_AverageAnnualReturnYear01 (8.76%)
5 Years rr_AverageAnnualReturnYear05 11.39%
10 Years rr_AverageAnnualReturnYear10 9.68%
Retail | Thornburg International Growth Fund | Thornburg International Growth Fund - Class A | After Taxes on Distributions  
Prospectus [Line Items] rr_ProspectusLineItems  
1 Year rr_AverageAnnualReturnYear01 (10.17%)
5 Years rr_AverageAnnualReturnYear05 10.52%
10 Years rr_AverageAnnualReturnYear10 8.99%
Retail | Thornburg International Growth Fund | Thornburg International Growth Fund - Class A | After Taxes on Distributions and Sales  
Prospectus [Line Items] rr_ProspectusLineItems  
1 Year rr_AverageAnnualReturnYear01 (4.14%)
5 Years rr_AverageAnnualReturnYear05 8.93%
10 Years rr_AverageAnnualReturnYear10 7.78%
Retail | Thornburg International Growth Fund | Thornburg International Growth Fund - Class A | MSCI ACWI ex USA Growth Net Total Return USD Index (reflects no deduction for fees, expenses, or U.S. taxes)  
Prospectus [Line Items] rr_ProspectusLineItems  
1 Year rr_AverageAnnualReturnYear01 5.09%
5 Years rr_AverageAnnualReturnYear05 13.06%
10 Years rr_AverageAnnualReturnYear10 9.13%
Retail | Thornburg International Growth Fund | Thornburg International Growth Fund - Class C  
Prospectus [Line Items] rr_ProspectusLineItems  
Trading Symbol dei_TradingSymbol TIGCX
Maximum Sales Charge Imposed on Purchases (as a percentage of Offering Price) rr_MaximumSalesChargeImposedOnPurchasesOverOfferingPrice none
Maximum Deferred Sales Charge (as a percentage) rr_MaximumDeferredSalesChargeOverOther 1.00% [13]
Management Fees (as a percentage of Assets) rr_ManagementFeesOverAssets 0.80%
Distribution and Service (12b-1) Fees rr_DistributionAndService12b1FeesOverAssets 1.00%
Other Expenses (as a percentage of Assets): rr_OtherExpensesOverAssets 0.27% [12]
Expenses (as a percentage of Assets) rr_ExpensesOverAssets 2.07%
Expense Example, with Redemption, 1 Year rr_ExpenseExampleYear01 $ 310
Expense Example, with Redemption, 3 Years rr_ExpenseExampleYear03 649
Expense Example, with Redemption, 5 Years rr_ExpenseExampleYear05 1,114
Expense Example, with Redemption, 10 Years rr_ExpenseExampleYear10 2,400
Expense Example, No Redemption, 1 Year rr_ExpenseExampleNoRedemptionYear01 210
Expense Example, No Redemption, 3 Years rr_ExpenseExampleNoRedemptionYear03 649
Expense Example, No Redemption, 5 Years rr_ExpenseExampleNoRedemptionYear05 1,114
Expense Example, No Redemption, 10 Years rr_ExpenseExampleNoRedemptionYear10 $ 2,400
1 Year rr_AverageAnnualReturnYear01 (6.12%)
5 Years rr_AverageAnnualReturnYear05 11.56%
10 Years rr_AverageAnnualReturnYear10 9.34%
Retail | Thornburg International Growth Fund | Thornburg International Growth Fund - Class C | MSCI ACWI ex USA Growth Net Total Return USD Index (reflects no deduction for fees, expenses, or U.S. taxes)  
Prospectus [Line Items] rr_ProspectusLineItems  
1 Year rr_AverageAnnualReturnYear01 5.09%
5 Years rr_AverageAnnualReturnYear05 13.06%
10 Years rr_AverageAnnualReturnYear10 9.13%
Retail | Thornburg International Growth Fund | Thornburg International Growth Fund - Class I  
Prospectus [Line Items] rr_ProspectusLineItems  
Trading Symbol dei_TradingSymbol TINGX
Maximum Sales Charge Imposed on Purchases (as a percentage of Offering Price) rr_MaximumSalesChargeImposedOnPurchasesOverOfferingPrice none
Maximum Deferred Sales Charge (as a percentage) rr_MaximumDeferredSalesChargeOverOther none
Management Fees (as a percentage of Assets) rr_ManagementFeesOverAssets 0.80%
Distribution and Service (12b-1) Fees rr_DistributionAndService12b1FeesOverAssets none
Other Expenses (as a percentage of Assets): rr_OtherExpensesOverAssets 0.19% [12]
Expenses (as a percentage of Assets) rr_ExpensesOverAssets 0.99%
Expense Example, with Redemption, 1 Year rr_ExpenseExampleYear01 $ 101
Expense Example, with Redemption, 3 Years rr_ExpenseExampleYear03 315
Expense Example, with Redemption, 5 Years rr_ExpenseExampleYear05 547
Expense Example, with Redemption, 10 Years rr_ExpenseExampleYear10 $ 1,213
1 Year rr_AverageAnnualReturnYear01 (4.20%)
5 Years rr_AverageAnnualReturnYear05 12.80%
10 Years rr_AverageAnnualReturnYear10 10.60%
Retail | Thornburg International Growth Fund | Thornburg International Growth Fund - Class I | MSCI ACWI ex USA Growth Net Total Return USD Index (reflects no deduction for fees, expenses, or U.S. taxes)  
Prospectus [Line Items] rr_ProspectusLineItems  
1 Year rr_AverageAnnualReturnYear01 5.09%
5 Years rr_AverageAnnualReturnYear05 13.06%
10 Years rr_AverageAnnualReturnYear10 9.13%
Retail | Thornburg Developing World Fund  
Prospectus [Line Items] rr_ProspectusLineItems  
Risk/Return [Heading] rr_RiskReturnHeading Developing World Fund
Objective [Heading] rr_ObjectiveHeading Investment Goal
Objective, Primary [Text Block] rr_ObjectivePrimaryTextBlock

The Fund’s primary investment goal is long-term capital appreciation.

Expense [Heading] rr_ExpenseHeading Fees and Expenses of the Fund
Expense Narrative [Text Block] rr_ExpenseNarrativeTextBlock

This table describes the fees and expenses that you may pay if you buy and hold shares of the Fund. You may qualify for discounts from the sales charge applicable to Class A shares if you or other qualifying account holders invest, or agree to invest in the future, at least $50,000 in the Thornburg Funds. More information about this and other discounts and sales charge waivers is available from your financial intermediary, in the Prospectus under the captions “Class A Sales Charge Waivers,” beginning on page 146, and “Appendix A – Sales Charge Waivers Offered by Financial Intermediaries,” beginning on page 200, and in the Statement of Additional Information under the caption “Additional Information Respecting Purchase and Redemption of Shares,” beginning on page 108.
Shareholder Fees Caption [Text] rr_ShareholderFeesCaption Shareholder Fees (fees paid directly from your investment)
Operating Expenses Caption [Text] rr_OperatingExpensesCaption Annual Fund Operating Expenses (expenses that you pay each year as a percentage of the value of your investment)
Fee Waiver or Reimbursement over Assets, Date of Termination rr_FeeWaiverOrReimbursementOverAssetsDateOfTermination February 1, 2023
Portfolio Turnover [Heading] rr_PortfolioTurnoverHeading Portfolio Turnover.
Portfolio Turnover [Text Block] rr_PortfolioTurnoverTextBlock

The Fund pays transaction costs, such as commissions, when it buys and sells securities (or “turns over” its portfolio). A higher portfolio turnover rate may indicate higher transaction costs and may result in higher taxes when Fund shares are held in a taxable account. These costs, which are not reflected in Annual Fund Operating Expenses or in the Example, affect the Fund’s performance. During the most recent fiscal year, the Fund’s portfolio turnover rate was 61.50% of the average value of its portfolio.
Portfolio Turnover, Rate rr_PortfolioTurnoverRate 61.50%
Expense Breakpoint Discounts [Text] rr_ExpenseBreakpointDiscounts You may qualify for discounts from the sales charge applicable to Class A shares if you or other qualifying account holders invest, or agree to invest in the future, at least $50,000 in the Thornburg Funds.
Expense Breakpoint, Minimum Investment Required [Amount] rr_ExpenseBreakpointMinimumInvestmentRequiredAmount $ 50,000
Expense Example [Heading] rr_ExpenseExampleHeading Example.
Expense Example Narrative [Text Block] rr_ExpenseExampleNarrativeTextBlock

This Example is intended to help you compare the cost of investing in the Fund with the cost of investing in other mutual funds.

The Example assumes that you invest $10,000 in the Fund for the time periods indicated and then redeem all of your shares at the end of those periods. The Example also assumes that your investment has a 5% return each year, dividends and distributions are reinvested, and that the Fund’s operating expenses remain the same. Although your actual costs may be higher or lower, based on these assumptions (and giving effect to fee waivers and expense reimbursements in the first year), your costs would be:
Expense Example, No Redemption Narrative [Text Block] rr_ExpenseExampleNoRedemptionNarrativeTextBlock

You would pay the following expenses if you did not redeem your Class C shares:
Strategy [Heading] rr_StrategyHeading Principal Investment Strategies
Strategy Narrative [Text Block] rr_StrategyNarrativeTextBlock

Under normal market conditions the Fund invests at least 80% of its assets in equity securities of developing country issuers. A developing country issuer is a company or sovereign entity that is domiciled or otherwise tied economically to one or more developing countries. The Fund may invest in issuers of any size of capitalization, including small companies.

Currently, the Fund’s investment advisor, Thornburg Investment Management, Inc. (“Thornburg”) considers developing countries to include most Central and South American, African, Asian and Eastern European nations, including, but not limited to, Argentina, Austria, Brazil, Chile, China, Colombia, Czech Republic, Egypt, Greece, Hong Kong, Hungary, India, Indonesia, Israel, South Korea, Malaysia, Mexico, Morocco, Nigeria, Pakistan, Peru, Philippines, Poland, Qatar, Romania, the Russian Federation, Slovenia, South Africa, Taiwan, Thailand, Turkey, Ukraine, the United Arab Emirates and Vietnam. Thornburg identifies what it considers to be developing countries based upon its own analysis of measures of industrialization, economic growth, population growth and other factors, and may also consider classifications by the World Bank, the International Finance Corporation, the United Nations and independent financial services firms that maintain indices of developing countries.

Thornburg considers a variety of factors to determine whether an investment is tied economically to one or more developing countries, including (i) whether or not a significant portion of the issuer’s revenues or assets are derived from or are located in developing countries, (ii) the primary trading market of the issuer’s securities, (iii) the locations of its principal offices or operations, (iv) the source of any governmental guarantees or other supports, (v) identification of the issuer’s securities within an index or other listing indicating its location in a particular developing country or region, and (vi) the extent to which the investment is otherwise exposed to the economic fortunes and risks of developing countries.

The Fund expects that under normal conditions its assets will be invested in issuers domiciled in or tied economically to a variety of different countries.

The Fund’s policy of investing at least 80% of its assets in developing country issuers may be changed by the Fund’s Trustees without a shareholder vote upon 60 days’ notice to shareholders.

Among the specific factors considered in identifying securities for inclusion in the Fund are domestic and international economic developments, outlooks for securities markets, the supply and demand for equity securities, and analysis of specific issuers. The Fund typically makes its equity investments in the following three types of issuers:

Basic Value: Companies generally operating in mature or cyclical industries and which generally exhibit more economic sensitivity and/or higher volatility in earnings and cash flow.

Consistent Earner: Companies which generally exhibit predictable growth, profitability, cash flow and/or dividends.

Emerging Franchise: Companies with the potential to grow at an above average rate because of a product or service that is establishing a new market and/or taking share from existing participants.

Inclusion of any investment in any of the three described categories represents the opinion of the advisor concerning the characteristics and prospects of the investment. There is no assurance that any company selected for investment will, once categorized in one of the three described investment categories, continue to have the positive characteristics or fulfill the expectations that the advisor had for the company when it was selected for investment, and any such company may not grow or may decline in earnings and size.

The Fund may sell an investment if Thornburg has identified a better investment opportunity, in response to changes in the conditions or business of the investment’s issuer or changes in overall market conditions, if Thornburg has a target price for the investment and that target price has been achieved, or if, in Thornburg’s opinion, the investment no longer serves to achieve the Fund’s investment goals.
Risk [Heading] rr_RiskHeading Principal Investment Risks
Risk Narrative [Text Block] rr_RiskNarrativeTextBlock

An investment in the Fund is not a deposit in any bank and is not insured or guaranteed by the Federal Deposit Insurance Corporation or any other governmental agency. Accordingly, the loss of money is a risk of investing in the Fund. The value of the Fund’s shares varies from day to day and over time, and when you sell your shares they may be worth less than what you paid for them. The following is a summary of the principal risks of investing in the Fund.

Management Risk – The Fund is an actively managed portfolio, and the value of the Fund may be reduced if Thornburg pursues unsuccessful investments or fails to correctly identify risks affecting the broad economy or specific issuers in which the Fund invests.


Market and Economic Risk – The value of the Fund’s investments may decline and its share value may be reduced due to changes in general economic and market conditions. The value of a security may change in response to developments affecting entire economies, markets or industries, including changes in interest rates, political and legal developments, and general market volatility. These risks may be more pronounced for the Fund’s investments in developing countries.

Equity Risk – The value of the Fund’s equity investments may fluctuate significantly over time in response to factors affecting individual issuers, particular industries, or the market as a whole. Additionally, common stock ranks below preferred stock and debt securities in claims for dividends and for assets of a company in a liquidation or bankruptcy.

Risks Affecting Specific Issuers – The value of an equity security may decline in response to developments affecting the specific issuer of the security or obligation, even if the overall industry or economy is unaffected. These developments may include a variety of factors, including but not limited to management issues or other corporate disruption, a decline in revenues or profitability, an increase in costs, or an adverse effect on the issuer’s competitive position.

Foreign Investment Risk – Investments in securities of foreign issuers may involve risks including adverse fluctuations in currency exchange rates, political instability, confiscations, taxes or restrictions on currency exchange, difficulty in selling foreign investments, and reduced legal protections.

Developing Country Risk – The risks which may affect investments in foreign issuers (see “Foreign Investment Risk,” above) may be more pronounced for investments in developing countries because the economies of those countries are usually less diversified, communications, transportation and economic infrastructures are less developed, and developing countries ordinarily have less established legal, political, business and social frameworks. At times the prices of equity securities of a developing country issuer may be extremely volatile. An issuer domiciled in a developed country may be similarly affected by these developing country risks to the extent that the issuer conducts its business in developing countries.

Foreign Currency Risk – Fluctuations in currency exchange rates can adversely affect the value of the Fund’s foreign investments. Such fluctuations may occur for a number of reasons, including market and economic conditions, or a government’s decision to devalue its currency or impose currency controls.

Risks Affecting Specific Countries or Regions – If a significant portion of the Fund’s assets is invested in issuers that are economically exposed to one country or region, the Fund’s share value may be more susceptible to the conditions and developments in that country or region, and potentially more volatile than the share value of a more geographically diversified fund. A specific country or region could also be adversely affected by conditions or developments arising in other countries. For example, the U.S. government could take actions to prohibit or restrict individuals or companies within the U.S. from purchasing or holding the shares of issuers in another country, which may limit the Fund’s ability to invest in that country or cause the Fund to have to sell investments in that country at less than desired prices. The nature and degree of the risks affecting a given country or region, and the extent of the Fund’s exposure to any such country or region, is expected to vary over time.

Risks Affecting Investments in China – A significant portion of the Fund’s assets may be invested in companies exposed to China. Risks affecting investments in China include a potential downturn in the Chinese economy, reduced liquidity or increased price volatility in the Chinese securities markets as a result of trading suspensions affecting Chinese issuers or other factors, the potential that the Chinese government may expand restrictions on foreign investments or the repatriation of capital, and the implementation of new tariffs or other trade barriers by China or its trading partners. A lack of transparency respecting Chinese companies may also reduce the Fund’s ability to conduct diligence respecting those companies’ accounting and governance standards, which may in turn reduce the Fund’s ability to detect fraudulent practices that may adversely affect the companies’ stock prices.

Small and Mid-Cap Company Risk – Investments in small-capitalization companies and mid-capitalization companies may involve additional risks, which may be relatively higher with smaller companies. These additional risks may result from limited product lines, more limited access to markets and financial resources, greater vulnerability to competition and changes in markets, lack of management depth, increased volatility in share price, and possible difficulties in valuing or selling these investments.

Credit Risk – The inability of an issuer to pay principal and interest on its debt obligations when due, or the downgrading of an issuer’s debt obligations by ratings agencies, may adversely affect the market’s perceptions of the issuer’s financial strength and may therefore result in declines in the issuer’s stock price.

Liquidity Risk – Due to a lack of demand in the marketplace or other factors, the Fund may not be able to sell some or all of its investments promptly, or may only be able to sell investments at less than desired prices. This risk may be more pronounced for the Fund’s investments in developing countries.

Cybersecurity and Operational Risk – Operational failures, cyber-attacks or other disruptions that affect the Fund’s service providers, the Fund’s counterparties, other market participants or the issuers of securities held by the Fund may adversely affect the Fund and its shareholders, including by causing losses for the Fund or impairing Fund operations.

Additional information about Fund investments, investment strategies and risks of investing in the Fund appears beginning on page 118 of the Prospectus.
Risk Lose Money [Text] rr_RiskLoseMoney Accordingly, the loss of money is a risk of investing in the Fund.
RIsk Not Insured [Text] rr_RiskNotInsured An investment in the Fund is not a deposit in any bank and is not insured or guaranteed by the Federal Deposit Insurance Corporation or any other governmental agency.
Bar Chart and Performance Table [Heading] rr_BarChartAndPerformanceTableHeading Past Performance of the Fund
Performance Narrative [Text Block] rr_PerformanceNarrativeTextBlock

The following information provides some indication of the risks of investing in Developing World Fund by showing how the Fund’s investment results vary from year to year. The bar chart shows how the annual total returns for Class A shares have been different in each full year shown. The average annual total return figures compare Class A, Class C and Class I share performance to the MSCI Emerging Markets Net Total Return USD Index, which represents a broad measure of equity market performance of emerging markets. Past performance (before and after taxes) is not necessarily an indication of how the Fund will perform in the future. The performance information shown is as of the calendar year ended December 31, 2021. Updated performance information may be obtained on the Thornburg website at Thornburg.com or by calling 1-800-847-0200.
Performance Information Illustrates Variability of Returns [Text] rr_PerformanceInformationIllustratesVariabilityOfReturns The following information provides some indication of the risks of investing in Developing World Fund by showing how the Fund’s investment results vary from year to year.
Performance Availability Phone [Text] rr_PerformanceAvailabilityPhone 1-800-847-0200
Performance Availability Website Address [Text] rr_PerformanceAvailabilityWebSiteAddress Thornburg.com
Performance Past Does Not Indicate Future [Text] rr_PerformancePastDoesNotIndicateFuture Past performance (before and after taxes) is not necessarily an indication of how the Fund will perform in the future.
Bar Chart [Heading] rr_BarChartHeading Annual Total Returns – Class A Shares
Bar Chart Does Not Reflect Sales Loads [Text] rr_BarChartDoesNotReflectSalesLoads The sales charge for Class A shares is not reflected in the returns shown on the bar chart, and the returns would be less if the charge was taken into account.
Bar Chart Closing [Text Block] rr_BarChartClosingTextBlock

Total
Returns

Quarter
ended

Highest Quarterly Results

21.64%

12/31/2020

Lowest Quarterly Results

(24.81)%

3/31/2020

The sales charge for Class A shares is not reflected in the returns shown on the bar chart, and the returns would be less if the charge was taken into account.
Performance Table Heading rr_PerformanceTableHeading Average Annual Total Returns (periods ended 12-31-21)
Performance Table Uses Highest Federal Rate rr_PerformanceTableUsesHighestFederalRate fter-tax returns are calculated using the historical highest individual federal marginal income tax rates, and do not reflect state or local income taxes.
Performance Table Not Relevant to Tax Deferred rr_PerformanceTableNotRelevantToTaxDeferred Actual after-tax returns depend on an investor’s own tax situation and may differ from the returns shown, and after-tax returns shown are not relevant to investors who hold their Fund shares through tax-deferred arrangements, such as 401(k) plans or individual retirement accounts.
Performance Table One Class of after Tax Shown [Text] rr_PerformanceTableOneClassOfAfterTaxShown The after-tax returns shown relate only to Class A shares, and after-tax returns for other share classes will vary.
Performance Table Closing [Text Block] rr_PerformanceTableClosingTextBlock

After-tax returns are calculated using the historical highest individual federal marginal income tax rates, and do not reflect state or local income taxes. Actual after-tax returns depend on an investor’s own tax situation and may differ from the returns shown, and after-tax returns shown are not relevant to investors who hold their Fund shares through tax-deferred arrangements, such as 401(k) plans or individual retirement accounts. The after-tax returns shown relate only to Class A shares, and after-tax returns for other share classes will vary.
Retail | Thornburg Developing World Fund | Thornburg Developing World Fund Class A  
Prospectus [Line Items] rr_ProspectusLineItems  
Trading Symbol dei_TradingSymbol THDAX
Maximum Sales Charge Imposed on Purchases (as a percentage of Offering Price) rr_MaximumSalesChargeImposedOnPurchasesOverOfferingPrice 4.50%
Maximum Deferred Sales Charge (as a percentage) rr_MaximumDeferredSalesChargeOverOther none [14]
Management Fees (as a percentage of Assets) rr_ManagementFeesOverAssets 0.94%
Distribution and Service (12b-1) Fees rr_DistributionAndService12b1FeesOverAssets 0.25%
Other Expenses (as a percentage of Assets): rr_OtherExpensesOverAssets 0.24%
Expenses (as a percentage of Assets) rr_ExpensesOverAssets 1.43%
Fee Waiver or Reimbursement rr_FeeWaiverOrReimbursementOverAssets
Net Expenses (as a percentage of Assets) rr_NetExpensesOverAssets 1.43%
Expense Example, with Redemption, 1 Year rr_ExpenseExampleYear01 $ 589
Expense Example, with Redemption, 3 Years rr_ExpenseExampleYear03 882
Expense Example, with Redemption, 5 Years rr_ExpenseExampleYear05 1,196
Expense Example, with Redemption, 10 Years rr_ExpenseExampleYear10 $ 2,086
Annual Return 2012 rr_AnnualReturn2012 22.70%
Annual Return 2013 rr_AnnualReturn2013 15.61%
Annual Return 2014 rr_AnnualReturn2014 (3.04%)
Annual Return 2015 rr_AnnualReturn2015 (15.34%)
Annual Return 2016 rr_AnnualReturn2016 2.55%
Annual Return 2017 rr_AnnualReturn2017 35.31%
Annual Return 2018 rr_AnnualReturn2018 (15.18%)
Annual Return 2019 rr_AnnualReturn2019 29.03%
Annual Return 2020 rr_AnnualReturn2020 22.66%
Annual Return 2021 rr_AnnualReturn2021 (3.01%)
Highest Quarterly Return, Label rr_HighestQuarterlyReturnLabel Highest Quarterly Results
Highest Quarterly Return, Date rr_BarChartHighestQuarterlyReturnDate Dec. 31, 2020
Highest Quarterly Return rr_BarChartHighestQuarterlyReturn 21.64%
Lowest Quarterly Return, Label rr_LowestQuarterlyReturnLabel Lowest Quarterly Results
Lowest Quarterly Return, Date rr_BarChartLowestQuarterlyReturnDate Mar. 31, 2020
Lowest Quarterly Return rr_BarChartLowestQuarterlyReturn (24.81%)
1 Year rr_AverageAnnualReturnYear01 (7.37%)
5 Years rr_AverageAnnualReturnYear05 10.97%
10 Years rr_AverageAnnualReturnYear10 7.23%
Retail | Thornburg Developing World Fund | Thornburg Developing World Fund Class A | After Taxes on Distributions  
Prospectus [Line Items] rr_ProspectusLineItems  
1 Year rr_AverageAnnualReturnYear01 (7.37%)
5 Years rr_AverageAnnualReturnYear05 10.75%
10 Years rr_AverageAnnualReturnYear10 7.10%
Retail | Thornburg Developing World Fund | Thornburg Developing World Fund Class A | After Taxes on Distributions and Sales  
Prospectus [Line Items] rr_ProspectusLineItems  
1 Year rr_AverageAnnualReturnYear01 (4.36%)
5 Years rr_AverageAnnualReturnYear05 8.62%
10 Years rr_AverageAnnualReturnYear10 5.80%
Retail | Thornburg Developing World Fund | Thornburg Developing World Fund Class A | MSCI Emerging Markets Net Total Return USD Index (reflects no deduction for fees, expenses, or U.S. taxes)  
Prospectus [Line Items] rr_ProspectusLineItems  
1 Year rr_AverageAnnualReturnYear01 (2.54%)
5 Years rr_AverageAnnualReturnYear05 9.87%
10 Years rr_AverageAnnualReturnYear10 5.49%
Retail | Thornburg Developing World Fund | Thornburg Developing World Fund Class C  
Prospectus [Line Items] rr_ProspectusLineItems  
Trading Symbol dei_TradingSymbol THDCX
Maximum Sales Charge Imposed on Purchases (as a percentage of Offering Price) rr_MaximumSalesChargeImposedOnPurchasesOverOfferingPrice none
Maximum Deferred Sales Charge (as a percentage) rr_MaximumDeferredSalesChargeOverOther 1.00% [15]
Management Fees (as a percentage of Assets) rr_ManagementFeesOverAssets 0.94%
Distribution and Service (12b-1) Fees rr_DistributionAndService12b1FeesOverAssets 1.00%
Other Expenses (as a percentage of Assets): rr_OtherExpensesOverAssets 0.25%
Expenses (as a percentage of Assets) rr_ExpensesOverAssets 2.19%
Fee Waiver or Reimbursement rr_FeeWaiverOrReimbursementOverAssets
Net Expenses (as a percentage of Assets) rr_NetExpensesOverAssets 2.19%
Expense Example, with Redemption, 1 Year rr_ExpenseExampleYear01 $ 322
Expense Example, with Redemption, 3 Years rr_ExpenseExampleYear03 685
Expense Example, with Redemption, 5 Years rr_ExpenseExampleYear05 1,175
Expense Example, with Redemption, 10 Years rr_ExpenseExampleYear10 2,524
Expense Example, No Redemption, 1 Year rr_ExpenseExampleNoRedemptionYear01 222
Expense Example, No Redemption, 3 Years rr_ExpenseExampleNoRedemptionYear03 685
Expense Example, No Redemption, 5 Years rr_ExpenseExampleNoRedemptionYear05 1,175
Expense Example, No Redemption, 10 Years rr_ExpenseExampleNoRedemptionYear10 $ 2,524
1 Year rr_AverageAnnualReturnYear01 (4.72%)
5 Years rr_AverageAnnualReturnYear05 11.14%
10 Years rr_AverageAnnualReturnYear10 6.90%
Retail | Thornburg Developing World Fund | Thornburg Developing World Fund Class C | MSCI Emerging Markets Net Total Return USD Index (reflects no deduction for fees, expenses, or U.S. taxes)  
Prospectus [Line Items] rr_ProspectusLineItems  
1 Year rr_AverageAnnualReturnYear01 (2.54%)
5 Years rr_AverageAnnualReturnYear05 9.87%
10 Years rr_AverageAnnualReturnYear10 5.49%
Retail | Thornburg Developing World Fund | Thornburg Developing World Fund Class I  
Prospectus [Line Items] rr_ProspectusLineItems  
Trading Symbol dei_TradingSymbol THDIX
Maximum Sales Charge Imposed on Purchases (as a percentage of Offering Price) rr_MaximumSalesChargeImposedOnPurchasesOverOfferingPrice none
Maximum Deferred Sales Charge (as a percentage) rr_MaximumDeferredSalesChargeOverOther none
Management Fees (as a percentage of Assets) rr_ManagementFeesOverAssets 0.94%
Distribution and Service (12b-1) Fees rr_DistributionAndService12b1FeesOverAssets none
Other Expenses (as a percentage of Assets): rr_OtherExpensesOverAssets 0.21%
Expenses (as a percentage of Assets) rr_ExpensesOverAssets 1.15%
Fee Waiver or Reimbursement rr_FeeWaiverOrReimbursementOverAssets (0.11%) [16]
Net Expenses (as a percentage of Assets) rr_NetExpensesOverAssets 1.04%
Expense Example, with Redemption, 1 Year rr_ExpenseExampleYear01 $ 106
Expense Example, with Redemption, 3 Years rr_ExpenseExampleYear03 354
Expense Example, with Redemption, 5 Years rr_ExpenseExampleYear05 622
Expense Example, with Redemption, 10 Years rr_ExpenseExampleYear10 $ 1,388
1 Year rr_AverageAnnualReturnYear01 (2.67%)
5 Years rr_AverageAnnualReturnYear05 12.41%
10 Years rr_AverageAnnualReturnYear10 8.17%
Retail | Thornburg Developing World Fund | Thornburg Developing World Fund Class I | MSCI Emerging Markets Net Total Return USD Index (reflects no deduction for fees, expenses, or U.S. taxes)  
Prospectus [Line Items] rr_ProspectusLineItems  
1 Year rr_AverageAnnualReturnYear01 (2.54%)
5 Years rr_AverageAnnualReturnYear05 9.87%
10 Years rr_AverageAnnualReturnYear10 5.49%
Retail | Thornburg Small/Mid Cap Core Fund  
Prospectus [Line Items] rr_ProspectusLineItems  
Risk/Return [Heading] rr_RiskReturnHeading Small/Mid Cap Core Fund
Objective [Heading] rr_ObjectiveHeading Investment Goal
Objective, Primary [Text Block] rr_ObjectivePrimaryTextBlock

The Fund seeks long-term capital appreciation by investing in equity and debt securities of all types.
Objective, Secondary [Text Block] rr_ObjectiveSecondaryTextBlock

The secondary, non-fundamental goal of the Fund is to seek some current income.
Expense [Heading] rr_ExpenseHeading Fees and Expenses of the Fund
Expense Narrative [Text Block] rr_ExpenseNarrativeTextBlock

This table describes the fees and expenses that you may pay if you buy and hold shares of the Fund. You may qualify for discounts from the sales charges applicable to Class A shares if you or other qualifying account holders invest, or agree to invest in the future, at least $50,000 in the Thornburg Funds. More information about this and other discounts and sales charge waivers is available from your financial intermediary, in the Prospectus under the captions “Class A Sales Charge Waivers,” beginning on page 146, and “Appendix A – Sales Charge Waivers Offered by Financial Intermediaries,” beginning on page 200, and in the Statement of Additional Information under the caption “Additional Information Respecting Purchase and Redemption of Shares,” beginning on page 108.
Shareholder Fees Caption [Text] rr_ShareholderFeesCaption Shareholder Fees (fees paid directly from your investment)
Operating Expenses Caption [Text] rr_OperatingExpensesCaption Annual Fund Operating Expenses (expenses that you pay each year as a percentage of the value of your investment)
Fee Waiver or Reimbursement over Assets, Date of Termination rr_FeeWaiverOrReimbursementOverAssetsDateOfTermination February 1, 2023
Portfolio Turnover [Heading] rr_PortfolioTurnoverHeading Portfolio Turnover.
Portfolio Turnover [Text Block] rr_PortfolioTurnoverTextBlock

The Fund pays transaction costs, such as commissions, when it buys and sells securities (or “turns over”) its portfolio. A higher portfolio turnover rate may indicate higher transaction costs and may result in higher taxes when Fund shares are held in a taxable account. These costs, which are not reflected in Annual Fund Operating Expenses or in the Example, affect the Fund’s performance. During the most recent fiscal year, the Fund’s portfolio turnover rate was 135.80% of the average value of its portfolio.
Portfolio Turnover, Rate rr_PortfolioTurnoverRate 135.80%
Expense Breakpoint Discounts [Text] rr_ExpenseBreakpointDiscounts You may qualify for discounts from the sales charges applicable to Class A shares if you or other qualifying account holders invest, or agree to invest in the future, at least $50,000 in the Thornburg Funds.
Expense Breakpoint, Minimum Investment Required [Amount] rr_ExpenseBreakpointMinimumInvestmentRequiredAmount $ 50,000
Expense Example [Heading] rr_ExpenseExampleHeading Example.
Expense Example Narrative [Text Block] rr_ExpenseExampleNarrativeTextBlock

This Example is intended to help you compare the cost of investing in the Fund with the cost of investing in other mutual funds.

The Example assumes that you invest $10,000 in the Fund for the time periods indicated and then redeem all of your shares at the end of those periods. The Example also assumes that your investment has a 5% return each year, dividends and distributions are reinvested, and that the Fund’s operating expenses remain the same. Although your actual costs may be higher or lower, based on these assumptions (and giving effect to fee waivers and expense reimbursements in the first year), your costs would be:
Expense Example, No Redemption Narrative [Text Block] rr_ExpenseExampleNoRedemptionNarrativeTextBlock

You would pay the following expenses if you did not redeem your Class C shares:
Strategy [Heading] rr_StrategyHeading Principal Investment Strategies
Strategy Narrative [Text Block] rr_StrategyNarrativeTextBlock

Under normal conditions, the Fund invests at least 80% of its net assets in small- and mid-capitalization companies. The Fund currently defines small- and mid-capitalization companies to be those within the market capitalization range comprised by the Russell 2500 Index – Total Return. As of November 30, 2021, the market capitalization range of the Russell 2500 Index – Total Return was approximately $14 million to $33 billion. The market capitalization range of the Russell 2500 Index – Total Return changes over time and, as a result, the capitalization range of companies in which the Fund invests will also change. The Fund may change the definition of what constitutes “small- and mid-capitalization companies” without advance notice to shareholders.

The Fund expects to invest primarily in domestic common stocks. However, the Fund may own foreign common stocks which, in the opinion of the Fund’s investment advisor, Thornburg Investment Management, Inc. (“Thornburg”), offer prospects for meeting the Fund’s investment goals.

With its core approach to stock selection, the Fund seeks to invest in a broadly diversified portfolio of companies the Fund categorizes as basic values, consistent earners, and emerging franchises, as described in more detail below. The relative proportions of securities invested in each of those categories will vary over time.

Thornburg primarily takes a bottom-up, fundamental view in determining the attractiveness of individual securities and in making investment decisions. Among the specific factors considered by Thornburg in identifying securities for inclusion in the Fund are:

•earnings growth potential

•durable business model

•industry growth potential

•innovation driving the potential to disrupt entrenched competitors

•intrinsic value appreciation potential

•potential size of addressable market

•management strength

•leverage

•return on invested capital

•valuation metrics, including: price/earnings (“PE”) ratio; enterprise value/revenue ratio; PE/growth rate ratio, enterprise value/EBITDA (earnings before interest, taxes, depreciation and amortization) ratio; and free cash flow yield.

The Fund categorizes its investments in the following three categories:

Basic Value: Companies generally operating in mature or cyclical industries and which generally exhibit more economic sensitivity and/or higher volatility in earnings and cash flow.

Consistent Earner: Companies which generally exhibit predictable growth and profitability, and consistent cash flow and/or dividends.

Emerging Franchise: Companies with the potential to grow at an above average rate because of a product or service that is establishing a new market and/or taking share from existing participants.

Inclusion of any investment in any of the three described categories represents the opinion of the advisor concerning the characteristics and prospects of the investment. There is no assurance that any company selected for investment will, once categorized in one of the three described investment categories, continue to have the positive characteristics or fulfill the expectations that the advisor had for the company when it was selected for investment, and any such company may not grow or may decline in earnings and size.

The Fund selects foreign securities issued by companies domiciled in countries whose currencies are freely convertible into U.S. dollars, or in companies in other countries whose business is conducted primarily in U.S. dollars.

The Fund may sell an investment if Thornburg has identified a better investment opportunity, in response to changes in the conditions or business of the investment’s issuer or changes in overall market conditions, if Thornburg has a target price for the investment and that target price has been achieved, or if, in Thornburg’s opinion, the investment no longer serves to achieve the Fund’s investment goals.

The Fund’s policy of investing at least 80% of its assets in small- and mid-capitalization companies may be changed by the Fund’s Trustees without a shareholder vote upon 60 days’ notice to shareholders.
Risk [Heading] rr_RiskHeading Principal Investment Risks
Risk Narrative [Text Block] rr_RiskNarrativeTextBlock

An investment in the Fund is not a deposit in any bank and is not insured or guaranteed by the Federal Deposit Insurance Corporation or any other governmental agency. Accordingly, the loss of money is a risk of investing in the Fund. The value of the Fund’s shares varies from day to day and over time, and when you sell your shares they may be worth less than what you paid for them. The following is a summary of the principal risks of investing in the Fund.

Management Risk – The Fund is an actively managed portfolio, and the value of the Fund may be reduced if Thornburg pursues unsuccessful investments or fails to correctly identify risks affecting the broad economy or specific issuers in which the Fund invests.

Market and Economic Risk – The value of the Fund’s investments may decline and its share value may be reduced due to changes in general economic and market conditions. The value of a security may change in response to developments affecting entire economies, markets or industries, including changes in interest rates, political and legal developments, and general market volatility.

Equity Risk – The value of the Fund’s equity investments may fluctuate significantly over time in response to factors affecting individual issuers, particular industries, or the market as a whole. Additionally, common stock ranks below preferred stock and debt securities in claims for dividends and for assets of a company in a liquidation or bankruptcy.

Risks Affecting Specific Issuers – The value of a security may decline in response to developments affecting the specific issuer of the security, even if the overall industry or economy is unaffected. These developments may include a variety of factors, including but not limited to management issues or other corporate disruption, a decline in revenues or profitability, an increase in costs, or an adverse effect on the issuer’s competitive position.

Small and Mid-Cap Company Risk – Investments in small-capitalization companies and mid-capitalization companies may involve additional risks, which may be relatively higher with smaller companies. These additional risks may result from limited product lines, earlier stages of development and lack of well-established businesses, more limited access to markets

and financial resources, greater vulnerability to competition and market risks and fluctuations, lack of management depth, increased volatility in share price, and possible difficulties in valuing or selling these investments. Relative to the stocks of large capitalization companies, the stocks of small- and mid-capitalization companies may be thinly traded and sales may result in higher transaction costs. Also, small- and mid-capitalization companies may perform poorly during times of economic stress.

Foreign Investment Risk – Investments in securities of foreign issuers may involve risks including adverse fluctuations in currency exchange rates, political instability, confiscations, taxes or restrictions on currency exchange, difficulty in selling foreign investments, and reduced legal protection.

Liquidity Risk – Due to a lack of demand in the marketplace or other factors, the Fund may not be able to sell some or all of its investments promptly, or may only be able to sell investments at less than desired prices.

Cybersecurity and Operational Risk – Operational failures, cyber-attacks or other disruptions that affect the Fund’s service providers, the Fund’s counterparties, other market participants or the issuers of securities held by the Fund may adversely affect the Fund and its shareholders, including by causing losses for the Fund or impairing Fund operations.

Additional information about Fund investments, investment strategies, and risks of investing in the Fund appears below beginning on page 118 of the Prospectus.
Risk Lose Money [Text] rr_RiskLoseMoney Accordingly, the loss of money is a risk of investing in the Fund.
RIsk Not Insured [Text] rr_RiskNotInsured An investment in the Fund is not a deposit in any bank and is not insured or guaranteed by the Federal Deposit Insurance Corporation or any other governmental agency.
Bar Chart and Performance Table [Heading] rr_BarChartAndPerformanceTableHeading Past Performance of the Fund
Performance Narrative [Text Block] rr_PerformanceNarrativeTextBlock

The following information provides some indication of the risks of investing in the Small/Mid Cap Core Fund by showing how the Fund’s investment results vary from year to year. The bar chart shows how the annual total returns for Class A shares have been different in each full year shown. The average annual total return figures compare Class A, Class C and Class I share performance to the Russell 2500 Index—Total Return, a broad measure of market performance. Past performance (before and after taxes) is not necessarily an indication of how the Fund will perform in the future. The performance information shown is as of the calendar year ended December 31, 2021. Updated performance information may be obtained on the Thornburg website at Thornburg.com or by calling 1-800-847-0200.

Performance Information Illustrates Variability of Returns [Text] rr_PerformanceInformationIllustratesVariabilityOfReturns The following information provides some indication of the risks of investing in the Small/Mid Cap Core Fund by showing how the Fund’s investment results vary from year to year.
Performance Availability Phone [Text] rr_PerformanceAvailabilityPhone 1-800-847-0200
Performance Availability Website Address [Text] rr_PerformanceAvailabilityWebSiteAddress Thornburg.com
Performance Past Does Not Indicate Future [Text] rr_PerformancePastDoesNotIndicateFuture Past performance (before and after taxes) is not necessarily an indication of how the Fund will perform in the future.
Bar Chart [Heading] rr_BarChartHeading Annual Total Returns – Class A Shares
Bar Chart Does Not Reflect Sales Loads [Text] rr_BarChartDoesNotReflectSalesLoads The sales charge for Class A shares is not reflected in the returns shown in the bar chart, and the returns would be less if the charge was taken into account.
Bar Chart Closing [Text Block] rr_BarChartClosingTextBlock

Total
Returns

Quarter
ended

Highest Quarterly Results

18.89%

6/30/2020

Lowest Quarterly Results

(26.30)%

3/31/2020

The sales charge for Class A shares is not reflected in the returns shown in the bar chart, and the returns would be less if the charge was taken into account.
Performance Table Heading rr_PerformanceTableHeading Average Annual Total Returns (periods ended 12-31-21)
Performance Table Uses Highest Federal Rate rr_PerformanceTableUsesHighestFederalRate fter-tax returns are calculated using the highest historical individual federal marginal income tax rates, and do not reflect state or local income taxes.
Performance Table Not Relevant to Tax Deferred rr_PerformanceTableNotRelevantToTaxDeferred Actual after-tax returns depend on an investor’s own tax situation and may differ from the returns shown, and after-tax returns shown are not relevant to investors who hold their Fund shares through tax-deferred arrangements, such as 401(k) plans or individual retirement accounts.
Performance Table One Class of after Tax Shown [Text] rr_PerformanceTableOneClassOfAfterTaxShown The after-tax returns shown relate only to Class A shares, and after-tax returns for other share classes will vary.
Performance Table Closing [Text Block] rr_PerformanceTableClosingTextBlock

After-tax returns are calculated using the highest historical individual federal marginal income tax rates, and do not reflect state or local income taxes. Actual after-tax returns depend on an investor’s own tax situation and may differ from the returns shown, and after-tax returns shown are not relevant to investors who hold their Fund shares through tax-deferred arrangements, such as 401(k) plans or individual retirement accounts. The after-tax returns shown relate only to Class A shares, and after-tax returns for other share classes will vary.

The performance information shown above may include gains attributable to the Fund’s investments in shares of companies through initial public offerings (“IPOs”). There can be no assurance that the Fund will have continued access to profitable IPOs and, as the Fund’s assets grow, the impact of the Fund’s investment in IPOs on the performance of the Fund may decline.
Retail | Thornburg Small/Mid Cap Core Fund | Thornburg Small/Mid Cap Core Fund - Class A  
Prospectus [Line Items] rr_ProspectusLineItems  
Trading Symbol dei_TradingSymbol TVAFX
Maximum Sales Charge Imposed on Purchases (as a percentage of Offering Price) rr_MaximumSalesChargeImposedOnPurchasesOverOfferingPrice 4.50%
Maximum Deferred Sales Charge (as a percentage) rr_MaximumDeferredSalesChargeOverOther none [17]
Management Fees (as a percentage of Assets) rr_ManagementFeesOverAssets 0.85%
Distribution and Service (12b-1) Fees rr_DistributionAndService12b1FeesOverAssets 0.25%
Other Expenses (as a percentage of Assets): rr_OtherExpensesOverAssets 0.21% [18]
Expenses (as a percentage of Assets) rr_ExpensesOverAssets 1.31%
Fee Waiver or Reimbursement rr_FeeWaiverOrReimbursementOverAssets
Net Expenses (as a percentage of Assets) rr_NetExpensesOverAssets 1.31%
Expense Example, with Redemption, 1 Year rr_ExpenseExampleYear01 $ 577
Expense Example, with Redemption, 3 Years rr_ExpenseExampleYear03 847
Expense Example, with Redemption, 5 Years rr_ExpenseExampleYear05 1,136
Expense Example, with Redemption, 10 Years rr_ExpenseExampleYear10 $ 1,958
Annual Return 2012 rr_AnnualReturn2012 10.65%
Annual Return 2013 rr_AnnualReturn2013 39.49%
Annual Return 2014 rr_AnnualReturn2014 11.50%
Annual Return 2015 rr_AnnualReturn2015 3.41%
Annual Return 2016 rr_AnnualReturn2016 6.60%
Annual Return 2017 rr_AnnualReturn2017 23.33%
Annual Return 2018 rr_AnnualReturn2018 (9.69%)
Annual Return 2019 rr_AnnualReturn2019 28.88%
Annual Return 2020 rr_AnnualReturn2020 11.71%
Annual Return 2021 rr_AnnualReturn2021 13.83%
Highest Quarterly Return, Label rr_HighestQuarterlyReturnLabel Highest Quarterly Results
Highest Quarterly Return, Date rr_BarChartHighestQuarterlyReturnDate Jun. 30, 2020
Highest Quarterly Return rr_BarChartHighestQuarterlyReturn 18.89%
Lowest Quarterly Return, Label rr_LowestQuarterlyReturnLabel Lowest Quarterly Results
Lowest Quarterly Return, Date rr_BarChartLowestQuarterlyReturnDate Mar. 31, 2020
Lowest Quarterly Return rr_BarChartLowestQuarterlyReturn (26.30%)
1 Year rr_AverageAnnualReturnYear01 8.70%
5 Years rr_AverageAnnualReturnYear05 11.75%
10 Years rr_AverageAnnualReturnYear10 12.70%
Retail | Thornburg Small/Mid Cap Core Fund | Thornburg Small/Mid Cap Core Fund - Class A | After Taxes on Distributions  
Prospectus [Line Items] rr_ProspectusLineItems  
1 Year rr_AverageAnnualReturnYear01 0.39%
5 Years rr_AverageAnnualReturnYear05 9.88%
10 Years rr_AverageAnnualReturnYear10 11.71%
Retail | Thornburg Small/Mid Cap Core Fund | Thornburg Small/Mid Cap Core Fund - Class A | After Taxes on Distributions and Sales  
Prospectus [Line Items] rr_ProspectusLineItems  
1 Year rr_AverageAnnualReturnYear01 8.70%
5 Years rr_AverageAnnualReturnYear05 9.01%
10 Years rr_AverageAnnualReturnYear10 10.44%
Retail | Thornburg Small/Mid Cap Core Fund | Thornburg Small/Mid Cap Core Fund - Class A | Russell 2500 Index-Total Return (reflects no deduction for fees, expenses, or taxes)  
Prospectus [Line Items] rr_ProspectusLineItems  
1 Year rr_AverageAnnualReturnYear01 18.18%
5 Years rr_AverageAnnualReturnYear05 13.75%
10 Years rr_AverageAnnualReturnYear10 14.15%
Retail | Thornburg Small/Mid Cap Core Fund | Thornburg Small/Mid Cap Core Fund - Class C  
Prospectus [Line Items] rr_ProspectusLineItems  
Trading Symbol dei_TradingSymbol TVCFX
Maximum Sales Charge Imposed on Purchases (as a percentage of Offering Price) rr_MaximumSalesChargeImposedOnPurchasesOverOfferingPrice none
Maximum Deferred Sales Charge (as a percentage) rr_MaximumDeferredSalesChargeOverOther 1.00% [19]
Management Fees (as a percentage of Assets) rr_ManagementFeesOverAssets 0.85%
Distribution and Service (12b-1) Fees rr_DistributionAndService12b1FeesOverAssets 1.00%
Other Expenses (as a percentage of Assets): rr_OtherExpensesOverAssets 0.28% [18]
Expenses (as a percentage of Assets) rr_ExpensesOverAssets 2.13%
Fee Waiver or Reimbursement rr_FeeWaiverOrReimbursementOverAssets
Net Expenses (as a percentage of Assets) rr_NetExpensesOverAssets 2.13%
Expense Example, with Redemption, 1 Year rr_ExpenseExampleYear01 $ 316
Expense Example, with Redemption, 3 Years rr_ExpenseExampleYear03 667
Expense Example, with Redemption, 5 Years rr_ExpenseExampleYear05 1,144
Expense Example, with Redemption, 10 Years rr_ExpenseExampleYear10 2,462
Expense Example, No Redemption, 1 Year rr_ExpenseExampleNoRedemptionYear01 216
Expense Example, No Redemption, 3 Years rr_ExpenseExampleNoRedemptionYear03 667
Expense Example, No Redemption, 5 Years rr_ExpenseExampleNoRedemptionYear05 1,144
Expense Example, No Redemption, 10 Years rr_ExpenseExampleNoRedemptionYear10 $ 2,462
1 Year rr_AverageAnnualReturnYear01 12.10%
5 Years rr_AverageAnnualReturnYear05 11.88%
10 Years rr_AverageAnnualReturnYear10 12.34%
Retail | Thornburg Small/Mid Cap Core Fund | Thornburg Small/Mid Cap Core Fund - Class C | Russell 2500 Index-Total Return (reflects no deduction for fees, expenses, or taxes)  
Prospectus [Line Items] rr_ProspectusLineItems  
1 Year rr_AverageAnnualReturnYear01 18.18%
5 Years rr_AverageAnnualReturnYear05 13.75%
10 Years rr_AverageAnnualReturnYear10 14.15%
Retail | Thornburg Small/Mid Cap Core Fund | Thornburg Small/Mid Cap Core Fund - Class I  
Prospectus [Line Items] rr_ProspectusLineItems  
Trading Symbol dei_TradingSymbol TVIFX
Maximum Sales Charge Imposed on Purchases (as a percentage of Offering Price) rr_MaximumSalesChargeImposedOnPurchasesOverOfferingPrice none
Maximum Deferred Sales Charge (as a percentage) rr_MaximumDeferredSalesChargeOverOther none
Management Fees (as a percentage of Assets) rr_ManagementFeesOverAssets 0.85%
Distribution and Service (12b-1) Fees rr_DistributionAndService12b1FeesOverAssets none
Other Expenses (as a percentage of Assets): rr_OtherExpensesOverAssets 0.21% [18]
Expenses (as a percentage of Assets) rr_ExpensesOverAssets 1.06%
Fee Waiver or Reimbursement rr_FeeWaiverOrReimbursementOverAssets (0.11%) [20]
Net Expenses (as a percentage of Assets) rr_NetExpensesOverAssets 0.95%
Expense Example, with Redemption, 1 Year rr_ExpenseExampleYear01 $ 97
Expense Example, with Redemption, 3 Years rr_ExpenseExampleYear03 326
Expense Example, with Redemption, 5 Years rr_ExpenseExampleYear05 574
Expense Example, with Redemption, 10 Years rr_ExpenseExampleYear10 $ 1,284
1 Year rr_AverageAnnualReturnYear01 14.18%
5 Years rr_AverageAnnualReturnYear05 13.17%
10 Years rr_AverageAnnualReturnYear10 13.64%
Retail | Thornburg Small/Mid Cap Core Fund | Thornburg Small/Mid Cap Core Fund - Class I | Russell 2500 Index-Total Return (reflects no deduction for fees, expenses, or taxes)  
Prospectus [Line Items] rr_ProspectusLineItems  
1 Year rr_AverageAnnualReturnYear01 18.18%
5 Years rr_AverageAnnualReturnYear05 13.75%
10 Years rr_AverageAnnualReturnYear10 14.15%
Retail | Thornburg Small/Mid Cap Growth Fund  
Prospectus [Line Items] rr_ProspectusLineItems  
Risk/Return [Heading] rr_RiskReturnHeading Small/Mid Cap Growth Fund
Objective [Heading] rr_ObjectiveHeading Investment Goal
Objective, Primary [Text Block] rr_ObjectivePrimaryTextBlock

The Fund seeks long-term growth of capital by investing in equity securities selected for their growth potential.

Expense [Heading] rr_ExpenseHeading Fees and Expenses of the Fund
Expense Narrative [Text Block] rr_ExpenseNarrativeTextBlock

This table describes the fees and expenses that you may pay if you buy and hold shares of the Fund. You may qualify for discounts from the sales charges applicable to Class A shares if you or other qualifying account holders invest, or agree to invest in the future, at least $50,000 in the Thornburg Funds. More information about this and other discounts and sales charge waivers is available from your financial intermediary, in the Prospectus under the captions “Class A Sales Charge Waivers,” beginning on page 146, and “Appendix A – Sales Charge Waivers Offered by Financial Intermediaries,” beginning on page 200, and in the Statement of Additional Information under the caption “Additional Information Respecting Purchase and Redemption of Shares,” beginning on page 108.
Shareholder Fees Caption [Text] rr_ShareholderFeesCaption Shareholder Fees (fees paid directly from your investment)
Operating Expenses Caption [Text] rr_OperatingExpensesCaption Annual Fund Operating Expenses (expenses that you pay each year as a percentage of the value of your investment)
Fee Waiver or Reimbursement over Assets, Date of Termination rr_FeeWaiverOrReimbursementOverAssetsDateOfTermination February 1, 2023
Portfolio Turnover [Heading] rr_PortfolioTurnoverHeading Portfolio Turnover.
Portfolio Turnover [Text Block] rr_PortfolioTurnoverTextBlock

The Fund pays transaction costs, such as commissions, when it buys and sells securities (or “turns over”) its portfolio. A higher portfolio turnover rate may indicate higher transaction costs and may result in higher taxes when Fund shares are held in a taxable account. These costs, which are not reflected in Annual Fund Operating Expenses or in the Example, affect the Fund’s performance. During the most recent fiscal year, the Fund’s portfolio turnover rate was 161.43% of the average value of its portfolio.
Portfolio Turnover, Rate rr_PortfolioTurnoverRate 161.43%
Expense Breakpoint Discounts [Text] rr_ExpenseBreakpointDiscounts You may qualify for discounts from the sales charges applicable to Class A shares if you or other qualifying account holders invest, or agree to invest in the future, at least $50,000 in the Thornburg Funds.
Expense Breakpoint, Minimum Investment Required [Amount] rr_ExpenseBreakpointMinimumInvestmentRequiredAmount $ 50,000
Expense Example [Heading] rr_ExpenseExampleHeading Example.
Expense Example Narrative [Text Block] rr_ExpenseExampleNarrativeTextBlock

This Example is intended to help you compare the cost of investing in the Fund with the cost of investing in other mutual funds.

The Example assumes that you invest $10,000 in the Fund for the time periods indicated and then redeem all of your shares at the end of those periods. The Example also assumes that your investment has a 5% return each year, dividends and distributions are reinvested, and that the Fund’s operating expenses remain the same. Although your actual costs may be higher or lower, based on these assumptions (and giving effect to fee waivers and expense reimbursements in the first year), your costs would be:
Expense Example, No Redemption Narrative [Text Block] rr_ExpenseExampleNoRedemptionNarrativeTextBlock

You would pay the following expenses if you did not redeem your Class C shares:
Strategy [Heading] rr_StrategyHeading Principal Investment Strategies
Strategy Narrative [Text Block] rr_StrategyNarrativeTextBlock

Under normal conditions, the Fund invests at least 80% of its net assets in small- and mid-capitalization companies. The Fund currently defines small- and mid-capitalization companies to be those within the market capitalization range comprised by the Russell 2500 Growth Index – Total Return. As of November 30, 2021, the market capitalization range of the Russell 2500 Growth Index – Total Return was approximately $5 million to $33 billion. The market capitalization range of the Russell 2500 Growth Index – Total Return changes over time and, as a result, the capitalization range of companies in which the Fund invests will also change. The Fund may change the definition of what constitutes “small- and mid-capitalization companies” without advance notice to shareholders.

The Fund expects to invest primarily in domestic common stocks. However, the Fund may own foreign common stocks which, in the opinion of the Fund’s investment advisor, Thornburg Investment Management, Inc. (“Thornburg”), offer prospects for meeting the Fund’s investment goal.

The Fund seeks to invest in a diversified portfolio of companies the Fund categorizes as consistent growers, disruptors, and emerging franchises, as described in more detail below. The relative proportions of securities invested in each of those categories will vary over time.

Thornburg primarily takes a bottom-up, fundamental view in determining the attractiveness of individual securities and in making investment decisions. Among the specific factors considered by Thornburg in identifying securities for inclusion in the Fund are:

•earnings growth potential

•durable business model

•industry growth potential

•innovation driving the potential to disrupt entrenched competitors

•intrinsic value appreciation potential

•potential size of addressable market

•management strength

•leverage

•return on invested capital

•valuation metrics, including: price/earnings (“PE”) ratio; enterprise value/revenue ratio; PE/growth rate ratio, enterprise value/EBITDA (earnings before interest, taxes, depreciation and amortization) ratio; and free cash flow yield.

The Fund categorizes its equity investments in the following three categories:

Consistent Growers: Companies in this category generally exhibit steady earnings or revenue growth, or both. These companies may have subscription or other recurring revenue profiles. Given their business models, these companies may outperform in weak markets.

Disruptors: Companies which are at the early stages of growth; which usually possess highly innovative or differentiated products and services, but which may require substantial additional time or investment to capitalize on market opportunities and achieve profitability.

Emerging Franchises: Companies with the potential to grow at an above average rate because of a product or service that is establishing a new market and/or taking share from existing participants.

Inclusion of any investment in any of the three described categories represents the opinion of the advisor concerning the characteristics and prospects of the investment. There is no assurance that any company selected for investment will, once categorized in one of the three described investment categories, continue to have the positive characteristics or fulfill the expectations that the advisor had for the company when it was selected for investment, and any such company may not grow or may decline in earnings and size.

The Fund selects foreign securities issued by companies domiciled in countries whose currencies are freely convertible into U.S. dollars, or in companies in other countries whose business is conducted primarily in U.S. dollars.

The Fund may sell an investment if Thornburg has identified a better investment opportunity, in response to changes in the conditions or business of the investment’s issuer or changes in overall market conditions, if Thornburg has a target price for the investment and that target price has been achieved, or if, in Thornburg’s opinion, the investment no longer serves to achieve the Fund’s investment goals.

The Fund’s policy of investing at least 80% of its assets in small- and mid-capitalization companies may be changed by the Fund’s Trustees without a shareholder vote upon 60 days’ notice to shareholders.
Risk [Heading] rr_RiskHeading Principal Investment Risks
Risk Narrative [Text Block] rr_RiskNarrativeTextBlock

An investment in the Fund is not a deposit in any bank and is not insured or guaranteed by the Federal Deposit Insurance Corporation or any other governmental agency. Accordingly, the loss of money is a risk of investing in the Fund. The value of the Fund’s shares varies from day to day and over time, and when you sell your shares they may be worth less than what you paid for them. The following is a summary of the principal risks of investing in the Fund.

Management Risk – The Fund is an actively managed portfolio, and the value of the Fund may be reduced if Thornburg pursues unsuccessful investments or fails to correctly identify risks affecting the broad economy or specific issuers in which the Fund invests.

Market and Economic Risk – The value of the Fund’s investments may decline and its share value may be reduced due to changes in general economic and market conditions. The value of a security may change in response to developments affecting entire economies, markets or industries, including changes in interest rates, political and legal developments, and general market volatility.

Equity Risk – The value of the Fund’s equity investments may fluctuate significantly over time in response to factors affecting individual issuers, particular industries, or the market as a whole. Additionally, common stock ranks below preferred stock and debt securities in claims for dividends and for assets of a company in a liquidation or bankruptcy.

Risks Affecting Specific Issuers – The value of a security may decline in response to developments affecting the specific issuer of the security, even if the overall industry or economy is unaffected. These developments may include a variety of factors, including but not limited to management issues or other corporate disruption, a decline in revenues or profitability, an increase in costs, or an adverse effect on the issuer’s competitive position.

Small and Mid-Cap Company Risk – Investments in small-capitalization companies and mid-capitalization companies may involve additional risks, which may be relatively higher with smaller companies. These additional risks may result from limited product lines, earlier stages of development and lack of well-established businesses, more limited access to markets and financial resources, greater vulnerability to competition and market risks and fluctuations, lack of management depth, increased volatility in share price, and possible difficulties in valuing or selling these investments. Relative to the stocks of large capitalization companies, the stocks of small- and mid-capitalization companies may be thinly traded and sales may result in higher transaction costs. Also, small- and mid-capitalization companies may perform poorly during times of economic stress.

Foreign Investment Risk – Investments in securities of foreign issuers may involve risks including adverse fluctuations in currency exchange rates, political instability, confiscations, taxes or restrictions on currency exchange, difficulty in selling foreign investments, and reduced legal protection.

Liquidity Risk – Due to a lack of demand in the marketplace or other factors, the Fund may not be able to sell some or all of its investments promptly, or may only be able to sell investments at less than desired prices.

Additional information about Fund investments, investment strategies, and risks of investing in the Fund appears below beginning on page 118.

Cybersecurity and Operational Risk – Operational failures, cyber-attacks or other disruptions that affect the Fund’s service providers, the Fund’s counterparties, other market participants or the issuers of securities held by the Fund may adversely affect the Fund and its shareholders, including by causing losses for the Fund or impairing Fund operations.
Risk Lose Money [Text] rr_RiskLoseMoney Accordingly, the loss of money is a risk of investing in the Fund.
RIsk Not Insured [Text] rr_RiskNotInsured An investment in the Fund is not a deposit in any bank and is not insured or guaranteed by the Federal Deposit Insurance Corporation or any other governmental agency.
Bar Chart and Performance Table [Heading] rr_BarChartAndPerformanceTableHeading Past Performance of the Fund
Performance Narrative [Text Block] rr_PerformanceNarrativeTextBlock

The following information provides some indication of the risks of investing in the Small/Mid Cap Growth Fund by showing how the Fund’s investment results vary from year to year. The bar chart shows how the annual total returns for Class A shares have been different in each full year shown. The average annual total return figures compare Class A, Class C and Class I share performance to the Russell 2500 Growth Index—Total Return, a broad measure of market performance. Past performance (before and after taxes) is not necessarily an indication of how the Fund will perform in the future. The performance information shown is as of the calendar year ended December 31, 2021. Updated performance information may be obtained on the Thornburg website at Thornburg.com or by calling 1-800-847-0200.

Performance Information Illustrates Variability of Returns [Text] rr_PerformanceInformationIllustratesVariabilityOfReturns The following information provides some indication of the risks of investing in the Small/Mid Cap Growth Fund by showing how the Fund’s investment results vary from year to year.
Performance Availability Phone [Text] rr_PerformanceAvailabilityPhone 1-800-847-0200
Performance Availability Website Address [Text] rr_PerformanceAvailabilityWebSiteAddress Thornburg.com
Performance Past Does Not Indicate Future [Text] rr_PerformancePastDoesNotIndicateFuture Past performance (before and after taxes) is not necessarily an indication of how the Fund will perform in the future.
Bar Chart [Heading] rr_BarChartHeading Annual Total Returns – Class A Shares
Bar Chart Does Not Reflect Sales Loads [Text] rr_BarChartDoesNotReflectSalesLoads The sales charge for Class A shares is not reflected in the returns shown in the bar chart, and the returns would be less if the charge was taken into account.
Bar Chart Closing [Text Block] rr_BarChartClosingTextBlock

Total
Returns

Quarter
ended

Highest Quarterly Results

30.93%

6/30/2020

Lowest Quarterly Results

(18.72)%

9/30/2011

The sales charge for Class A shares is not reflected in the returns shown in the bar chart, and the returns would be less if the charge was taken into account.
Performance Table Heading rr_PerformanceTableHeading Average Annual Total Returns (periods ended 12-31-21)
Performance Table Uses Highest Federal Rate rr_PerformanceTableUsesHighestFederalRate fter-tax returns are calculated using the highest historical individual federal marginal income tax rates, and do not reflect state or local income taxes.
Performance Table Not Relevant to Tax Deferred rr_PerformanceTableNotRelevantToTaxDeferred Actual after-tax returns depend on an investor’s own tax situation and may differ from the returns shown, and after-tax returns shown are not relevant to investors who hold their Fund shares through tax-deferred arrangements, such as 401(k) plans or individual retirement accounts.
Performance Table One Class of after Tax Shown [Text] rr_PerformanceTableOneClassOfAfterTaxShown The after-tax returns shown relate only to Class A shares, and after-tax returns for other share classes will vary.
Performance Table Closing [Text Block] rr_PerformanceTableClosingTextBlock

After-tax returns are calculated using the highest historical individual federal marginal income tax rates, and do not reflect state or local income taxes. Actual after-tax returns depend on an investor’s own tax situation and may differ from the returns shown, and after-tax returns shown are not relevant to investors who hold their Fund shares through tax-deferred arrangements, such as 401(k) plans or individual retirement accounts. The after-tax returns shown relate only to Class A shares, and after-tax returns for other share classes will vary.
Retail | Thornburg Small/Mid Cap Growth Fund | Thornburg Small/Mid Cap Growth Fund - Class A  
Prospectus [Line Items] rr_ProspectusLineItems  
Trading Symbol dei_TradingSymbol THCGX
Maximum Sales Charge Imposed on Purchases (as a percentage of Offering Price) rr_MaximumSalesChargeImposedOnPurchasesOverOfferingPrice 4.50%
Maximum Deferred Sales Charge (as a percentage) rr_MaximumDeferredSalesChargeOverOther none [21]
Management Fees (as a percentage of Assets) rr_ManagementFeesOverAssets 0.86%
Distribution and Service (12b-1) Fees rr_DistributionAndService12b1FeesOverAssets 0.25%
Other Expenses (as a percentage of Assets): rr_OtherExpensesOverAssets 0.20%
Expenses (as a percentage of Assets) rr_ExpensesOverAssets 1.31%
Fee Waiver or Reimbursement rr_FeeWaiverOrReimbursementOverAssets
Net Expenses (as a percentage of Assets) rr_NetExpensesOverAssets 1.31%
Expense Example, with Redemption, 1 Year rr_ExpenseExampleYear01 $ 577
Expense Example, with Redemption, 3 Years rr_ExpenseExampleYear03 847
Expense Example, with Redemption, 5 Years rr_ExpenseExampleYear05 1,136
Expense Example, with Redemption, 10 Years rr_ExpenseExampleYear10 $ 1,958
Annual Return 2012 rr_AnnualReturn2012 21.42%
Annual Return 2013 rr_AnnualReturn2013 42.59%
Annual Return 2014 rr_AnnualReturn2014 0.07%
Annual Return 2015 rr_AnnualReturn2015 2.78%
Annual Return 2016 rr_AnnualReturn2016 (2.35%)
Annual Return 2017 rr_AnnualReturn2017 23.91%
Annual Return 2018 rr_AnnualReturn2018 (2.56%)
Annual Return 2019 rr_AnnualReturn2019 28.91%
Annual Return 2020 rr_AnnualReturn2020 41.65%
Annual Return 2021 rr_AnnualReturn2021 (4.32%)
Highest Quarterly Return, Label rr_HighestQuarterlyReturnLabel Highest Quarterly Results
Highest Quarterly Return, Date rr_BarChartHighestQuarterlyReturnDate Jun. 30, 2020
Highest Quarterly Return rr_BarChartHighestQuarterlyReturn 30.93%
Lowest Quarterly Return, Label rr_LowestQuarterlyReturnLabel Lowest Quarterly Results
Lowest Quarterly Return, Date rr_BarChartLowestQuarterlyReturnDate Sep. 30, 2011
Lowest Quarterly Return rr_BarChartLowestQuarterlyReturn (18.72%)
1 Year rr_AverageAnnualReturnYear01 (8.62%)
5 Years rr_AverageAnnualReturnYear05 15.04%
10 Years rr_AverageAnnualReturnYear10 13.36%
Retail | Thornburg Small/Mid Cap Growth Fund | Thornburg Small/Mid Cap Growth Fund - Class A | After Taxes on Distributions  
Prospectus [Line Items] rr_ProspectusLineItems  
1 Year rr_AverageAnnualReturnYear01 (16.00%)
5 Years rr_AverageAnnualReturnYear05 12.25%
10 Years rr_AverageAnnualReturnYear10 11.98%
Retail | Thornburg Small/Mid Cap Growth Fund | Thornburg Small/Mid Cap Growth Fund - Class A | After Taxes on Distributions and Sales  
Prospectus [Line Items] rr_ProspectusLineItems  
1 Year rr_AverageAnnualReturnYear01 0.73%
5 Years rr_AverageAnnualReturnYear05 12.05%
10 Years rr_AverageAnnualReturnYear10 11.22%
Retail | Thornburg Small/Mid Cap Growth Fund | Thornburg Small/Mid Cap Growth Fund - Class A | Russell 2500 Growth Index-Total Return (reflects no deduction for fees, expenses, or taxes)  
Prospectus [Line Items] rr_ProspectusLineItems  
1 Year rr_AverageAnnualReturnYear01 5.04%
5 Years rr_AverageAnnualReturnYear05 17.65%
10 Years rr_AverageAnnualReturnYear10 15.75%
Retail | Thornburg Small/Mid Cap Growth Fund | Thornburg Small/Mid Cap Growth Fund - Class C  
Prospectus [Line Items] rr_ProspectusLineItems  
Trading Symbol dei_TradingSymbol TCGCX
Maximum Sales Charge Imposed on Purchases (as a percentage of Offering Price) rr_MaximumSalesChargeImposedOnPurchasesOverOfferingPrice none
Maximum Deferred Sales Charge (as a percentage) rr_MaximumDeferredSalesChargeOverOther 1.00% [22]
Management Fees (as a percentage of Assets) rr_ManagementFeesOverAssets 0.86%
Distribution and Service (12b-1) Fees rr_DistributionAndService12b1FeesOverAssets 1.00%
Other Expenses (as a percentage of Assets): rr_OtherExpensesOverAssets 0.23%
Expenses (as a percentage of Assets) rr_ExpensesOverAssets 2.09%
Fee Waiver or Reimbursement rr_FeeWaiverOrReimbursementOverAssets
Net Expenses (as a percentage of Assets) rr_NetExpensesOverAssets 2.09%
Expense Example, with Redemption, 1 Year rr_ExpenseExampleYear01 $ 312
Expense Example, with Redemption, 3 Years rr_ExpenseExampleYear03 655
Expense Example, with Redemption, 5 Years rr_ExpenseExampleYear05 1,124
Expense Example, with Redemption, 10 Years rr_ExpenseExampleYear10 2,421
Expense Example, No Redemption, 1 Year rr_ExpenseExampleNoRedemptionYear01 212
Expense Example, No Redemption, 3 Years rr_ExpenseExampleNoRedemptionYear03 655
Expense Example, No Redemption, 5 Years rr_ExpenseExampleNoRedemptionYear05 1,124
Expense Example, No Redemption, 10 Years rr_ExpenseExampleNoRedemptionYear10 $ 2,421
1 Year rr_AverageAnnualReturnYear01 (5.62%)
5 Years rr_AverageAnnualReturnYear05 15.18%
10 Years rr_AverageAnnualReturnYear10 13.01%
Retail | Thornburg Small/Mid Cap Growth Fund | Thornburg Small/Mid Cap Growth Fund - Class C | Russell 2500 Growth Index-Total Return (reflects no deduction for fees, expenses, or taxes)  
Prospectus [Line Items] rr_ProspectusLineItems  
1 Year rr_AverageAnnualReturnYear01 5.04%
5 Years rr_AverageAnnualReturnYear05 17.65%
10 Years rr_AverageAnnualReturnYear10 15.75%
Retail | Thornburg Small/Mid Cap Growth Fund | Thornburg Small/Mid Cap Growth Fund - Class I  
Prospectus [Line Items] rr_ProspectusLineItems  
Trading Symbol dei_TradingSymbol THIGX
Maximum Sales Charge Imposed on Purchases (as a percentage of Offering Price) rr_MaximumSalesChargeImposedOnPurchasesOverOfferingPrice none
Maximum Deferred Sales Charge (as a percentage) rr_MaximumDeferredSalesChargeOverOther none
Management Fees (as a percentage of Assets) rr_ManagementFeesOverAssets 0.86%
Distribution and Service (12b-1) Fees rr_DistributionAndService12b1FeesOverAssets none
Other Expenses (as a percentage of Assets): rr_OtherExpensesOverAssets 0.18%
Expenses (as a percentage of Assets) rr_ExpensesOverAssets 1.04%
Fee Waiver or Reimbursement rr_FeeWaiverOrReimbursementOverAssets (0.09%) [23]
Net Expenses (as a percentage of Assets) rr_NetExpensesOverAssets 0.95%
Expense Example, with Redemption, 1 Year rr_ExpenseExampleYear01 $ 97
Expense Example, with Redemption, 3 Years rr_ExpenseExampleYear03 322
Expense Example, with Redemption, 5 Years rr_ExpenseExampleYear05 565
Expense Example, with Redemption, 10 Years rr_ExpenseExampleYear10 $ 1,263
1 Year rr_AverageAnnualReturnYear01 (3.99%)
5 Years rr_AverageAnnualReturnYear05 16.51%
10 Years rr_AverageAnnualReturnYear10 14.32%
Retail | Thornburg Small/Mid Cap Growth Fund | Thornburg Small/Mid Cap Growth Fund - Class I | Russell 2500 Growth Index-Total Return (reflects no deduction for fees, expenses, or taxes)  
Prospectus [Line Items] rr_ProspectusLineItems  
1 Year rr_AverageAnnualReturnYear01 5.04%
5 Years rr_AverageAnnualReturnYear05 17.65%
10 Years rr_AverageAnnualReturnYear10 15.75%
Retail | Thornburg Investment Income Builder Fund  
Prospectus [Line Items] rr_ProspectusLineItems  
Risk/Return [Heading] rr_RiskReturnHeading Income Builder Fund
Objective [Heading] rr_ObjectiveHeading Investment Goal
Objective, Primary [Text Block] rr_ObjectivePrimaryTextBlock

The Fund’s primary investment goal is to provide a level of current income which exceeds the average yield on U.S. stocks generally, and which will generally grow, subject to periodic fluctuations, over the years on a per share basis.
Objective, Secondary [Text Block] rr_ObjectiveSecondaryTextBlock

The Fund’s secondary investment goal is long-term capital appreciation.
Expense [Heading] rr_ExpenseHeading Fees and Expenses of the Fund
Expense Narrative [Text Block] rr_ExpenseNarrativeTextBlock

This table describes the fees and expenses that you may pay if you buy and hold shares of the Fund. You may qualify for discounts from the sales charges applicable to Class A shares if you or other qualifying account holders invest, or agree to invest in the future, at least $50,000 in the Thornburg Funds. More information about this and other discounts and sales charge waivers is available from your financial intermediary, in the Prospectus under the captions “Class A Sales Charge Waivers,” beginning on page 146, and “Appendix A – Sales Charge Waivers Offered by Financial Intermediaries,” beginning on page 200, and in the Statement of Additional Information under the caption “Additional Information Respecting Purchase and Redemption of Shares,” beginning on page 108.
Shareholder Fees Caption [Text] rr_ShareholderFeesCaption Shareholder Fees (fees paid directly from your investment)
Operating Expenses Caption [Text] rr_OperatingExpensesCaption Annual Fund Operating Expenses (expenses that you pay each year as a percentage of the value of your investment)
Portfolio Turnover [Heading] rr_PortfolioTurnoverHeading Portfolio Turnover.
Portfolio Turnover [Text Block] rr_PortfolioTurnoverTextBlock

The Fund pays transaction costs, such as commissions, when it buys and sells securities (or “turns over”) its portfolio. A higher portfolio turnover rate may indicate higher transaction costs and may result in higher taxes when Fund shares are held in a taxable account. These costs, which are not reflected in Annual Fund Operating Expenses or in the Example, affect the Fund’s performance. During the most recent fiscal year, the Fund’s portfolio turnover rate was 18.99% of the average value of its portfolio.
Portfolio Turnover, Rate rr_PortfolioTurnoverRate 18.99%
Expense Breakpoint Discounts [Text] rr_ExpenseBreakpointDiscounts You may qualify for discounts from the sales charges applicable to Class A shares if you or other qualifying account holders invest, or agree to invest in the future, at least $50,000 in the Thornburg Funds.
Expense Breakpoint, Minimum Investment Required [Amount] rr_ExpenseBreakpointMinimumInvestmentRequiredAmount $ 50,000
Expense Example [Heading] rr_ExpenseExampleHeading Example.
Expense Example Narrative [Text Block] rr_ExpenseExampleNarrativeTextBlock

This Example is intended to help you compare the cost of investing in the Fund with the cost of investing in other mutual funds.

The Example assumes that you invest $10,000 in the Fund for the time periods indicated and then redeem all of your shares at the end of those periods. The Example also assumes that your investment has a 5% return each year, dividends and distributions are reinvested, and that the Fund’s operating expenses remain the same. Although your actual costs may be higher or lower, based on these assumptions, your costs would be:
Expense Example, No Redemption Narrative [Text Block] rr_ExpenseExampleNoRedemptionNarrativeTextBlock

You would pay the following expenses if you did not redeem your Class C shares:
Strategy [Heading] rr_StrategyHeading Principal Investment Strategies
Strategy Narrative [Text Block] rr_StrategyNarrativeTextBlock

The Fund pursues its investment goals by investing in a broad range of income producing securities, primarily including stocks and bonds, as described below. The Fund will under normal conditions invest at least 80% of its assets in income-producing securities, and at least 50% of its assets in common stocks.

The Fund may invest in any stock or other equity security which the investment advisor believes may assist the Fund in pursuing its investment goals (including smaller companies with market capitalization of less than $500 million and companies in developing countries), including preferred stock and publicly traded real estate investment trusts. The Fund expects that equity investments in the Fund’s portfolio normally will be weighted in favor of companies which pay dividends or other current income.

The Fund may invest in debt obligations of any kind, including corporate bonds and other obligations, mortgage- and other asset-backed securities and government obligations. The Fund may purchase debt obligations of any maturity and of any credit quality, including “high yield” or “junk” bonds. There is no minimum credit quality or rating of debt obligation the Fund may purchase. The Fund also may invest in debt obligations which have a combination of equity and debt characteristics, such as convertible bonds.

The Fund may invest a significant portion of its assets in securities of issuers domiciled in or economically tied to countries outside the United States, including developing countries.

The Fund’s investments are determined by individual issuer and industry analysis. Investment decisions are based on domestic and international economic developments, outlooks for securities markets, interest rates and inflation, the supply and demand for debt and equity securities, and analysis of specific issuers. The Fund ordinarily acquires and holds debt obligations for investment rather than for realization of gains by short-term trading on market fluctuations. However, the Fund may dispose of any such security prior to its scheduled maturity to enhance income or reduce loss, to change the portfolio’s average maturity, or otherwise to respond to market conditions.

The Fund may sell an investment if Thornburg has identified a better investment opportunity, in response to changes in the conditions or business of the investment’s issuer or changes in overall market conditions, if Thornburg has a target price for the investment and that target price has been achieved, or if, in Thornburg’s opinion, the investment no longer serves to achieve the Fund’s investment goals.
Risk [Heading] rr_RiskHeading Principal Investment Risks
Risk Narrative [Text Block] rr_RiskNarrativeTextBlock

An investment in the Fund is not a deposit in any bank and is not insured or guaranteed by the Federal Deposit Insurance Corporation or any other government agency. Accordingly, the loss of money is a risk of investing in the Fund. The value of the Fund’s shares varies from day to day and over time, and when you sell your shares they may be worth less than what you paid for them. The following is a summary of the principal risks of investing in the Fund.

Management Risk – The Fund is an actively managed portfolio, and the value of the Fund may be reduced if Thornburg pursues unsuccessful investments or fails to correctly identify risks affecting the broad economy or specific issuers in which the Fund invests.

Market and Economic Risk – The value of the Fund’s investments may decline and its share value may be reduced due to changes in general economic and market conditions. The value of a security may change in response to developments affecting entire economies, markets or industries, including changes in interest rates, political and legal developments, and general market volatility.

Equity Risk – The value of the Fund’s equity investments may fluctuate significantly over time in response to factors affecting individual issuers, particular industries, or the market as a whole. Additionally, common stock ranks below preferred stock and debt securities in claims for dividends and for assets of a company in a liquidation or bankruptcy.

Risks Affecting Specific Issuers – The value of an equity security or debt obligation may decline in response to developments affecting the specific issuer of the security or obligation, even if the overall industry or economy is unaffected. These developments may include a variety of factors, including but not limited to management issues or other corporate disruption, a decline in revenues or profitability, an increase in costs, or an adverse effect on the issuer’s competitive position.

Small and Mid-Cap Company Risk – Investments in small-capitalization companies and mid-capitalization companies may involve additional risks, which may be relatively higher with smaller companies. These additional risks may result from limited product lines, more limited access to markets and financial resources, greater vulnerability to competition and changes in markets, lack of management depth, increased volatility in share price, and possible difficulties in valuing or selling these investments.

Credit Risk – If debt obligations held by the Fund are downgraded by ratings agencies or go into default, or if management action, legislation or other government action reduces the ability of issuers to pay principal and interest when due, the value of those obligations may decline and the Fund’s share value and the dividends paid by the Fund may be reduced. Because the ability of an issuer of a lower-rated or unrated obligation to pay principal and interest when due is typically less certain than for an issuer of a higher-rated obligation, lower-rated and unrated obligations are generally more vulnerable than higher-rated obligations to default, to ratings downgrades, and to liquidity risk. The inability of an issuer to pay principal and interest on its debt obligations when due, or the downgrading of an issuer’s debt obligations by ratings agencies, may adversely affect the market’s perceptions of the issuer’s financial strength and may therefore result in declines in the issuer’s stock price.

High Yield Risk – Debt obligations that are rated below investment grade and unrated obligations of similar credit quality (commonly referred to as “junk” or “high yield” bonds) may have a substantial risk of loss. These obligations are generally considered to be speculative with respect to the issuer’s ability to pay interest and principal when due. These obligations may be subject to greater price volatility than investment grade obligations, and their prices may decline significantly in periods of general economic difficulty or in response to adverse publicity, changes in investor perceptions or other factors. These obligations may also be subject to greater liquidity risk.

Interest Rate Risk – When interest rates increase, the value of the Fund’s investments in debt obligations may decline and the Fund’s share value may be reduced. This effect is typically more pronounced for intermediate and longer-term obligations. This effect is also typically more pronounced for mortgage- and other asset-backed securities, the value of which may fluctuate more significantly in response to interest rate changes. When interest rates decrease, the Fund’s dividends may decline.

Prepayment and Extension Risk – When market interest rates decline, certain debt obligations held by the Fund may be repaid more quickly than anticipated, requiring the Fund to reinvest the proceeds of those repayments in obligations which bear a lower interest rate. Conversely, when market interest rates increase, certain debt obligations held by the Fund may be repaid more slowly than anticipated, causing assets of the Fund to remain invested in relatively lower yielding obligations. These risks may be more pronounced for the Fund’s investments in mortgage-backed and asset-backed securities.

Foreign Investment Risk – Investments in securities of foreign issuers may involve risks including adverse fluctuations in currency exchange rates, political instability, confiscations, taxes or restrictions on currency exchange, difficulty in selling foreign investments, and reduced legal protection. In addition, some foreign government debt obligations may be subject to default, delays in payment, adverse legislation or government action, or could be downgraded by ratings agencies.

Developing Country Risk – The risks which may affect investments in foreign issuers (see “Foreign Investment Risk,” above) may be more pronounced for investments in developing countries because the economies of those countries are usually less diversified, communications, transportation and economic infrastructures are less developed, and developing countries ordinarily have less established legal, political, business and social frameworks. At times the prices of equity securities or debt obligations of a developing country issuer may be extremely volatile. An issuer domiciled in a developed country may be similarly affected by these developing country risks to the extent that the issuer conducts its business in developing countries.

Foreign Currency Risk – Fluctuations in currency exchange rates can adversely affect the value of the Fund’s foreign investments. Such fluctuations may occur for a number of reasons, including market and economic conditions, or a government’s decision to devalue its currency or impose currency controls.

Risks Affecting Specific Countries or Regions – If a significant portion of the Fund’s assets is invested in issuers that are economically exposed to one country or region, the Fund’s share value may be more susceptible to the conditions and developments in that country or region, and potentially more volatile than the share value of a more geographically diversified fund. A specific country or region could also be adversely affected by conditions or developments arising in other countries. For example, the U.S. government could take actions to prohibit or restrict individuals or companies within the U.S. from purchasing or holding the shares of issuers in another country, which may limit the Fund’s ability to invest in that country or cause the Fund to have to sell investments in that country at less than desired prices. The nature and degree of the risks affecting a given country or region, and the extent of the Fund’s exposure to any such country or region, is expected to vary over time.

Liquidity Risk – Due to a lack of demand in the marketplace or other factors, the Fund may not be able to sell some or all of its investments promptly, or may only be able to sell investments at less than desired prices.

Real Estate Risk – The Fund’s investments in publicly traded real estate investment trusts (“REITs”) are subject to risks affecting real estate investments generally (including market conditions, competition, property obsolescence, changes in interest rates and casualty to real estate), as well as risks specifically affecting REITs (the quality and skill of REIT management and the internal expenses of the REIT).

Cybersecurity and Operational Risk – Operational failures, cyber-attacks or other disruptions that affect the Fund’s service providers, the Fund’s counterparties, other market participants or the issuers of securities held by the Fund may adversely affect the Fund and its shareholders, including by causing losses for the Fund or impairing Fund operations.

Additional information about Fund investments, investment strategies and risks of investing in the Fund appears beginning on page 118 of the Prospectus.
Risk Lose Money [Text] rr_RiskLoseMoney Accordingly, the loss of money is a risk of investing in the Fund.
RIsk Not Insured [Text] rr_RiskNotInsured An investment in the Fund is not a deposit in any bank and is not insured or guaranteed by the Federal Deposit Insurance Corporation or any other government agency.
Bar Chart and Performance Table [Heading] rr_BarChartAndPerformanceTableHeading Past Performance of the Fund
Performance Narrative [Text Block] rr_PerformanceNarrativeTextBlock

The following information provides some indication of the risks of investing in Income Builder Fund by showing how the Fund’s investment results vary from year to year. The bar chart shows how the annual total returns for Class A shares have been different in each full year shown. The average annual total return figures compare Class A, Class C and Class I share performance to a Blended Benchmark comprised of 25% Bloomberg Barclays US Aggregate Bond Total Return Value USD, which represents a broad measure of bond market performance, and 75% MSCI World Net Total Return USD Index, which represents a broad measure of equity market performance in developed markets. Past performance (before and after taxes) is not necessarily an indication of how the Fund will perform in the future. The performance information shown is as of the calendar year ended December 31, 2021. Updated performance information may be obtained on the Thornburg website at Thornburg.com or by calling 1-800-847-0200.
Performance Information Illustrates Variability of Returns [Text] rr_PerformanceInformationIllustratesVariabilityOfReturns The following information provides some indication of the risks of investing in Income Builder Fund by showing how the Fund’s investment results vary from year to year.
Performance Availability Phone [Text] rr_PerformanceAvailabilityPhone 1-800-847-0200
Performance Availability Website Address [Text] rr_PerformanceAvailabilityWebSiteAddress Thornburg.com
Performance Past Does Not Indicate Future [Text] rr_PerformancePastDoesNotIndicateFuture Past performance (before and after taxes) is not necessarily an indication of how the Fund will perform in the future.
Bar Chart [Heading] rr_BarChartHeading Annual Total Returns – Class A Shares
Bar Chart Does Not Reflect Sales Loads [Text] rr_BarChartDoesNotReflectSalesLoads The sales charge for Class A shares is not reflected in the returns shown on the bar chart, and the returns would be less if the charge was taken into account.
Bar Chart Closing [Text Block] rr_BarChartClosingTextBlock

Total
Returns

Quarter
ended

Highest Quarterly Results

15.96%

12/31/2020

Lowest Quarterly Results

(25.98)%

3/31/2020

The sales charge for Class A shares is not reflected in the returns shown on the bar chart, and the returns would be less if the charge was taken into account.
Performance Table Heading rr_PerformanceTableHeading Average Annual Total Returns (periods ended 12-31-21)
Performance Table Uses Highest Federal Rate rr_PerformanceTableUsesHighestFederalRate After-tax returns are calculated using the highest historical individual federal marginal income tax rates, and do not reflect state or local income taxes.
Performance Table Not Relevant to Tax Deferred rr_PerformanceTableNotRelevantToTaxDeferred Actual after-tax returns depend on an investor’s own tax situation and may differ from the returns shown, and after-tax returns shown are not relevant to investors who hold their Fund shares through tax-deferred arrangements, such as 401(k) plans or individual retirement accounts.
Performance Table One Class of after Tax Shown [Text] rr_PerformanceTableOneClassOfAfterTaxShown The after-tax returns shown relate only to Class A shares, and after-tax returns for other share classes will vary.
Performance Table Closing [Text Block] rr_PerformanceTableClosingTextBlock

After-tax returns are calculated using the highest historical individual federal marginal income tax rates, and do not reflect state or local income taxes. Actual after-tax returns depend on an investor’s own tax situation and may differ from the returns shown, and after-tax returns shown are not relevant to investors who hold their Fund shares through tax-deferred arrangements, such as 401(k) plans or individual retirement accounts. The after-tax returns shown relate only to Class A shares, and after-tax returns for other share classes will vary.
Retail | Thornburg Investment Income Builder Fund | Thornburg Investment Income Builder Fund - Class A  
Prospectus [Line Items] rr_ProspectusLineItems  
Trading Symbol dei_TradingSymbol TIBAX
Maximum Sales Charge Imposed on Purchases (as a percentage of Offering Price) rr_MaximumSalesChargeImposedOnPurchasesOverOfferingPrice 4.50%
Maximum Deferred Sales Charge (as a percentage) rr_MaximumDeferredSalesChargeOverOther none [24]
Management Fees (as a percentage of Assets) rr_ManagementFeesOverAssets 0.70%
Distribution and Service (12b-1) Fees rr_DistributionAndService12b1FeesOverAssets 0.25%
Other Expenses (as a percentage of Assets): rr_OtherExpensesOverAssets 0.18% [25]
Acquired Fund Fees and Expenses rr_AcquiredFundFeesAndExpensesOverAssets 0.05%
Expenses (as a percentage of Assets) rr_ExpensesOverAssets 1.18% [26]
Expense Example, with Redemption, 1 Year rr_ExpenseExampleYear01 $ 565
Expense Example, with Redemption, 3 Years rr_ExpenseExampleYear03 808
Expense Example, with Redemption, 5 Years rr_ExpenseExampleYear05 1,070
Expense Example, with Redemption, 10 Years rr_ExpenseExampleYear10 $ 1,817
Annual Return 2012 rr_AnnualReturn2012 11.36%
Annual Return 2013 rr_AnnualReturn2013 16.50%
Annual Return 2014 rr_AnnualReturn2014 4.54%
Annual Return 2015 rr_AnnualReturn2015 (5.37%)
Annual Return 2016 rr_AnnualReturn2016 9.50%
Annual Return 2017 rr_AnnualReturn2017 14.78%
Annual Return 2018 rr_AnnualReturn2018 (4.62%)
Annual Return 2019 rr_AnnualReturn2019 17.66%
Annual Return 2020 rr_AnnualReturn2020 (0.65%)
Annual Return 2021 rr_AnnualReturn2021 20.02%
Highest Quarterly Return, Label rr_HighestQuarterlyReturnLabel Highest Quarterly Results
Highest Quarterly Return, Date rr_BarChartHighestQuarterlyReturnDate Dec. 31, 2020
Highest Quarterly Return rr_BarChartHighestQuarterlyReturn 15.96%
Lowest Quarterly Return, Label rr_LowestQuarterlyReturnLabel Lowest Quarterly Results
Lowest Quarterly Return, Date rr_BarChartLowestQuarterlyReturnDate Mar. 31, 2020
Lowest Quarterly Return rr_BarChartLowestQuarterlyReturn (25.98%)
1 Year rr_AverageAnnualReturnYear01 14.62%
5 Years rr_AverageAnnualReturnYear05 7.96%
10 Years rr_AverageAnnualReturnYear10 7.50%
Retail | Thornburg Investment Income Builder Fund | Thornburg Investment Income Builder Fund - Class A | After Taxes on Distributions  
Prospectus [Line Items] rr_ProspectusLineItems  
1 Year rr_AverageAnnualReturnYear01 12.21%
5 Years rr_AverageAnnualReturnYear05 5.95%
10 Years rr_AverageAnnualReturnYear10 5.48%
Retail | Thornburg Investment Income Builder Fund | Thornburg Investment Income Builder Fund - Class A | After Taxes on Distributions and Sales  
Prospectus [Line Items] rr_ProspectusLineItems  
1 Year rr_AverageAnnualReturnYear01 8.58%
5 Years rr_AverageAnnualReturnYear05 5.23%
10 Years rr_AverageAnnualReturnYear10 4.93%
Retail | Thornburg Investment Income Builder Fund | Thornburg Investment Income Builder Fund - Class A | Blended Index (reflects no deduction for fees, expenses, or U.S. taxes)  
Prospectus [Line Items] rr_ProspectusLineItems  
1 Year rr_AverageAnnualReturnYear01 15.64%
5 Years rr_AverageAnnualReturnYear05 12.30%
10 Years rr_AverageAnnualReturnYear10 10.36%
Retail | Thornburg Investment Income Builder Fund | Thornburg Investment Income Builder Fund - Class C  
Prospectus [Line Items] rr_ProspectusLineItems  
Trading Symbol dei_TradingSymbol TIBCX
Maximum Sales Charge Imposed on Purchases (as a percentage of Offering Price) rr_MaximumSalesChargeImposedOnPurchasesOverOfferingPrice none
Maximum Deferred Sales Charge (as a percentage) rr_MaximumDeferredSalesChargeOverOther 1.00% [27]
Management Fees (as a percentage of Assets) rr_ManagementFeesOverAssets 0.70%
Distribution and Service (12b-1) Fees rr_DistributionAndService12b1FeesOverAssets 1.00%
Other Expenses (as a percentage of Assets): rr_OtherExpensesOverAssets 0.20% [25]
Acquired Fund Fees and Expenses rr_AcquiredFundFeesAndExpensesOverAssets 0.05%
Expenses (as a percentage of Assets) rr_ExpensesOverAssets 1.95% [26]
Expense Example, with Redemption, 1 Year rr_ExpenseExampleYear01 $ 298
Expense Example, with Redemption, 3 Years rr_ExpenseExampleYear03 612
Expense Example, with Redemption, 5 Years rr_ExpenseExampleYear05 1,052
Expense Example, with Redemption, 10 Years rr_ExpenseExampleYear10 2,275
Expense Example, No Redemption, 1 Year rr_ExpenseExampleNoRedemptionYear01 198
Expense Example, No Redemption, 3 Years rr_ExpenseExampleNoRedemptionYear03 612
Expense Example, No Redemption, 5 Years rr_ExpenseExampleNoRedemptionYear05 1,052
Expense Example, No Redemption, 10 Years rr_ExpenseExampleNoRedemptionYear10 $ 2,275
1 Year rr_AverageAnnualReturnYear01 18.10%
5 Years rr_AverageAnnualReturnYear05 8.16%
10 Years rr_AverageAnnualReturnYear10 7.22%
Retail | Thornburg Investment Income Builder Fund | Thornburg Investment Income Builder Fund - Class C | Blended Index (reflects no deduction for fees, expenses, or U.S. taxes)  
Prospectus [Line Items] rr_ProspectusLineItems  
1 Year rr_AverageAnnualReturnYear01 15.64%
5 Years rr_AverageAnnualReturnYear05 12.30%
10 Years rr_AverageAnnualReturnYear10 10.36%
Retail | Thornburg Investment Income Builder Fund | Thornburg Investment Income Builder Fund - Class I  
Prospectus [Line Items] rr_ProspectusLineItems  
Trading Symbol dei_TradingSymbol TIBIX
Maximum Sales Charge Imposed on Purchases (as a percentage of Offering Price) rr_MaximumSalesChargeImposedOnPurchasesOverOfferingPrice none
Maximum Deferred Sales Charge (as a percentage) rr_MaximumDeferredSalesChargeOverOther none
Management Fees (as a percentage of Assets) rr_ManagementFeesOverAssets 0.70%
Distribution and Service (12b-1) Fees rr_DistributionAndService12b1FeesOverAssets none
Other Expenses (as a percentage of Assets): rr_OtherExpensesOverAssets 0.19% [25]
Acquired Fund Fees and Expenses rr_AcquiredFundFeesAndExpensesOverAssets 0.05%
Expenses (as a percentage of Assets) rr_ExpensesOverAssets 0.94% [26]
Expense Example, with Redemption, 1 Year rr_ExpenseExampleYear01 $ 96
Expense Example, with Redemption, 3 Years rr_ExpenseExampleYear03 300
Expense Example, with Redemption, 5 Years rr_ExpenseExampleYear05 520
Expense Example, with Redemption, 10 Years rr_ExpenseExampleYear10 $ 1,155
1 Year rr_AverageAnnualReturnYear01 20.29%
5 Years rr_AverageAnnualReturnYear05 9.25%
10 Years rr_AverageAnnualReturnYear10 8.31%
Retail | Thornburg Investment Income Builder Fund | Thornburg Investment Income Builder Fund - Class I | Blended Index (reflects no deduction for fees, expenses, or U.S. taxes)  
Prospectus [Line Items] rr_ProspectusLineItems  
1 Year rr_AverageAnnualReturnYear01 15.64%
5 Years rr_AverageAnnualReturnYear05 12.30%
10 Years rr_AverageAnnualReturnYear10 10.36%
Retail | Thornburg Summit Fund  
Prospectus [Line Items] rr_ProspectusLineItems  
Risk/Return [Heading] rr_RiskReturnHeading Summit Fund
Objective [Heading] rr_ObjectiveHeading Investment Goal
Objective, Primary [Text Block] rr_ObjectivePrimaryTextBlock

The Fund seeks to grow real wealth over time.
Expense [Heading] rr_ExpenseHeading Fees and Expenses of the Fund
Expense Narrative [Text Block] rr_ExpenseNarrativeTextBlock

This table describes the fees and expenses that you may pay if you buy and hold shares of the Fund. You may qualify for discounts from the sales charges applicable to Class A shares if you or other qualifying account holders invest, or agree to invest in the future, at least $50,000 in the Thornburg Funds. More information about this and other discounts and sales charge waivers is available from your financial intermediary, in the Prospectus under the captions “Class A Sales Charge Waivers,” beginning on page 146, and “Appendix A – Sales Charge Waivers Offered by Financial Intermediaries,” beginning on page 200, and in the Statement of Additional Information under the caption “Additional Information Respecting Purchase and Redemption of Shares,” beginning on page 108.
Shareholder Fees Caption [Text] rr_ShareholderFeesCaption Shareholder Fees (fees paid directly from your investment)
Operating Expenses Caption [Text] rr_OperatingExpensesCaption Annual Fund Operating Expenses (expenses that you pay each year as a percentage of the value of your investment)
Fee Waiver or Reimbursement over Assets, Date of Termination rr_FeeWaiverOrReimbursementOverAssetsDateOfTermination February 1, 2023
Portfolio Turnover [Heading] rr_PortfolioTurnoverHeading Portfolio Turnover.
Portfolio Turnover [Text Block] rr_PortfolioTurnoverTextBlock

The Fund pays transaction costs, such as commissions, when it buys and sells securities (or “turns over”) its portfolio. A higher portfolio turnover rate may indicate higher transaction costs and may result in higher taxes when Fund shares are held in a taxable account. These costs, which are not reflected in Annual Fund Operating Expenses or in the Example, affect the Fund’s performance. During the most recent fiscal year, the Fund’s portfolio turnover rate was 155.26% of the average value of its portfolio.
Portfolio Turnover, Rate rr_PortfolioTurnoverRate 155.26%
Expense Breakpoint Discounts [Text] rr_ExpenseBreakpointDiscounts You may qualify for discounts from the sales charges applicable to Class A shares if you or other qualifying account holders invest, or agree to invest in the future, at least $50,000 in the Thornburg Funds.
Expense Breakpoint, Minimum Investment Required [Amount] rr_ExpenseBreakpointMinimumInvestmentRequiredAmount $ 50,000
Expense Example [Heading] rr_ExpenseExampleHeading Example.
Expense Example Narrative [Text Block] rr_ExpenseExampleNarrativeTextBlock

This Example is intended to help you compare the cost of investing in the Fund with the cost of investing in other mutual funds.

The Example assumes that you invest $10,000 in the Fund for the time periods indicated and then redeem all of your shares at the end of those periods. The Example also assumes that your investment has a 5% return each year, dividends and distributions are reinvested, and that the Fund’s operating expenses remain the same. Although your actual costs may be higher or lower, based on these assumptions (and giving effect to fee waivers and expense reimbursements in the first year) your costs would be:
Strategy [Heading] rr_StrategyHeading Principal Investment Strategies
Strategy Narrative [Text Block] rr_StrategyNarrativeTextBlock

The Fund seeks to grow real wealth over time. “Real wealth” for this purpose is a mix of capital appreciation and current income that is intended to exceed the rate of inflation. While the Fund seeks to achieve its goal over a variety of different market environments by selecting investments from a range of asset classes, the value of an investment in the Fund will fluctuate and the Fund may not achieve its goal in every environment or in all environments. Under normal conditions the Fund’s investments are expected to emphasize long positions in equity securities and fixed income obligations, though the Fund may also invest a significant amount of its assets in short positions in equity securities and fixed income obligations, in commodities-related investments, in derivative instruments, in currencies, and in cash or cash equivalents. There are no specific percentage limitations on the amount of the Fund’s portfolio that may be invested in a particular asset class, and the proportions of the Fund’s assets that are invested in the respective asset classes are expected to vary over time and from time to time depending upon Thornburg’s perceptions of which types of investments represent better values and opportunities to achieve the Fund’s investment goal.

With respect to its equity investments, the Fund may invest in any stock or equity security, including common stocks, preferred stocks, convertible securities, warrants, depositary receipts, publicly traded real estate investment trusts, and shares in exchange traded funds. The Fund may invest in companies of any size. The Fund’s portfolio may include investments in United States issuers and the securities of issuers domiciled outside the United States, including developing countries. The relative proportions of the Fund’s U.S. and foreign investments will vary over time depending upon Thornburg’s view of specific investment opportunities and macroeconomic factors.

With respect to its fixed income investments, the Fund expects that under normal market conditions its investments will include the following types of obligations, which may be of any quality and of any maturity:

•bonds and other debt obligations issued by domestic and foreign companies of any size (including lower-rated “high yield” or “junk” bonds);

•mortgage-backed securities and other asset-backed securities;

•convertible debt obligations;

•obligations issued by foreign governments (including developing countries);

•collateralized mortgage obligations (“CMOs”), collateralized debt obligations (“CDOs”), collateralized bond obligations (“CBOs”), and collateralized loan obligations (“CLOs”);

•obligations of the U.S. government and its agencies and sponsored enterprises;

•zero coupon bonds and “stripped” securities (including both income only and principal only securities); and

•taxable municipal obligations and participations in municipal obligations.

The Fund’s investments may include both long and short positions. A short sale involves the sale by the Fund of a security that the Fund does not own. The Fund borrows the security that it intends to sell from a broker or other institution, and at a later date the Fund completes the short sale by purchasing that same security on the open market and delivering it to the lending institution. The Fund may also seek to achieve short exposure to an investment through the use of derivative instruments, Allocating the Fund’s portfolio among long and short positions is intended to permit the Fund to pursue its investment goal with lower volatility relative to broad-based securities market indices. While the Fund expects under normal conditions to invest a larger portion of its portfolio in long positions than short positions, the relative proportions of long and short equity investments will vary, and its short positions may represent a significant portion of the Fund’s portfolio during some periods.

With respect to its commodities-related investments, the Fund may invest in exchange traded funds or in other, similar investment vehicles that invest in commodities, and the Fund may invest in commodity-linked derivative instruments whose value is based on the value of an underlying commodity or commodity index, such as commodity futures contracts, commodity forward contracts, and commodity options contracts. The Fund may also seek to obtain exposure to the investment returns of commodities markets by investing in equity and debt securities of companies that operate commodities-based businesses.

The Fund’s investments are determined by individual issuer and industry analysis. Investment decisions are based on domestic and international economic developments, outlooks for securities markets, interest rates and inflation, the supply and demand for equity and debt securities, and analysis of specific issuers. The Fund ordinarily acquires and holds debt obligations for investment rather than for realization of gains by short-term trading on market fluctuations. However, the Fund may dispose of any such security prior to its scheduled maturity to enhance income or reduce loss or to change the portfolio’s average maturity, and the Fund may dispose of any of its investments if Thornburg has identified a better investment opportunity, in response to changes in the conditions or business of the investment’s issuer or changes in overall market conditions, if Thornburg has a target price for the investment and that target price has been achieved, or if, in Thornburg’s opinion, the investment no longer serves to achieve the Fund’s investment goals.

The Fund may also purchase or sell futures contracts or purchase or sell interest rate swaps or credit default swaps to hedge against a decline in the value of the Fund’s other investments, to obtain investment exposure to a particular asset class, or to establish a short position with respect to an investment.
Risk [Heading] rr_RiskHeading Principal Investment Risks
Risk Narrative [Text Block] rr_RiskNarrativeTextBlock

An investment in the Fund is not a deposit in any bank and is not insured or guaranteed by the Federal Deposit Insurance Corporation or any other governmental agency. Accordingly, the loss of money is a risk of investing in the Fund. The value of the Fund’s shares varies from day to day and over time, and when you sell your shares they may be worth less than what you paid for them. The following is a summary of the principal risks of investing in the Fund.

Management Risk – The Fund is an actively managed portfolio, and the value of the Fund may be reduced or the Fund may otherwise be unsuccessful in pursuing its investment goal if Thornburg pursues unsuccessful investments or fails to correctly identify risks affecting the broad economy or specific issuers in which the Fund invests.

Market and Economic Risk – The value of the Fund’s investments may decline and its share value may be reduced due to changes in general economic and market conditions. The value of a security may change in response to developments affecting entire economies, markets or industries, including changes in interest rates, political and legal developments, and general market volatility. This effect is typically more pronounced for lower-rated and unrated debt obligations (including particularly “junk” or “high yield” bonds), the value of which may fluctuate more significantly in response to poor economic growth or other changes in market conditions, political, economic and legal developments. Additionally, because the Fund has to accrue income on zero coupon bonds on a current basis even though the Fund does not receive the income from those bonds currently in cash, zero coupon bonds subject the Fund to the risk of having to generate cash from other sources (including through the sale of portfolio securities) in order to make required distributions of the income accrued from its investments in zero coupon bonds.

Equity Risk – The value of the Fund’s equity investments may fluctuate significantly over time in response to factors affecting individual issuers, particular industries, or the market as a whole. Additionally, common stock ranks below preferred stock and debt securities in claims for dividends and for assets of a company in a liquidation or bankruptcy.

Risks Affecting Specific Issuers – The value of an equity security or debt obligation may decline in response to developments affecting the specific issuer of the security or obligation, even if the overall industry or economy is unaffected.

These developments may include a variety of factors, including but not limited to management issues or other corporate disruption, a decline in revenues or profitability, an increase in costs, or an adverse effect on the issuer’s competitive position.

Foreign Investment Risk – Investments in securities of foreign issuers and in depositary receipts may involve risks including adverse fluctuations in currency exchange rates, political instability, confiscations, taxes or restrictions on currency exchange, difficulty in selling foreign investments, and reduced legal protection. In addition, some foreign government debt obligations may be subject to default, delays in payment, adverse legislation or government action, or could be downgraded by ratings agencies.

Developing Country Risk – The risks which may affect investments in foreign issuers (see “Foreign Investment Risk,” above) may be more pronounced for investments in developing countries because the economies of those countries are usually less diversified, communications, transportation and economic infrastructures are less developed, and developing countries ordinarily have less established legal, political, business and social frameworks. At times the prices of equity securities or debt obligations of a developing country issuer may be extremely volatile. An issuer domiciled in a developed country may be similarly affected by these developing country risks to the extent that the issuer conducts a significant percentage of its business in developing countries.

Foreign Currency Risk – Fluctuations in currency exchange rates can adversely affect the value of the Fund’s foreign investments. Such fluctuations may occur for a number of reasons, including market and economic conditions, or a government’s decision to devalue its currency or impose currency controls.

Small and Mid-Cap Company Risk – Investments in small capitalization companies and mid-capitalization companies may involve additional risks, which may be relatively higher with smaller companies. These additional risks may result from limited product lines, more limited access to markets and financial resources, greater vulnerability to competition and changes in markets, lack of management depth, increased volatility in share price, and possible difficulties in valuing or selling these investments.

Short Sale Risk – A short sale involves the sale by the Fund of a security that the Fund has borrowed, but does not own, in anticipation of purchasing that same security at a lower price in the future in order to close the short position. If the value of the borrowed security increases between the date the Fund enters into the short sale and the date that the Fund buys that security to cover its short position, the Fund may experience a loss.

Credit Risk – If debt obligations held by the Fund are downgraded by ratings agencies or go into default, or if management action, legislation or other government action reduces the ability of issuers to pay principal and interest when due, the value of those obligations may decline and the Fund’s share value and any dividends paid by the Fund may be reduced. Because the ability of an issuer of a lower-rated or unrated debt obligation to pay principal and interest when due is typically less certain than for an issuer of a higher-rated debt obligation, lower-rated and unrated debt obligations are generally more vulnerable than higher-rated debt obligations to default, to ratings downgrades, and to liquidity risk. Debt obligations backed by so-called “subprime” mortgages may also be subject to a greater risk of default or downgrade. Debt obligations issued by the U.S. government or its agencies, instrumentalities and government sponsored enterprises are also subject to credit risk. Securities backed by the full faith and credit of the U.S. government, such as U.S. Treasury obligations, are commonly regarded as having small exposure to credit risk. Obligations of certain U.S. agencies, instrumentalities and enterprises (sometimes referred to as “agency obligations”) are not direct obligations of the U.S. government, may not be backed by the full faith and credit of the U.S. government, and may have a greater exposure to credit risk. The inability of an issuer to pay principal and interest on its debt obligations when due, or the downgrading of an issuer’s debt obligations by ratings agencies, may adversely affect the market’s perceptions of the issuer’s financial strength and may therefore result in declines in the issuer’s stock price.

High Yield Risk – Debt obligations that are rated below investment grade and unrated obligations of similar credit quality (commonly referred to as “junk” or “high yield” bonds) may have a substantial risk of loss. These obligations are generally considered to be speculative with respect to the issuer’s ability to pay interest and principal when due. These obligations may be subject to greater price volatility than investment grade obligations, and their prices may decline significantly in periods of general economic difficulty or in response to adverse publicity, changes in investor perceptions or other factors. These obligations may also be subject to greater liquidity risk.

Interest Rate Risk – When interest rates increase, the value of the Fund’s investments in debt obligations may decline and the Fund’s share value may be reduced. This effect is typically more pronounced for intermediate and longer-term debt obligations. This effect is also typically more pronounced for zero coupon bonds and mortgage- and other asset-backed securities, the value of which may fluctuate more significantly in response to interest rate changes. When interest rates decrease, the Fund’s dividends, if any, may decline.

 

Prepayment and Extension Risk – When market interest rates decline, certain debt obligations held by the Fund may be repaid more quickly than anticipated, requiring the Fund to reinvest the proceeds of those repayments in obligations which bear a lower interest rate. Conversely, when market interest rates increase, certain debt obligations held by the Fund may be repaid more slowly than anticipated, causing assets of the Fund to remain invested in relatively lower yielding obligations. These risks may be more pronounced for the Fund’s investments in mortgage-backed and asset-backed securities.

Liquidity Risk – Due to a lack of demand in the marketplace or other factors, the Fund may not be able to sell some or all of the investments promptly, or may only be able to sell investments at less than desired prices. This risk may be more pronounced for the Fund’s investments in developing countries. Additionally, the market for lower-rated and unrated debt obligations (including particularly “junk” or “high yield” bonds) and debt obligations backed by so-called “subprime” mortgages may be less liquid than the market for other obligations, making it difficult for the Fund to value its investment in a lower-rated or unrated obligation or to sell the investment in a timely manner or at an acceptable price.

Inflation Risk – Although the Fund seeks to generate capital appreciation and current income that exceeds the rate of inflation over a variety of different market environments, there is no guarantee that the Fund will be able to do so at all times. If at any time the rate of inflation exceeds Thornburg’s expectations, or if for other reasons the Fund’s portfolio is unsuccessful in producing a mix of capital appreciation and current income that exceeds the rate of inflation, the Fund may not achieve its goal.

Structured Products Risk – Investments in securities that are backed by, or represent interests in, an underlying pool of securities or other assets, including investments in mortgage- and asset-backed securities and in CMOs, CDOs and CLOS, involve risks associated with the underlying assets (e.g., the risks of default by mortgagors whose mortgages are included in a mortgage-backed security or CMO), and may also involve different or greater risks, including the risk that distributions from the underlying assets will be inadequate to make interest or other payments to the Fund, the risk that the issuer of the securities will fail to administer the underlying assets properly or become insolvent, prepayment and extension risk, and the risk that the securities will be less liquid than other Fund investments.

Commodities-Related Investment Risk – Investments that expose the Fund to the commodities market, such as commodity-linked derivatives instruments or exchange traded funds or other investment vehicles that invest in commodities, may subject the Fund to greater volatility than investments in other securities. The value of a commodity-related investment may be affected by changes in overall market movements, commodity index volatility, changes in interest rates, risks affecting derivatives when used to obtain commodities exposure, or factors affecting a particular industry or commodity.

Real Estate Risk – The Fund’s investments in publicly traded real estate investment trusts (“REITs”) are subject to risks affecting real estate investments generally (including market conditions, competition, property obsolescence, changes in interest rates and casualty to real estate), as well as risks specifically affecting REITs (the quality and skill of REIT management and the internal expenses of the REIT).

Derivatives Risk – The Fund’s investments in futures, interest rate swaps, and credit default swaps involve the risks associated with the securities or other assets underlying those derivatives, including the risk of changes in the value of the underlying assets between the date that the Fund enters into the derivatives transaction and the date that the Fund closes out that transaction. The Fund’s investments in futures, interest rate swaps, and credit default swaps also involve the risk that the other party to the transaction will be unable or unwilling to perform its obligations to the Fund, that the Fund will be unable to sell or close its positions in such derivatives or will be delayed in doing so, and that the Fund will have difficulty valuing such derivatives.

Cybersecurity and Operational Risk – Operational failures, cyber-attacks or other disruptions that affect the Fund’s service providers, the Fund’s counterparties, other market participants or the issuers of securities held by the Fund may adversely affect the Fund and its shareholders, including by causing losses for the Fund or impairing Fund operations.

Additional information about Fund investments, investment strategies and risks of investing in the Fund appears below beginning on page 118 of the Prospectus.
Risk Lose Money [Text] rr_RiskLoseMoney Accordingly, the loss of money is a risk of investing in the Fund.
RIsk Not Insured [Text] rr_RiskNotInsured An investment in the Fund is not a deposit in any bank and is not insured or guaranteed by the Federal Deposit Insurance Corporation or any other governmental agency.
Bar Chart and Performance Table [Heading] rr_BarChartAndPerformanceTableHeading Past Performance of the Fund
Performance Narrative [Text Block] rr_PerformanceNarrativeTextBlock

The following information provides some indication of the risks of investing in Summit Fund by showing how the Fund’s investment results vary from year to year. The bar chart shows how the annual total returns for Class I shares of the Fund have been different in each full year shown. The average annual total return figures compare Class I share performance to the Blended Benchmark, comprised of 60% MSCI All Country (AC) World Index, which represents a broad measure of both domestic and foreign equity market performance, and 40% Bloomberg Barclays Global Aggregate Bond Index, which

provides a broad-based measure of the global investment-grade fixed-rate debt markets. Past performance (before and after taxes) is not necessarily an indication of how the Fund will perform in the future. The performance information shown is as of the calendar year ended December 31, 2021. Updated performance information may be obtained on the Thornburg website at Thornburg.com or by calling 1-800-847-0200.
Performance Information Illustrates Variability of Returns [Text] rr_PerformanceInformationIllustratesVariabilityOfReturns The following information provides some indication of the risks of investing in Summit Fund by showing how the Fund’s investment results vary from year to year.
Performance Availability Phone [Text] rr_PerformanceAvailabilityPhone 1-800-847-0200
Performance Availability Website Address [Text] rr_PerformanceAvailabilityWebSiteAddress Thornburg.com
Performance Past Does Not Indicate Future [Text] rr_PerformancePastDoesNotIndicateFuture Past performance (before and after taxes) is not necessarily an indication of how the Fund will perform in the future.
Bar Chart [Heading] rr_BarChartHeading Annual Total Returns – Class I Shares
Bar Chart Closing [Text Block] rr_BarChartClosingTextBlock

Total
Returns

Quarter
ended

Highest Quarterly Results

17.10%

6/30/2020

Lowest Quarterly Results

(9.27)%

3/31/2020
Performance Table Heading rr_PerformanceTableHeading Average Annual Total Returns (periods ended 12-31-21)
Performance Table Uses Highest Federal Rate rr_PerformanceTableUsesHighestFederalRate After-tax returns are calculated using the highest historical individual federal marginal income tax rates, and do not reflect state or local income taxes.
Performance Table Not Relevant to Tax Deferred rr_PerformanceTableNotRelevantToTaxDeferred Actual after-tax returns depend on an investor’s own tax situation and may differ from the returns shown, and after-tax returns shown are not relevant to investors who hold their Fund shares through tax-deferred arrangements, such as 401(k) plans or individual retirement accounts.
Performance Table Closing [Text Block] rr_PerformanceTableClosingTextBlock

After-tax returns are calculated using the highest historical individual federal marginal income tax rates, and do not reflect state or local income taxes. Actual after-tax returns depend on an investor’s own tax situation and may differ from the returns shown, and after-tax returns shown are not relevant to investors who hold their Fund shares through tax-deferred arrangements, such as 401(k) plans or individual retirement accounts.
Retail | Thornburg Summit Fund | Thornburg Summit Fund - Class A  
Prospectus [Line Items] rr_ProspectusLineItems  
Trading Symbol dei_TradingSymbol TSAMX
Maximum Sales Charge Imposed on Purchases (as a percentage of Offering Price) rr_MaximumSalesChargeImposedOnPurchasesOverOfferingPrice 4.50%
Maximum Deferred Sales Charge (as a percentage) rr_MaximumDeferredSalesChargeOverOther none [28]
Management Fees (as a percentage of Assets) rr_ManagementFeesOverAssets 0.75%
Distribution and Service (12b-1) Fees rr_DistributionAndService12b1FeesOverAssets 0.25%
Component1 Other Expenses rr_Component1OtherExpensesOverAssets 0.02% [29]
Component2 Other Expenses rr_Component2OtherExpensesOverAssets none [29]
Component3 Other Expenses rr_Component3OtherExpensesOverAssets 0.43% [29]
Acquired Fund Fees and Expenses rr_AcquiredFundFeesAndExpensesOverAssets 0.02%
Expenses (as a percentage of Assets) rr_ExpensesOverAssets 1.47%
Fee Waiver or Reimbursement rr_FeeWaiverOrReimbursementOverAssets (0.19%) [30]
Net Expenses (as a percentage of Assets) rr_NetExpensesOverAssets 1.28%
Expense Example, with Redemption, 1 Year rr_ExpenseExampleYear01 $ 575
Expense Example, with Redemption, 3 Years rr_ExpenseExampleYear03 876
Expense Example, with Redemption, 5 Years rr_ExpenseExampleYear05 1,199
Expense Example, with Redemption, 10 Years rr_ExpenseExampleYear10 $ 2,113
Retail | Thornburg Summit Fund | Thornburg Summit Fund - Class I  
Prospectus [Line Items] rr_ProspectusLineItems  
Trading Symbol dei_TradingSymbol TSUMX
Maximum Sales Charge Imposed on Purchases (as a percentage of Offering Price) rr_MaximumSalesChargeImposedOnPurchasesOverOfferingPrice none
Maximum Deferred Sales Charge (as a percentage) rr_MaximumDeferredSalesChargeOverOther none
Management Fees (as a percentage of Assets) rr_ManagementFeesOverAssets 0.75%
Distribution and Service (12b-1) Fees rr_DistributionAndService12b1FeesOverAssets none
Component1 Other Expenses rr_Component1OtherExpensesOverAssets 0.02% [29]
Component2 Other Expenses rr_Component2OtherExpensesOverAssets none [29]
Component3 Other Expenses rr_Component3OtherExpensesOverAssets 0.43% [29]
Acquired Fund Fees and Expenses rr_AcquiredFundFeesAndExpensesOverAssets 0.02%
Expenses (as a percentage of Assets) rr_ExpensesOverAssets 1.22%
Fee Waiver or Reimbursement rr_FeeWaiverOrReimbursementOverAssets (0.19%) [30]
Net Expenses (as a percentage of Assets) rr_NetExpensesOverAssets 1.03%
Expense Example, with Redemption, 1 Year rr_ExpenseExampleYear01 $ 105
Expense Example, with Redemption, 3 Years rr_ExpenseExampleYear03 368
Expense Example, with Redemption, 5 Years rr_ExpenseExampleYear05 652
Expense Example, with Redemption, 10 Years rr_ExpenseExampleYear10 $ 1,461
Annual Return 2020 rr_AnnualReturn2020 27.78%
Annual Return 2021 rr_AnnualReturn2021 14.64%
Highest Quarterly Return, Label rr_HighestQuarterlyReturnLabel Highest Quarterly Results
Highest Quarterly Return, Date rr_BarChartHighestQuarterlyReturnDate Jun. 30, 2020
Highest Quarterly Return rr_BarChartHighestQuarterlyReturn 17.10%
Lowest Quarterly Return, Label rr_LowestQuarterlyReturnLabel Lowest Quarterly Results
Lowest Quarterly Return, Date rr_BarChartLowestQuarterlyReturnDate Mar. 31, 2020
Lowest Quarterly Return rr_BarChartLowestQuarterlyReturn (9.27%)
1 Year rr_AverageAnnualReturnYear01 14.64%
Since Inception rr_AverageAnnualReturnSinceInception 18.23%
Inception Date rr_AverageAnnualReturnInceptionDate Mar. 01, 2019
Retail | Thornburg Summit Fund | Thornburg Summit Fund - Class I | After Taxes on Distributions  
Prospectus [Line Items] rr_ProspectusLineItems  
1 Year rr_AverageAnnualReturnYear01 7.51%
Since Inception rr_AverageAnnualReturnSinceInception 14.44%
Retail | Thornburg Summit Fund | Thornburg Summit Fund - Class I | After Taxes on Distributions and Sales  
Prospectus [Line Items] rr_ProspectusLineItems  
1 Year rr_AverageAnnualReturnYear01 9.16%
Since Inception rr_AverageAnnualReturnSinceInception 12.74%
Retail | Thornburg Summit Fund | Thornburg Summit Fund - Class I | Blended Index (reflects no deduction for fees, expenses, or U.S. taxes)  
Prospectus [Line Items] rr_ProspectusLineItems  
1 Year rr_AverageAnnualReturnYear01 8.78%
Since Inception rr_AverageAnnualReturnSinceInception 11.88%
Retail | Thornburg Limited Term U.S. Government Fund  
Prospectus [Line Items] rr_ProspectusLineItems  
Risk/Return [Heading] rr_RiskReturnHeading Limited Term U.S. Government Fund
Objective [Heading] rr_ObjectiveHeading Investment Goal
Objective, Primary [Text Block] rr_ObjectivePrimaryTextBlock

The primary goal of Limited Term U.S. Government Fund is to provide as high a level of current income as is consistent, in the view of the Fund’s investment advisor, with safety of capital.
Objective, Secondary [Text Block] rr_ObjectiveSecondaryTextBlock

As a secondary goal, the Fund seeks to reduce changes in its share price compared to longer term portfolios.
Expense [Heading] rr_ExpenseHeading Fees and Expenses of the Fund
Expense Narrative [Text Block] rr_ExpenseNarrativeTextBlock

This table describes the fees and expenses that you may pay if you buy and hold shares of the Fund. You may qualify for discounts from the sales charges applicable to Class A shares if you or other qualifying account holders invest, or agree to invest in the future, at least $50,000 in the Thornburg Funds. More information about this and other discounts and sales charge waivers is available from your financial intermediary, in the Prospectus under the captions “Class A Sales Charge Waivers,” beginning on page 146, and “Appendix A – Sales Charge Waivers Offered by Financial Intermediaries,” beginning on page 200, and in the Statement of Additional Information under the caption “Additional Information Respecting Purchase and Redemption of Shares,” beginning on page 108.
Shareholder Fees Caption [Text] rr_ShareholderFeesCaption Shareholder Fees (fees paid directly from your investment)
Operating Expenses Caption [Text] rr_OperatingExpensesCaption Annual Fund Operating Expenses (expenses that you pay each year as a percentage of the value of your investment)
Fee Waiver or Reimbursement over Assets, Date of Termination rr_FeeWaiverOrReimbursementOverAssetsDateOfTermination February 1, 2023
Portfolio Turnover [Heading] rr_PortfolioTurnoverHeading Portfolio Turnover.
Portfolio Turnover [Text Block] rr_PortfolioTurnoverTextBlock

The Fund pays transaction costs, such as commissions, when it buys and sells securities (or “turns over”) its portfolio. A higher portfolio turnover rate may indicate higher transaction costs and may result in higher taxes when Fund shares are held in a taxable account. These costs, which are not reflected in Annual Fund Operating Expenses or in the Example, affect the Fund’s performance. During the most recent fiscal year, the Fund’s portfolio turnover rate was 9.50% of the average value of its portfolio.
Portfolio Turnover, Rate rr_PortfolioTurnoverRate 9.50%
Expense Breakpoint Discounts [Text] rr_ExpenseBreakpointDiscounts You may qualify for discounts from the sales charges applicable to Class A shares if you or other qualifying account holders invest, or agree to invest in the future, at least $50,000 in the Thornburg Funds.
Expense Breakpoint, Minimum Investment Required [Amount] rr_ExpenseBreakpointMinimumInvestmentRequiredAmount $ 50,000
Expense Example [Heading] rr_ExpenseExampleHeading Example.
Expense Example Narrative [Text Block] rr_ExpenseExampleNarrativeTextBlock

This Example is intended to help you compare the cost of investing in the Fund with the cost of investing in other mutual funds.

The Example assumes that you invest $10,000 in the Fund for the time periods indicated and then redeem all of your shares at the end of those periods. The Example also assumes that your investment has a 5% return each year, dividends and distributions are reinvested, and that the Fund’s operating expenses remain the same. Although your actual costs may be higher or lower, based on these assumptions, your costs would be:
Expense Example, No Redemption Narrative [Text Block] rr_ExpenseExampleNoRedemptionNarrativeTextBlock

You would pay the following expenses if you did not redeem your Class C shares:
Strategy [Heading] rr_StrategyHeading Principal Investment Strategies
Strategy Narrative [Text Block] rr_StrategyNarrativeTextBlock

Thornburg Investment Management, Inc. (“Thornburg”) actively manages the Fund’s portfolio in pursuing the Fund’s investment goals. While Thornburg follows domestic and international economic developments, outlooks for securities markets, interest rates and inflation, the supply and demand for debt obligations, and other factors, the Fund’s investments are determined by individual security analysis. The Fund ordinarily acquires and holds securities for investment rather than for realization of gains by short-term trading on market fluctuations. However, it may dispose of any security before its scheduled maturity to enhance income or reduce loss, to change the portfolio’s average maturity, or to otherwise respond to market conditions.

Limited Term U.S. Government Fund invests at least 80% of its assets in U.S. Government Securities. For this purpose, “U.S. Government Securities” means:

Securities backed by the full faith and credit of the U.S. government, including direct obligations of the U.S. Treasury (such as U.S. Treasury Bonds) and obligations of U.S. government agencies and instrumentalities which are guaranteed by the U.S. Treasury (such as “Ginnie Mae” mortgage-backed certificates issued by the Government National Mortgage Association).

Securities issued or guaranteed by U.S. government agencies, instrumentalities or sponsored enterprises, but which are not backed by the full faith and credit of the U.S. government. These securities include mortgage-backed certificates, collateralized mortgage obligations (“CMOs”), and debentures issued by “Freddie Mac” (Federal Home Loan Mortgage Corporation) and “Fannie Mae” (Federal National Mortgage Association).

U.S. Government Securities include for this purpose repurchase agreements secured by the securities described above, and participations having economic characteristics similar to those securities. “Participations” are undivided interests in pools of securities where the underlying credit support passes through to the participants.

Because the magnitude of changes in the value of interest-bearing obligations is greater for obligations with longer terms given an equivalent change in interest rates, the Fund seeks to reduce changes in its share value by maintaining a portfolio of investments with a dollar-weighted average maturity or expected life of normally less than five years. There is no limitation on the maturity of any specific security the Fund may purchase, and the Fund may sell any security before it matures. The Fund also attempts to reduce changes in share value through credit analysis, selection and diversification.

The Fund ordinarily acquires and holds securities for investment rather than for realization of gains by short-term trading on market fluctuations. However, it may sell an investment prior to its scheduled maturity date to enhance income or reduce loss, to change the portfolio’s average duration or average maturity, to pursue other investment opportunities, in response to changes in the conditions or business of the investment’s issuer or changes in overall market conditions, or if, in Thornburg’s opinion, the investment no longer serves to achieve the Fund’s investment goals.  The objective of preserving capital may prevent the Fund from obtaining the highest yields available.
Risk [Heading] rr_RiskHeading Principal Investment Risks
Risk Narrative [Text Block] rr_RiskNarrativeTextBlock

Although the Fund may acquire obligations issued or guaranteed by the U.S. government and its agencies, instrumentalities and enterprises, neither the Fund’s net asset value nor its dividends are guaranteed by the U.S. government. An investment in the Fund is not a deposit in any bank and is not insured or guaranteed by the Federal Deposit Insurance Corporation or any other government agency. Accordingly, the loss of money is a risk of investing in the Fund. The value of the Fund’s shares and its dividends may fluctuate from day to day and over time, and when you sell your shares they may be worth less than what you paid for them. If your sole objective is preservation of capital, then the Fund may not be suitable for you because the Fund’s share value will fluctuate, including as interest rates change. Investors whose sole objective is preservation of capital may wish to consider a high quality money market fund. The following is a summary of the principal risks of investing in the Fund.

Management Risk – The Fund is an actively managed portfolio, and the value of the Fund may be reduced if Thornburg pursues unsuccessful investments or fails to correctly identify risks affecting the broad economy or specific issuers in which the Fund invests.

Interest Rate Risk – When interest rates increase, the value of the Fund’s investments may decline and the Fund’s share value may be reduced. This effect is typically more pronounced for intermediate and longer-term obligations. This effect is also typically more pronounced for the Fund’s investment in mortgage-backed securities, the value of which may fluctuate more significantly in response to interest rate changes. When interest rates decrease, the Fund’s dividends may decline.

Prepayment and Extension Risk – When market interest rates decline, certain debt obligations held by the Fund may be repaid more quickly than anticipated, requiring the Fund to reinvest the proceeds of those repayments in obligations which bear a lower interest rate. Conversely, when market interest rates increase, certain debt obligations held by the Fund may be repaid more slowly than anticipated, causing assets of the Fund to remain invested in relatively lower yielding obligations. These risks may be more pronounced for the Fund’s investments in mortgage-backed securities.

Credit Risk – All securities owned by the Fund may be subject to default, delays in payment, adverse legislation or other government action, or could be downgraded by ratings agencies, reducing the value of the Fund’s shares. Securities backed by the full faith and credit of the U.S. government, such as U.S. Treasury obligations, are commonly regarded as having small exposure to credit risk. Obligations of certain U.S. government agencies, instrumentalities and government-sponsored enterprises (sometimes referred to as “agency obligations”) are not direct obligations of the United States, may not be backed by the full faith and credit of the U.S. government, and may have a greater exposure to credit risk. Although the U.S. government is required by law to provide credit support for some agency obligations, there is no assurance that the U.S. government would provide financial support for any such obligation on a default by the issuing agency, instrumentality or enterprise in the absence of a legal requirement to do so. As of the date of this Prospectus, securities backed by the full faith and credit of the U.S. government, and securities of U.S. government agencies, instrumentalities and enterprises which may be purchased by the Fund are rated “Aaa” by Moody’s Investors Services or “AA+” by S&P Global Ratings. Ratings agencies may reduce the ratings of any securities in the future.

Market and Economic Risk – The value of the Fund’s investments may decline and its share value may be reduced due to changes in general economic and market conditions. For example, a fall in worldwide demand for U.S. government securities or general economic decline could lower the value of those securities.

Liquidity Risk – Due to a lack of demand in the marketplace or other factors, the Fund may not be able to sell promptly some or all of the obligations that it holds, or may only be able to sell obligations at less than desired prices.

Structured Products Risk – Investments in securities that are backed by, or represent interests in, an underlying pool of securities or other assets, including investments in mortgage-backed securities and in CMOs, involve the risks associated with the underlying assets (e.g., the risk of default by mortgagors whose mortgages are included in a mortgage-backed security or CMO), and may also involve different or greater risks, including the risk that distributions from the underlying assets will be inadequate to make interest or other payments to the Fund, the risk that the issuer of the securities will fail to administer the underlying assets properly or become insolvent, and the risk that the securities will be less liquid than other Fund investments.

Cybersecurity and Operational Risk – Operational failures, cyber-attacks or other disruptions that affect the Fund’s service providers, the Fund’s counterparties, other market participants or the issuers of securities held by the Fund may adversely affect the Fund and its shareholders, including by causing losses for the Fund or impairing Fund operations.

Additional information about Fund investments, investment strategies, and risks of investing in the Fund appears below beginning on page 118 of the Prospectus.
Risk Lose Money [Text] rr_RiskLoseMoney Accordingly, the loss of money is a risk of investing in the Fund.
RIsk Not Insured [Text] rr_RiskNotInsured An investment in the Fund is not a deposit in any bank and is not insured or guaranteed by the Federal Deposit Insurance Corporation or any other government agency.
Bar Chart and Performance Table [Heading] rr_BarChartAndPerformanceTableHeading Past Performance of the Fund
Performance Narrative [Text Block] rr_PerformanceNarrativeTextBlock

The following information provides some indication of the risks of investing in Limited Term U.S. Government Fund by showing how the Fund’s investment results vary from year to year. The bar chart shows how the annual total returns for Class A shares have been different in each full year shown. The average annual total return figures compare Class A, Class C, Class C2 and Class I share performance to the Bloomberg Barclays US Government Intermediate Total Return Index Value Unhedged, a broad measure of market performance. Past performance (before and after taxes) is not necessarily an indication of how the Fund will perform in the future. The performance information shown is as of the calendar year ended December 31, 2021. Updated performance information may be obtained on the Thornburg website at Thornburg.com or by calling 1-800-847-0200.
Performance Information Illustrates Variability of Returns [Text] rr_PerformanceInformationIllustratesVariabilityOfReturns The following information provides some indication of the risks of investing in Limited Term U.S. Government Fund by showing how the Fund’s investment results vary from year to year.
Performance Availability Phone [Text] rr_PerformanceAvailabilityPhone 1-800-847-0200
Performance Availability Website Address [Text] rr_PerformanceAvailabilityWebSiteAddress Thornburg.com
Performance Past Does Not Indicate Future [Text] rr_PerformancePastDoesNotIndicateFuture Past performance (before and after taxes) is not necessarily an indication of how the Fund will perform in the future.
Bar Chart [Heading] rr_BarChartHeading Annual Total Returns – Class A Shares
Bar Chart Does Not Reflect Sales Loads [Text] rr_BarChartDoesNotReflectSalesLoads The sales charge for Class A shares is not reflected in the returns shown in the bar chart above, and the returns would be less if the charge was taken into account.
Bar Chart Closing [Text Block] rr_BarChartClosingTextBlock

Total
Returns

Quarter
ended

Highest Quarterly Results

1.93%

6/30/2011

Lowest Quarterly Results

(1.68)%

3/31/2021

The sales charge for Class A shares is not reflected in the returns shown in the bar chart above, and the returns would be less if the charge was taken into account.
Performance Table Heading rr_PerformanceTableHeading Average Annual Total Returns (periods ended 12-31-21)
Performance Table Uses Highest Federal Rate rr_PerformanceTableUsesHighestFederalRate After-tax returns are calculated using the highest historical individual federal marginal income tax rates, and do not reflect state or local income taxes.
Performance Table Not Relevant to Tax Deferred rr_PerformanceTableNotRelevantToTaxDeferred Actual after-tax returns depend on an investor’s own tax situation and may differ from the returns shown, and after-tax returns shown are not relevant to investors who hold their Fund shares through tax-deferred arrangements, such as 401(k) plans or individual retirement accounts.
Performance Table One Class of after Tax Shown [Text] rr_PerformanceTableOneClassOfAfterTaxShown The after-tax returns shown relate only to Class A shares, and after-tax returns for other share classes will vary.
Performance Table Closing [Text Block] rr_PerformanceTableClosingTextBlock

After-tax returns are calculated using the highest historical individual federal marginal income tax rates, and do not reflect state or local income taxes. Actual after-tax returns depend on an investor’s own tax situation and may differ from the returns shown, and after-tax returns shown are not relevant to investors who hold their Fund shares through tax-deferred arrangements, such as 401(k) plans or individual retirement accounts. The after-tax returns shown relate only to Class A shares, and after-tax returns for other share classes will vary.
Retail | Thornburg Limited Term U.S. Government Fund | Thornburg Limited Term U.S. Government Fund - Class A  
Prospectus [Line Items] rr_ProspectusLineItems  
Trading Symbol dei_TradingSymbol LTUSX
Maximum Sales Charge Imposed on Purchases (as a percentage of Offering Price) rr_MaximumSalesChargeImposedOnPurchasesOverOfferingPrice 2.25%
Maximum Deferred Sales Charge (as a percentage) rr_MaximumDeferredSalesChargeOverOther none [31]
Management Fees (as a percentage of Assets) rr_ManagementFeesOverAssets 0.37%
Distribution and Service (12b-1) Fees rr_DistributionAndService12b1FeesOverAssets 0.25%
Other Expenses (as a percentage of Assets): rr_OtherExpensesOverAssets 0.25%
Expenses (as a percentage of Assets) rr_ExpensesOverAssets 0.87%
Fee Waiver or Reimbursement rr_FeeWaiverOrReimbursementOverAssets
Net Expenses (as a percentage of Assets) rr_NetExpensesOverAssets 0.87%
Expense Example, with Redemption, 1 Year rr_ExpenseExampleYear01 $ 312
Expense Example, with Redemption, 3 Years rr_ExpenseExampleYear03 496
Expense Example, with Redemption, 5 Years rr_ExpenseExampleYear05 696
Expense Example, with Redemption, 10 Years rr_ExpenseExampleYear10 $ 1,273
Annual Return 2012 rr_AnnualReturn2012 2.01%
Annual Return 2013 rr_AnnualReturn2013 (1.87%)
Annual Return 2014 rr_AnnualReturn2014 2.32%
Annual Return 2015 rr_AnnualReturn2015 0.34%
Annual Return 2016 rr_AnnualReturn2016 0.90%
Annual Return 2017 rr_AnnualReturn2017 0.60%
Annual Return 2018 rr_AnnualReturn2018 0.83%
Annual Return 2019 rr_AnnualReturn2019 3.61%
Annual Return 2020 rr_AnnualReturn2020 3.77%
Annual Return 2021 rr_AnnualReturn2021 (1.83%)
Highest Quarterly Return, Label rr_HighestQuarterlyReturnLabel Highest Quarterly Results
Highest Quarterly Return, Date rr_BarChartHighestQuarterlyReturnDate Jun. 30, 2011
Highest Quarterly Return rr_BarChartHighestQuarterlyReturn 1.93%
Lowest Quarterly Return, Label rr_LowestQuarterlyReturnLabel Lowest Quarterly Results
Lowest Quarterly Return, Date rr_BarChartLowestQuarterlyReturnDate Mar. 31, 2021
Lowest Quarterly Return rr_BarChartLowestQuarterlyReturn (1.68%)
1 Year rr_AverageAnnualReturnYear01 (4.06%)
5 Years rr_AverageAnnualReturnYear05 1.07%
10 Years rr_AverageAnnualReturnYear10 0.90%
Retail | Thornburg Limited Term U.S. Government Fund | Thornburg Limited Term U.S. Government Fund - Class A | After Taxes on Distributions  
Prospectus [Line Items] rr_ProspectusLineItems  
1 Year rr_AverageAnnualReturnYear01 (4.52%)
5 Years rr_AverageAnnualReturnYear05 0.44%
10 Years rr_AverageAnnualReturnYear10 0.19%
Retail | Thornburg Limited Term U.S. Government Fund | Thornburg Limited Term U.S. Government Fund - Class A | After Taxes on Distributions and Sales  
Prospectus [Line Items] rr_ProspectusLineItems  
1 Year rr_AverageAnnualReturnYear01 (2.40%)
5 Years rr_AverageAnnualReturnYear05 0.54%
10 Years rr_AverageAnnualReturnYear10 0.38%
Retail | Thornburg Limited Term U.S. Government Fund | Thornburg Limited Term U.S. Government Fund - Class A | Bloomberg Barclays US Government Intermediate Total Return Index Value Unhedged (reflects no deduction for fees, expenses, or taxes)  
Prospectus [Line Items] rr_ProspectusLineItems  
1 Year rr_AverageAnnualReturnYear01 (1.69%)
5 Years rr_AverageAnnualReturnYear05 2.32%
10 Years rr_AverageAnnualReturnYear10 1.68%
Retail | Thornburg Limited Term U.S. Government Fund | Thornburg Limited Term U.S. Government Fund - Class C  
Prospectus [Line Items] rr_ProspectusLineItems  
Trading Symbol dei_TradingSymbol LTUCX
Maximum Sales Charge Imposed on Purchases (as a percentage of Offering Price) rr_MaximumSalesChargeImposedOnPurchasesOverOfferingPrice none
Maximum Deferred Sales Charge (as a percentage) rr_MaximumDeferredSalesChargeOverOther 0.50% [32]
Management Fees (as a percentage of Assets) rr_ManagementFeesOverAssets 0.37%
Distribution and Service (12b-1) Fees rr_DistributionAndService12b1FeesOverAssets 0.50%
Other Expenses (as a percentage of Assets): rr_OtherExpensesOverAssets 0.37%
Expenses (as a percentage of Assets) rr_ExpensesOverAssets 1.24%
Fee Waiver or Reimbursement rr_FeeWaiverOrReimbursementOverAssets
Net Expenses (as a percentage of Assets) rr_NetExpensesOverAssets 1.24%
Expense Example, with Redemption, 1 Year rr_ExpenseExampleYear01 $ 176
Expense Example, with Redemption, 3 Years rr_ExpenseExampleYear03 393
Expense Example, with Redemption, 5 Years rr_ExpenseExampleYear05 681
Expense Example, with Redemption, 10 Years rr_ExpenseExampleYear10 1,500
Expense Example, No Redemption, 1 Year rr_ExpenseExampleNoRedemptionYear01 126
Expense Example, No Redemption, 3 Years rr_ExpenseExampleNoRedemptionYear03 393
Expense Example, No Redemption, 5 Years rr_ExpenseExampleNoRedemptionYear05 681
Expense Example, No Redemption, 10 Years rr_ExpenseExampleNoRedemptionYear10 $ 1,500
1 Year rr_AverageAnnualReturnYear01 (2.67%)
5 Years rr_AverageAnnualReturnYear05 1.04%
10 Years rr_AverageAnnualReturnYear10 0.75%
Retail | Thornburg Limited Term U.S. Government Fund | Thornburg Limited Term U.S. Government Fund - Class C | Bloomberg Barclays US Government Intermediate Total Return Index Value Unhedged (reflects no deduction for fees, expenses, or taxes)  
Prospectus [Line Items] rr_ProspectusLineItems  
1 Year rr_AverageAnnualReturnYear01 (1.69%)
5 Years rr_AverageAnnualReturnYear05 2.32%
10 Years rr_AverageAnnualReturnYear10 1.68%
Retail | Thornburg Limited Term U.S. Government Fund | Thornburg Limited Term U.S. Government Fund - Class C2  
Prospectus [Line Items] rr_ProspectusLineItems  
Trading Symbol dei_TradingSymbol LTUQX
Maximum Sales Charge Imposed on Purchases (as a percentage of Offering Price) rr_MaximumSalesChargeImposedOnPurchasesOverOfferingPrice none
Maximum Deferred Sales Charge (as a percentage) rr_MaximumDeferredSalesChargeOverOther 0.65% [32]
Management Fees (as a percentage of Assets) rr_ManagementFeesOverAssets 0.37%
Distribution and Service (12b-1) Fees rr_DistributionAndService12b1FeesOverAssets 0.65%
Other Expenses (as a percentage of Assets): rr_OtherExpensesOverAssets 2.35%
Expenses (as a percentage of Assets) rr_ExpensesOverAssets 3.37%
Fee Waiver or Reimbursement rr_FeeWaiverOrReimbursementOverAssets (2.13%) [33]
Net Expenses (as a percentage of Assets) rr_NetExpensesOverAssets 1.24%
Expense Example, with Redemption, 1 Year rr_ExpenseExampleYear01 $ 191
Expense Example, with Redemption, 3 Years rr_ExpenseExampleYear03 837
Expense Example, with Redemption, 5 Years rr_ExpenseExampleYear05 1,571
Expense Example, with Redemption, 10 Years rr_ExpenseExampleYear10 3,514
Expense Example, No Redemption, 1 Year rr_ExpenseExampleNoRedemptionYear01 126
Expense Example, No Redemption, 3 Years rr_ExpenseExampleNoRedemptionYear03 837
Expense Example, No Redemption, 5 Years rr_ExpenseExampleNoRedemptionYear05 1,571
Expense Example, No Redemption, 10 Years rr_ExpenseExampleNoRedemptionYear10 $ 3,514
1 Year rr_AverageAnnualReturnYear01 (2.82%)
Since Inception rr_AverageAnnualReturnSinceInception (1.77%)
Inception Date rr_AverageAnnualReturnInceptionDate Oct. 01, 2020
Retail | Thornburg Limited Term U.S. Government Fund | Thornburg Limited Term U.S. Government Fund - Class C2 | Bloomberg Barclays US Government Intermediate Total Return Index Value Unhedged (reflects no deduction for fees, expenses, or taxes)  
Prospectus [Line Items] rr_ProspectusLineItems  
1 Year rr_AverageAnnualReturnYear01 (1.69%)
Since Inception rr_AverageAnnualReturnSinceInception (1.53%)
Retail | Thornburg Limited Term U.S. Government Fund | Thornburg Limited Term U.S. Government Fund - Class I  
Prospectus [Line Items] rr_ProspectusLineItems  
Trading Symbol dei_TradingSymbol LTUIX
Maximum Sales Charge Imposed on Purchases (as a percentage of Offering Price) rr_MaximumSalesChargeImposedOnPurchasesOverOfferingPrice none
Maximum Deferred Sales Charge (as a percentage) rr_MaximumDeferredSalesChargeOverOther none
Management Fees (as a percentage of Assets) rr_ManagementFeesOverAssets 0.37%
Distribution and Service (12b-1) Fees rr_DistributionAndService12b1FeesOverAssets none
Other Expenses (as a percentage of Assets): rr_OtherExpensesOverAssets 0.24%
Expenses (as a percentage of Assets) rr_ExpensesOverAssets 0.61%
Fee Waiver or Reimbursement rr_FeeWaiverOrReimbursementOverAssets
Net Expenses (as a percentage of Assets) rr_NetExpensesOverAssets 0.61%
Expense Example, with Redemption, 1 Year rr_ExpenseExampleYear01 $ 62
Expense Example, with Redemption, 3 Years rr_ExpenseExampleYear03 195
Expense Example, with Redemption, 5 Years rr_ExpenseExampleYear05 340
Expense Example, with Redemption, 10 Years rr_ExpenseExampleYear10 $ 762
1 Year rr_AverageAnnualReturnYear01 (1.58%)
5 Years rr_AverageAnnualReturnYear05 1.67%
10 Years rr_AverageAnnualReturnYear10 1.36%
Retail | Thornburg Limited Term U.S. Government Fund | Thornburg Limited Term U.S. Government Fund - Class I | Bloomberg Barclays US Government Intermediate Total Return Index Value Unhedged (reflects no deduction for fees, expenses, or taxes)  
Prospectus [Line Items] rr_ProspectusLineItems  
1 Year rr_AverageAnnualReturnYear01 (1.69%)
5 Years rr_AverageAnnualReturnYear05 2.32%
10 Years rr_AverageAnnualReturnYear10 1.68%
Retail | Thornburg Limited Term Income Fund  
Prospectus [Line Items] rr_ProspectusLineItems  
Risk/Return [Heading] rr_RiskReturnHeading Limited Term Income Fund
Objective [Heading] rr_ObjectiveHeading Investment Goal
Objective, Primary [Text Block] rr_ObjectivePrimaryTextBlock

The primary goal of Limited Term Income Fund is to provide as high a level of current income as is consistent, in the view of the Fund’s investment advisor, with safety of capital.
Objective, Secondary [Text Block] rr_ObjectiveSecondaryTextBlock

As a secondary goal, the Fund seeks to reduce changes in its share prices compared to longer term portfolios.
Expense [Heading] rr_ExpenseHeading Fees and Expenses of the Fund
Expense Narrative [Text Block] rr_ExpenseNarrativeTextBlock

This table describes the fees and expenses that you may pay if you buy and hold shares of the Fund. You may qualify for discounts from the sales charges applicable to Class A shares if you or other qualifying account holders invest, or agree to invest in the future, at least $50,000 in the Thornburg Funds. More information about this and other discounts and sales charge waivers is available from your financial intermediary, in the Prospectus under the captions “Class A Sales Charge Waivers,” beginning on page 146, and “Appendix A – Sales Charge Waivers Offered by Financial Intermediaries,” beginning on page 200, and in the Statement of Additional Information under the caption “Additional Information Respecting Purchase and Redemption of Shares,” beginning on page 108.
Shareholder Fees Caption [Text] rr_ShareholderFeesCaption Shareholder Fees (fees paid directly from your investment)
Operating Expenses Caption [Text] rr_OperatingExpensesCaption Annual Fund Operating Expenses (expenses that you pay each year as a percentage of the value of your investment)
Fee Waiver or Reimbursement over Assets, Date of Termination rr_FeeWaiverOrReimbursementOverAssetsDateOfTermination February 1, 2023
Portfolio Turnover [Heading] rr_PortfolioTurnoverHeading Portfolio Turnover.
Portfolio Turnover [Text Block] rr_PortfolioTurnoverTextBlock

The Fund pays transaction costs, such as commissions, when it buys and sells securities (or “turns over”) its portfolio. A higher portfolio turnover rate may indicate higher transaction costs and may result in higher taxes when Fund shares are held in a taxable account. These costs, which are not reflected in Annual Fund Operating Expenses or in the Example, affect the Fund’s performance. During the most recent fiscal year, the Fund’s portfolio turnover rate was 33.37% of the average value of its portfolio.
Portfolio Turnover, Rate rr_PortfolioTurnoverRate 33.37%
Expense Breakpoint Discounts [Text] rr_ExpenseBreakpointDiscounts You may qualify for discounts from the sales charges applicable to Class A shares if you or other qualifying account holders invest, or agree to invest in the future, at least $50,000 in the Thornburg Funds
Expense Breakpoint, Minimum Investment Required [Amount] rr_ExpenseBreakpointMinimumInvestmentRequiredAmount $ 50,000
Expense Example [Heading] rr_ExpenseExampleHeading Example.
Expense Example Narrative [Text Block] rr_ExpenseExampleNarrativeTextBlock

This Example is intended to help you compare the cost of investing in the Fund with the cost of investing in other mutual funds.

The Example assumes that you invest $10,000 in the Fund for the time periods indicated and then redeem all of your shares at the end of those periods. The Example also assumes that your investment has a 5% return each year, dividends and distributions are reinvested, and that the Fund’s operating expenses remain the same. Although your actual costs may be higher or lower, based on these assumptions, your costs would be:
Expense Example, No Redemption Narrative [Text Block] rr_ExpenseExampleNoRedemptionNarrativeTextBlock

You would pay the following expenses if you did not redeem your Class C shares:
Strategy [Heading] rr_StrategyHeading Principal Investment Strategies
Strategy Narrative [Text Block] rr_StrategyNarrativeTextBlock

Thornburg Investment Management, Inc. (“Thornburg”) actively manages the Fund’s portfolio in pursuing the Fund’s investment goals. While Thornburg follows domestic and international economic developments, outlooks for securities markets, interest rates and inflation, the supply and demand for debt obligations, and other factors, the Fund’s investments are determined by individual security analysis. The Fund ordinarily acquires and holds securities for investment rather than for realization of gains by short-term trading on market fluctuations. However, it may dispose of any security prior to its scheduled maturity to enhance income or reduce loss, to change the portfolio’s average maturity, or to otherwise respond to current market conditions.

The Fund invests at least 65% of its net assets in (i) obligations of the U.S. government, its agencies and instrumentalities, and (ii) debt obligations rated at the time of purchase in one of the three highest principal long term rating categories of S&P Global Ratings (AAA, AA or A) or Moody’s Investors Services, Inc. (Aaa, Aa or A), or the equivalent three highest short term ratings of those ratings agencies, or, if no credit rating is available, judged to be of comparable quality as determined by Thornburg. The Fund will not invest in any debt obligation rated at the time of purchase lower than BBB by S&P, Baa by Moody’s, of the equivalent short term ratings of those ratings agencies, or, if no credit rating is available, judged to be of comparable quality as determined by Thornburg. The Fund may purchase corporate debt obligations, municipal securities, and commercial paper and bankers’ acceptances, and the Fund may also purchase securities backed by an underlying pool of debt obligations, including mortgage-backed securities, asset-backed securities, collateralized mortgage obligations, and collateralized debt obligations (sometimes referred to collectively as “structured products”). The Fund may purchase foreign securities of the same types and quality as the domestic securities it purchases when Thornburg believes these investments are consistent with the Fund’s objectives.

Because the magnitude of changes in the value of interest-bearing obligations is greater for obligations with longer terms given an equivalent change in interest rates, the Fund seeks to reduce changes in its share value by maintaining a portfolio of investments with a dollar-weighted average maturity or expected life of normally less than five years. As a result, the Fund also maintains a portfolio of investments having a dollar-weighted average effective duration of normally no more than five years. Duration is a measure of estimated sensitivity to interest rate changes. A portfolio with a longer average effective duration will typically be more sensitive to interest rate changes than a portfolio with a shorter average effective duration. Duration is commonly expressed as a number, which is the expected percentage change in an obligation’s price upon a 1% change in interest rates. For example,

an obligation with a duration of 5 would be expected to change in price by approximately 5% in response to a 1% change in interest rates. During temporary periods the Fund’s portfolio maturity and average effective duration may be reduced for defensive purposes. There is no limitation on the maturity of any specific security the Fund may purchase, and the Fund may sell any security before it matures. The Fund also attempts to reduce changes in share value through credit analysis, selection and diversification.

The Fund ordinarily acquires and holds securities for investment rather than for realization of gains by short-term trading on market fluctuations. However, it may sell an investment prior to its scheduled maturity date to enhance income or reduce loss, to change the portfolio’s average duration or average maturity, to pursue other investment opportunities, in response to changes in the conditions or business of the investment’s issuer or changes in overall market conditions, or if, in Thornburg’s opinion, the investment no longer serves to achieve the Fund’s investment goals.  The objective of preserving capital may prevent the Fund from obtaining the highest yields available.
Risk [Heading] rr_RiskHeading Principal Investment Risks
Risk Narrative [Text Block] rr_RiskNarrativeTextBlock

Although the Fund may acquire obligations issued or guaranteed by the U.S. government and its agencies, instrumentalities and enterprises, neither the Fund’s net asset value nor its dividends are guaranteed by the U.S. government. An investment in the Fund is not a deposit in any bank and is not insured or guaranteed by the Federal Deposit Insurance Corporation or any other government agency. Accordingly, the loss of money is a risk of investing in the Fund. The value of the Fund’s shares and its dividends may fluctuate from day to day and over time, and when you sell your shares they may be worth less than what you paid for them. If your sole objective is preservation of capital, then the Fund may not be suitable for you because the Fund’s share value will fluctuate, including as interest rates change. Investors whose sole objective is preservation of capital may wish to consider a high quality money market fund. The following is a summary of the principal risks of investing in the Fund.

Management Risk – The Fund is an actively managed portfolio, and the value of the Fund may be reduced if Thornburg pursues unsuccessful investments or fails to correctly identify risks affecting the broad economy or specific issuers in which the Fund invests.

Interest Rate Risk – When interest rates increase, the value of the Fund’s investments may decline and the Fund’s share value may be reduced. This effect is typically more pronounced for intermediate and longer-term obligations. This effect is also typically more pronounced for the Fund’s investment in mortgage- and other asset-backed securities, the value of which may fluctuate more significantly in response to interest rate changes. When interest rates decrease, the Fund’s dividends may decline.

Prepayment and Extension Risk – When market interest rates decline, certain debt obligations held by the Fund may be repaid more quickly than anticipated, requiring the Fund to reinvest the proceeds of those repayments in obligations which bear a lower interest rate. Conversely, when market interest rates increase, certain debt obligations held by the Fund may be repaid more slowly than anticipated, causing assets of the Fund to remain invested in relatively lower yielding obligations. These risks may be more pronounced for the Fund’s investments in mortgage-backed and asset-backed securities.

Credit Risk – All securities owned by the Fund may be subject to default, delays in payment, adverse legislation or other government action, or could be downgraded by ratings agencies, reducing the value of the Fund’s shares. Securities backed by the full faith and credit of the U.S. government, such as U.S. Treasury obligations, are commonly regarded as having small exposure to credit risk. Obligations of certain U.S. government agencies, instrumentalities and government sponsored enterprises (sometimes referred to as “agency obligations”) are not direct obligations of the United States, may not be backed by the full faith and credit of the U.S. government, and may have a greater exposure to credit risk. Although the U.S. government is required by law to provide credit support for some agency obligations, there is no assurance that the U.S. government would provide financial support for any such obligation on a default by the issuing agency, instrumentality or enterprise in the absence of a legal requirement to do so. As of the date of this Prospectus, securities backed by the full faith and credit of the U.S. government, and securities of U.S. government agencies, instrumentalities and enterprises which may be purchased by the Fund, are rated “Aaa” by Moody’s Investors Services or “AA+” by S&P Global Ratings. Ratings agencies may reduce the ratings of any securities in the future. Lower-rated or unrated obligations in which the Fund is permitted to invest may have, or may be perceived to have, greater risk of default and ratings downgrades.

Market and Economic Risk – The value of the Fund’s investments may decline and its share value may be reduced due to changes in general economic and market conditions. For example, a fall in worldwide demand for U.S. government securities or general economic decline could lower the value of those securities.

Risks Affecting Specific Issuers – The value of a debt obligation may decline in response to developments affecting the specific issuer of the obligation, even if other issuers or the overall economy are unaffected. These developments may include

a variety of factors, including but not limited to management issues or other corporate disruption, a decline in revenues or profitability, an increase in costs, or an adverse effect on the issuer’s competitive position.

Foreign Investment Risk – Investments in the debt obligations of foreign issuers may involve risks including adverse fluctuations in currency exchange rates, political instability, confiscations, taxes or restrictions on currency exchange, difficulty in selling foreign investments, and reduced legal protection. These risks may be more pronounced for investments in developing countries. In addition, some foreign government debt obligations may be subject to default, delays in payment, adverse legislation or government action, or could be downgraded by ratings agencies.

Liquidity Risk – Due to a lack of demand in the marketplace or other factors, the Fund may not be able to sell promptly some or all of the obligations that it holds, or may only be able to sell obligations at less than desired prices.

Structured Products Risk – Investments in securities that are backed by, or represent interests in, an underlying pool of securities or other assets, including investments in mortgage- and asset-backed securities and in collateralized mortgage obligations and collateralized debt obligations, involve the risks associated with the underlying assets (e.g., the risk of default by mortgagors whose mortgages are included in a mortgage-backed security or collateralized mortgage obligation), and may also involve different or greater risks, including the risk that distributions from the underlying assets will be inadequate to make interest or other payments to the Fund, the risk that the issuer of the securities will fail to administer the underlying assets properly or become insolvent, and the risk that the securities will be less liquid than other Fund investments.

Cybersecurity and Operational Risk – Operational failures, cyber-attacks or other disruptions that affect the Fund’s service providers, the Fund’s counterparties, other market participants or the issuers of securities held by the Fund may adversely affect the Fund and its shareholders, including by causing losses for the Fund or impairing Fund operations.

Additional information about Fund investments, investment strategies, and risks of investing in the Fund appears below beginning on page 118 of the Prospectus.
Risk Lose Money [Text] rr_RiskLoseMoney Accordingly, the loss of money is a risk of investing in the Fund.
RIsk Not Insured [Text] rr_RiskNotInsured An investment in the Fund is not a deposit in any bank and is not insured or guaranteed by the Federal Deposit Insurance Corporation or any other government agency.
Bar Chart and Performance Table [Heading] rr_BarChartAndPerformanceTableHeading Past Performance of the Fund
Performance Narrative [Text Block] rr_PerformanceNarrativeTextBlock

The following information provides some indication of the risks of investing in Limited Term Income Fund by showing how the Fund’s investment results vary from year to year. The bar chart shows how the annual total returns for Class A shares have been different in each full year shown. The average annual total return figures compare Class A, Class C, Class C2 and Class I share performance to the Bloomberg Barclays Intermediate US Government/Credit Total Return Index Value Unhedged, a broad measure of market performance. Past performance (before and after taxes) is not necessarily an indication of how the Fund will perform in the future. The performance information shown is as of the calendar year ended December 31, 2021. Updated performance information may be obtained on the Thornburg website at Thornburg.com or by calling 1-800-847-0200.
Performance Information Illustrates Variability of Returns [Text] rr_PerformanceInformationIllustratesVariabilityOfReturns The following information provides some indication of the risks of investing in Limited Term Income Fund by showing how the Fund’s investment results vary from year to year.
Performance Availability Phone [Text] rr_PerformanceAvailabilityPhone 1-800-847-0200
Performance Availability Website Address [Text] rr_PerformanceAvailabilityWebSiteAddress Thornburg.com
Performance Past Does Not Indicate Future [Text] rr_PerformancePastDoesNotIndicateFuture Past performance (before and after taxes) is not necessarily an indication of how the Fund will perform in the future.
Bar Chart [Heading] rr_BarChartHeading Annual Total Returns – Class A Shares
Bar Chart Does Not Reflect Sales Loads [Text] rr_BarChartDoesNotReflectSalesLoads The sales charge for Class A shares is not reflected in the returns shown in the bar chart above and the returns would be less if the charge was taken into account.
Bar Chart Closing [Text Block] rr_BarChartClosingTextBlock

Total
Returns

Quarter
ended

Highest Quarterly Results

5.71%

6/30/2020

Lowest Quarterly Results

(2.06)%

6/30/2013

The sales charge for Class A shares is not reflected in the returns shown in the bar chart above and the returns would be less if the charge was taken into account.
Performance Table Heading rr_PerformanceTableHeading Average Annual Total Returns (periods ended 12-31-21)
Performance Table Uses Highest Federal Rate rr_PerformanceTableUsesHighestFederalRate After-tax returns are calculated using the highest historical individual federal marginal income tax rates, and do not reflect state or local income taxes.
Performance Table Not Relevant to Tax Deferred rr_PerformanceTableNotRelevantToTaxDeferred Actual after-tax returns depend on an investor’s own tax situation and may differ from the returns shown, and after-tax returns shown are not relevant to investors who hold their Fund shares through tax-deferred arrangements, such as 401(k) plans or individual retirement accounts.
Performance Table One Class of after Tax Shown [Text] rr_PerformanceTableOneClassOfAfterTaxShown The after-tax returns shown relate only to Class A shares, and after-tax returns for other share classes will vary.
Performance Table Closing [Text Block] rr_PerformanceTableClosingTextBlock

After-tax returns are calculated using the highest historical individual federal marginal income tax rates, and do not reflect state or local income taxes. Actual after-tax returns depend on an investor’s own tax situation and may differ from the returns shown, and after-tax returns shown are not relevant to investors who hold their Fund shares through tax-deferred arrangements, such as 401(k) plans or individual retirement accounts. The after-tax returns shown relate only to Class A shares, and after-tax returns for other share classes will vary.
Retail | Thornburg Limited Term Income Fund | Thornburg Limited Term Income Fund - Class A  
Prospectus [Line Items] rr_ProspectusLineItems  
Trading Symbol dei_TradingSymbol THIFX
Maximum Sales Charge Imposed on Purchases (as a percentage of Offering Price) rr_MaximumSalesChargeImposedOnPurchasesOverOfferingPrice 2.25%
Maximum Deferred Sales Charge (as a percentage) rr_MaximumDeferredSalesChargeOverOther none [34]
Management Fees (as a percentage of Assets) rr_ManagementFeesOverAssets 0.31%
Distribution and Service (12b-1) Fees rr_DistributionAndService12b1FeesOverAssets 0.25%
Other Expenses (as a percentage of Assets): rr_OtherExpensesOverAssets 0.21%
Expenses (as a percentage of Assets) rr_ExpensesOverAssets 0.77%
Fee Waiver or Reimbursement rr_FeeWaiverOrReimbursementOverAssets
Net Expenses (as a percentage of Assets) rr_NetExpensesOverAssets 0.77%
Expense Example, with Redemption, 1 Year rr_ExpenseExampleYear01 $ 302
Expense Example, with Redemption, 3 Years rr_ExpenseExampleYear03 465
Expense Example, with Redemption, 5 Years rr_ExpenseExampleYear05 643
Expense Example, with Redemption, 10 Years rr_ExpenseExampleYear10 $ 1,158
Annual Return 2012 rr_AnnualReturn2012 7.50%
Annual Return 2013 rr_AnnualReturn2013 (0.17%)
Annual Return 2014 rr_AnnualReturn2014 3.47%
Annual Return 2015 rr_AnnualReturn2015 0.47%
Annual Return 2016 rr_AnnualReturn2016 3.12%
Annual Return 2017 rr_AnnualReturn2017 2.27%
Annual Return 2018 rr_AnnualReturn2018 0.99%
Annual Return 2019 rr_AnnualReturn2019 5.37%
Annual Return 2020 rr_AnnualReturn2020 7.37%
Annual Return 2021 rr_AnnualReturn2021 (1.07%)
Highest Quarterly Return, Label rr_HighestQuarterlyReturnLabel Highest Quarterly Results
Highest Quarterly Return, Date rr_BarChartHighestQuarterlyReturnDate Jun. 30, 2020
Highest Quarterly Return rr_BarChartHighestQuarterlyReturn 5.71%
Lowest Quarterly Return, Label rr_LowestQuarterlyReturnLabel Lowest Quarterly Results
Lowest Quarterly Return, Date rr_BarChartLowestQuarterlyReturnDate Jun. 30, 2013
Lowest Quarterly Return rr_BarChartLowestQuarterlyReturn (2.06%)
1 Year rr_AverageAnnualReturnYear01 (3.28%)
5 Years rr_AverageAnnualReturnYear05 2.63%
10 Years rr_AverageAnnualReturnYear10 2.74%
Retail | Thornburg Limited Term Income Fund | Thornburg Limited Term Income Fund - Class A | After Taxes on Distributions  
Prospectus [Line Items] rr_ProspectusLineItems  
1 Year rr_AverageAnnualReturnYear01 (3.79%)
5 Years rr_AverageAnnualReturnYear05 1.66%
10 Years rr_AverageAnnualReturnYear10 1.71%
Retail | Thornburg Limited Term Income Fund | Thornburg Limited Term Income Fund - Class A | After Taxes on Distributions and Sales  
Prospectus [Line Items] rr_ProspectusLineItems  
1 Year rr_AverageAnnualReturnYear01 (1.94%)
5 Years rr_AverageAnnualReturnYear05 1.60%
10 Years rr_AverageAnnualReturnYear10 1.66%
Retail | Thornburg Limited Term Income Fund | Thornburg Limited Term Income Fund - Class A | Bloomberg Barclays Intermediate US Government/Credit Total Return Index Value Unhedged (reflects no deduction for fees, expenses, or taxes)  
Prospectus [Line Items] rr_ProspectusLineItems  
1 Year rr_AverageAnnualReturnYear01 (1.44%)
5 Years rr_AverageAnnualReturnYear05 2.91%
10 Years rr_AverageAnnualReturnYear10 2.38%
Retail | Thornburg Limited Term Income Fund | Thornburg Limited Term Income Fund - Class C  
Prospectus [Line Items] rr_ProspectusLineItems  
Trading Symbol dei_TradingSymbol THICX
Maximum Sales Charge Imposed on Purchases (as a percentage of Offering Price) rr_MaximumSalesChargeImposedOnPurchasesOverOfferingPrice none
Maximum Deferred Sales Charge (as a percentage) rr_MaximumDeferredSalesChargeOverOther 0.50% [35]
Management Fees (as a percentage of Assets) rr_ManagementFeesOverAssets 0.31%
Distribution and Service (12b-1) Fees rr_DistributionAndService12b1FeesOverAssets 0.50%
Other Expenses (as a percentage of Assets): rr_OtherExpensesOverAssets 0.18%
Expenses (as a percentage of Assets) rr_ExpensesOverAssets 0.99%
Fee Waiver or Reimbursement rr_FeeWaiverOrReimbursementOverAssets
Net Expenses (as a percentage of Assets) rr_NetExpensesOverAssets 0.99%
Expense Example, with Redemption, 1 Year rr_ExpenseExampleYear01 $ 151
Expense Example, with Redemption, 3 Years rr_ExpenseExampleYear03 315
Expense Example, with Redemption, 5 Years rr_ExpenseExampleYear05 547
Expense Example, with Redemption, 10 Years rr_ExpenseExampleYear10 1,213
Expense Example, No Redemption, 1 Year rr_ExpenseExampleNoRedemptionYear01 101
Expense Example, No Redemption, 3 Years rr_ExpenseExampleNoRedemptionYear03 315
Expense Example, No Redemption, 5 Years rr_ExpenseExampleNoRedemptionYear05 547
Expense Example, No Redemption, 10 Years rr_ExpenseExampleNoRedemptionYear10 $ 1,213
1 Year rr_AverageAnnualReturnYear01 (1.78%)
5 Years rr_AverageAnnualReturnYear05 2.73%
10 Years rr_AverageAnnualReturnYear10 2.66%
Retail | Thornburg Limited Term Income Fund | Thornburg Limited Term Income Fund - Class C | Bloomberg Barclays Intermediate US Government/Credit Total Return Index Value Unhedged (reflects no deduction for fees, expenses, or taxes)  
Prospectus [Line Items] rr_ProspectusLineItems  
1 Year rr_AverageAnnualReturnYear01 (1.44%)
5 Years rr_AverageAnnualReturnYear05 2.91%
10 Years rr_AverageAnnualReturnYear10 2.38%
Retail | Thornburg Limited Term Income Fund | Thornburg Limited Term Income Fund - Class C2  
Prospectus [Line Items] rr_ProspectusLineItems  
Trading Symbol dei_TradingSymbol THIQX
Maximum Sales Charge Imposed on Purchases (as a percentage of Offering Price) rr_MaximumSalesChargeImposedOnPurchasesOverOfferingPrice none
Maximum Deferred Sales Charge (as a percentage) rr_MaximumDeferredSalesChargeOverOther 0.65% [35]
Management Fees (as a percentage of Assets) rr_ManagementFeesOverAssets 0.31%
Distribution and Service (12b-1) Fees rr_DistributionAndService12b1FeesOverAssets 0.65%
Other Expenses (as a percentage of Assets): rr_OtherExpensesOverAssets 0.36%
Expenses (as a percentage of Assets) rr_ExpensesOverAssets 1.32%
Fee Waiver or Reimbursement rr_FeeWaiverOrReimbursementOverAssets (0.08%) [36]
Net Expenses (as a percentage of Assets) rr_NetExpensesOverAssets 1.24%
Expense Example, with Redemption, 1 Year rr_ExpenseExampleYear01 $ 191
Expense Example, with Redemption, 3 Years rr_ExpenseExampleYear03 410
Expense Example, with Redemption, 5 Years rr_ExpenseExampleYear05 716
Expense Example, with Redemption, 10 Years rr_ExpenseExampleYear10 1,583
Expense Example, No Redemption, 1 Year rr_ExpenseExampleNoRedemptionYear01 126
Expense Example, No Redemption, 3 Years rr_ExpenseExampleNoRedemptionYear03 410
Expense Example, No Redemption, 5 Years rr_ExpenseExampleNoRedemptionYear05 716
Expense Example, No Redemption, 10 Years rr_ExpenseExampleNoRedemptionYear10 $ 1,583
1 Year rr_AverageAnnualReturnYear01 (2.18%)
Since Inception rr_AverageAnnualReturnSinceInception (0.61%)
Inception Date rr_AverageAnnualReturnInceptionDate Oct. 01, 2020
Retail | Thornburg Limited Term Income Fund | Thornburg Limited Term Income Fund - Class C2 | Bloomberg Barclays Intermediate US Government/Credit Total Return Index Value Unhedged (reflects no deduction for fees, expenses, or taxes)  
Prospectus [Line Items] rr_ProspectusLineItems  
1 Year rr_AverageAnnualReturnYear01 (1.44%)
Since Inception rr_AverageAnnualReturnSinceInception (0.77%)
Retail | Thornburg Limited Term Income Fund | Thornburg Limited Term Income Fund - Class I  
Prospectus [Line Items] rr_ProspectusLineItems  
Trading Symbol dei_TradingSymbol THIIX
Maximum Sales Charge Imposed on Purchases (as a percentage of Offering Price) rr_MaximumSalesChargeImposedOnPurchasesOverOfferingPrice none
Maximum Deferred Sales Charge (as a percentage) rr_MaximumDeferredSalesChargeOverOther none
Management Fees (as a percentage of Assets) rr_ManagementFeesOverAssets 0.31%
Distribution and Service (12b-1) Fees rr_DistributionAndService12b1FeesOverAssets none
Other Expenses (as a percentage of Assets): rr_OtherExpensesOverAssets 0.19%
Expenses (as a percentage of Assets) rr_ExpensesOverAssets 0.50%
Fee Waiver or Reimbursement rr_FeeWaiverOrReimbursementOverAssets (0.01%) [36]
Net Expenses (as a percentage of Assets) rr_NetExpensesOverAssets 0.49%
Expense Example, with Redemption, 1 Year rr_ExpenseExampleYear01 $ 50
Expense Example, with Redemption, 3 Years rr_ExpenseExampleYear03 159
Expense Example, with Redemption, 5 Years rr_ExpenseExampleYear05 279
Expense Example, with Redemption, 10 Years rr_ExpenseExampleYear10 $ 627
1 Year rr_AverageAnnualReturnYear01 (0.80%)
5 Years rr_AverageAnnualReturnYear05 3.25%
10 Years rr_AverageAnnualReturnYear10 3.23%
Retail | Thornburg Limited Term Income Fund | Thornburg Limited Term Income Fund - Class I | Bloomberg Barclays Intermediate US Government/Credit Total Return Index Value Unhedged (reflects no deduction for fees, expenses, or taxes)  
Prospectus [Line Items] rr_ProspectusLineItems  
1 Year rr_AverageAnnualReturnYear01 (1.44%)
5 Years rr_AverageAnnualReturnYear05 2.91%
10 Years rr_AverageAnnualReturnYear10 2.38%
Retail | Thornburg Ultra Short Income Fund  
Prospectus [Line Items] rr_ProspectusLineItems  
Risk/Return [Heading] rr_RiskReturnHeading Ultra Short Income Fund
Objective [Heading] rr_ObjectiveHeading Investment Goal
Objective, Primary [Text Block] rr_ObjectivePrimaryTextBlock

The Fund seeks current income, consistent with preservation of capital.

Expense [Heading] rr_ExpenseHeading Fees and Expenses of the Fund
Expense Narrative [Text Block] rr_ExpenseNarrativeTextBlock

This table describes the fees and expenses that you may pay if you buy and hold shares of the Fund. You may qualify for discounts from the sales charges applicable to Class A shares if you or other qualifying account holders invest, or agree to invest in the future, at least $50,000 in the Thornburg Funds. More information about this and other discounts and sales charge waivers is available from your financial intermediary, in the Prospectus under the captions “Class A Sales Charge Waivers,” beginning on page 146, and “Appendix A – Sales Charge Waivers Offered by Financial Intermediaries,” beginning on page 200, and in the Statement of Additional Information under the caption “Additional Information Respecting Purchase and Redemption of Shares,” beginning on page 108.
Shareholder Fees Caption [Text] rr_ShareholderFeesCaption Shareholder Fees (fees paid directly from your investment)
Operating Expenses Caption [Text] rr_OperatingExpensesCaption Annual Fund Operating Expenses (expenses that you pay each year as a percentage of the value of your investment)
Fee Waiver or Reimbursement over Assets, Date of Termination rr_FeeWaiverOrReimbursementOverAssetsDateOfTermination February 1, 2023
Portfolio Turnover [Heading] rr_PortfolioTurnoverHeading Portfolio Turnover.
Portfolio Turnover [Text Block] rr_PortfolioTurnoverTextBlock

The Fund pays transaction costs, such as commissions, when it buys and sells securities (or “turns over”) its portfolio. A higher portfolio turnover rate may indicate higher transaction costs and may result in higher taxes when Fund shares are held in a taxable account. These costs, which are not reflected in Annual Fund Operating Expenses or in the Example, affect the Fund’s performance. During the most recent fiscal year, the Fund’s portfolio turnover rate was 37.51% of the average value of its portfolio.
Portfolio Turnover, Rate rr_PortfolioTurnoverRate 37.51%
Expense Breakpoint Discounts [Text] rr_ExpenseBreakpointDiscounts You may qualify for discounts from the sales charges applicable to Class A shares if you or other qualifying account holders invest, or agree to invest in the future, at least $50,000 in the Thornburg Funds.
Expense Breakpoint, Minimum Investment Required [Amount] rr_ExpenseBreakpointMinimumInvestmentRequiredAmount $ 50,000
Expense Example [Heading] rr_ExpenseExampleHeading Example.
Expense Example Narrative [Text Block] rr_ExpenseExampleNarrativeTextBlock

This Example is intended to help you compare the cost of investing in the Fund with the cost of investing in other mutual funds.

The Example assumes that you invest $10,000 in the Fund for the time periods indicated and then redeem all of your shares at the end of those periods. The Example also assumes that your investment has a 5% return each year, dividends and distributions are reinvested, and that the Fund’s operating expenses remain the same. Although your actual costs may be higher or lower, based on these assumptions (and giving effect to fee waivers and expense reimbursements in the first year) your costs would be:
Strategy [Heading] rr_StrategyHeading Principal Investment Strategies
Strategy Narrative [Text Block] rr_StrategyNarrativeTextBlock

Thornburg Investment Management Inc. (“Thornburg”) actively manages the Fund’s holdings in pursuing the Fund’s investment goal. While Thornburg follows domestic and international economic developments, outlooks for securities markets, interest rates and inflation, the supply and demand for debt obligations, and other factors, the Fund’s investments are determined by individual security analysis. The Fund ordinarily acquires and holds securities for investment rather than for realization of gains by short-term trading on market fluctuations. However, it may dispose of any security prior to its scheduled maturity to enhance income or reduce loss, to change the portfolio’s average duration or average maturity, or to otherwise respond to current market conditions.

Under normal conditions, the Fund invests at least 80% of its net assets in (i) obligations of the U.S. government, its agencies and instrumentalities, and (ii) debt obligations rated at the time of purchase in one of the four highest ratings of S&P Global Ratings (AAA, AA, A, or BBB) or Moody’s Investors Services, Inc. (Aaa, Aa, A, or Baa) or, if no credit rating is available, judged to be of comparable quality by Thornburg. The Fund may purchase corporate debt, municipal securities, and short-term commercial paper and bankers’ acceptances, and the Fund may also purchase securities backed by an underlying pool of debt obligations, including mortgage-backed securities, asset-backed securities, collateralized mortgage obligations, and collateralized debt obligations (sometimes referred to collectively as “structured products”). The Fund may purchase foreign securities of the same types and quality as the domestic securities it purchases when Thornburg anticipates foreign securities offer more investment potential. The Fund may invest in debt obligations which are rated by S&P Global Ratings or Moody’s Investors Services, Inc. at the time of purchase as below investment grade (commonly referred to as “junk” or “high yield” bonds) or, if no credit rating is available, are judged to be of comparable quality by Thornburg, but such investments will be less than 20% of the Fund’s net assets under normal conditions.

The Fund may also purchase or sell futures contracts or purchase or sell interest rate swaps or credit default swaps to hedge against a decline in the value of the Fund’s other investments or to manage portfolio duration.

Because the magnitude of changes in the value of interest-bearing obligations is greater for obligations with longer durations given an equivalent change in interest rates, the Fund seeks to reduce changes in its share value compared to longer duration fixed income portfolios by maintaining a portfolio of investments with a dollar-weighted average duration of normally no more than one half (0.5) of a year. Duration is a measure of estimated sensitivity to interest rate changes, and a debt obligation or a portfolio of obligations with a higher duration will typically be more sensitive to interest rate changes than an obligation or a portfolio with a lower duration. Duration is commonly expressed as a number, which is the expected percentage change in an obligation’s price upon a 1% change in interest rates. For example, an obligation with a duration of 0.5 would be expected to change in price by approximately 0.5% in response to a 1% change in interest rates. There is no limitation on the duration or maturity of any specific security the Fund may purchase, and the Fund may sell any security before it matures. The Fund also attempts to reduce changes in share value through credit analysis, selection, and diversification.

The Fund ordinarily acquires and holds securities for investment rather than for realization of gains by short-term trading on market fluctuations. However, it may sell an investment prior to its scheduled maturity date to enhance income or reduce loss, to change the portfolio’s average duration or average maturity, to pursue other investment opportunities, in response to changes in the conditions or business of the investment’s issuer or changes in overall market conditions, or if, in Thornburg’s opinion, the investment no longer serves to achieve the Fund’s investment goals.  The objective of preserving capital may prevent the Fund from obtaining the highest yields available.
Risk [Heading] rr_RiskHeading Principal Investment Risks
Risk Narrative [Text Block] rr_RiskNarrativeTextBlock

Although the Fund may acquire obligations issued or guaranteed by the U.S. government and its agencies, instrumentalities and enterprises, neither the Fund’s net asset value nor its dividends are guaranteed by the U.S. government. An investment in the Fund is not a deposit in any bank and is not insured or guaranteed by the Federal Deposit Insurance Corporation or any other government agency. Accordingly, the loss of money is a risk of investing in the Fund. The value of the Fund’s shares and its dividends may fluctuate from day to day and over time, and when you sell your shares they may be worth less than what you paid for them. The Fund seeks higher income than is typically available, across market cycles, from investment in a money market fund. Consequently, if your sole objective is preservation of capital, then the Fund may not be suitable for you because the Fund’s share value will fluctuate, including as interest rates change. Investors whose sole objective is preservation of capital may wish to consider a high quality money market fund. The following is a summary of the principal risks of investing in the Fund.

Management Risk – The Fund is an actively managed portfolio, and the value of the Fund may be reduced if Thornburg pursues unsuccessful investments or fails to correctly identify risks affecting the broad economy or specific issuers in which the Fund invests.

Interest Rate Risk – When interest rates increase, the value of the Fund’s investments may decline and the Fund’s share value may be reduced. This effect is typically more pronounced for intermediate and longer-term obligations. When interest rates decrease, the Fund’s dividends may decline.

Prepayment and Extension Risk – When market interest rates decline, certain debt obligations held by the Fund may be repaid more quickly than anticipated, requiring the Fund to reinvest the proceeds of those repayments in obligations which bear a lower interest rate. Conversely, when market interest rates increase, certain debt obligations held by the Fund may be repaid more slowly than anticipated, causing assets of the Fund to remain invested in relatively lower yielding obligations. These risks may be more pronounced for the Fund’s investments in mortgage-backed and asset-backed securities.

Credit Risk – All securities owned by the Fund may be subject to default, delays in payment, adverse legislation or other government action, or could be downgraded by ratings agencies, reducing the value of the Fund’s shares. Securities backed by the full faith and credit of the U.S. government, such as U.S. Treasury obligations, are commonly regarded as having small exposure to credit risk. Obligations of certain U.S. government agencies, instrumentalities and government sponsored enterprises (sometimes referred to as “agency obligations”) are not direct obligations of the United States, may not be backed by the full faith and credit of the U.S. government, and may have a greater exposure to credit risk. Although the U.S. government is required by law to provide credit support for some agency obligations, there is no assurance that the U.S. government would provide financial support for any such obligation on a default by the issuing agency, instrumentality or enterprise in the absence of a legal requirement to do so. As of the date of this Prospectus, securities backed by the U.S. government, and the securities of U.S. government agencies, instrumentalities and enterprises that may be purchased by the Fund are rated “Aaa” by Moody’s Investors Services or “AA+” by S&P Global Ratings. Ratings agencies may reduce the ratings of any securities in the future.

High Yield Risk – Debt obligations that are rated below investment grade and unrated obligations of similar credit quality (commonly referred to as “junk” or “high yield” bonds) may have a substantial risk of loss. These obligations are generally considered to be speculative with respect to the issuer’s ability to pay interest and principal when due. These obligations may be subject to greater price volatility than investment grade obligations, and their prices may decline significantly in periods of general economic difficulty or in response to adverse publicity, changes in investor perceptions or other factors. These obligations may also be subject to greater liquidity risk.

Market and Economic Risk – The value of the Fund’s investments may decline and its share value may be reduced due to changes in general economic and market conditions. For example, a fall in worldwide demand for U.S. government securities or general economic decline could lower the value of those securities.

Risks Affecting Specific Issuers – The value of a debt obligation may decline in response to developments affecting the specific issuer of the obligation, even if other issuers or the overall economy are unaffected. These developments may include a variety of factors, including but not limited to management issues or other corporate disruption, a decline in revenues or profitability, an increase in costs, or an adverse effect on the issuer’s competitive position.

Foreign Investment Risk – Investments in the debt obligations of foreign issuers may involve risks including adverse fluctuations in currency exchange rates, political instability, confiscations, taxes, or restrictions on currency exchange, difficulty in selling foreign investments, and reduced legal protection. These risks may be more pronounced for investments in developing countries. In addition, some foreign government debt obligations may be subject to default, delays in payment, adverse legislation or government action, or could be downgraded by ratings agencies.

Liquidity Risk – Due to lack of demand in the marketplace or other factors, the Fund may not be able to sell promptly some or all of the obligations that it holds, or may only be able to sell obligations at less than desired prices.

Structured Products Risk – Investments in securities that are backed by, or represent interests in, an underlying pool of securities or other assets, including investments in mortgage- and asset-backed securities and in collateralized mortgage obligations and collateralized debt obligations, involve the risks associated with the underlying assets (e.g., the risk of default by mortgagors whose mortgages are included in a mortgage-backed security or collateralized mortgage obligation), and may also involve the risk that distributions from the underlying assets will be inadequate to make interest or other payments to the Fund, the risk that the issuer of the securities will fail to administer the underlying assets properly or become insolvent, and the risk that the securities will be less liquid than other Fund investments.

Derivatives Risk – The Fund’s investments in futures, interest rate swaps, and credit default swaps involve the risks associated with the securities or other assets underlying those derivatives, including the risk of changes in the value of the underlying assets between the date that the Fund enters into the derivatives transaction and the date that the Fund closes out that transaction. The Fund’s investments in futures, interest rate swaps, and credit default swaps also involve the risk that the other party to the transaction will be unable or unwilling to perform its obligations to the Fund, that the Fund will be unable to sell or close its positions in such derivatives or will be delayed in doing so, and that the Fund will have difficulty valuing such derivatives.

Cybersecurity and Operational Risk – Operational failures, cyber-attacks or other disruptions that affect the Fund’s service providers, the Fund’s counterparties, other market participants or the issuers of securities held by the Fund may adversely affect the Fund and its shareholders, including by causing losses for the Fund or impairing Fund operations.

Additional information about Fund investments, investment strategies and risks of investing in the Fund appears beginning on page 118 of the Prospectus.
Risk Lose Money [Text] rr_RiskLoseMoney Accordingly, the loss of money is a risk of investing in the Fund.
RIsk Not Insured [Text] rr_RiskNotInsured An investment in the Fund is not a deposit in any bank and is not insured or guaranteed by the Federal Deposit Insurance Corporation or any other government agency.
Bar Chart and Performance Table [Heading] rr_BarChartAndPerformanceTableHeading Past Performance of the Fund
Performance Narrative [Text Block] rr_PerformanceNarrativeTextBlock

The following information provides some indication of the risks of investing in Ultra Short Income Fund by showing how the Fund’s investment results vary from year to year. The bar chart shows how the annual total returns for Class A shares have been different in each full year shown. The average annual total return figures compare Class A and Class I share performance to the ICE BofAML U.S. Treasury Bill Index, a broad measure of market performance. Past performance (before and after taxes) is not necessarily an indication of how the Fund will perform in the future. The performance information shown is as of the calendar year ended December 31, 2021. Updated performance information may be obtained on the Thornburg website at Thornburg.com or by calling 1-800-847-0200.
Performance Information Illustrates Variability of Returns [Text] rr_PerformanceInformationIllustratesVariabilityOfReturns The following information provides some indication of the risks of investing in Ultra Short Income Fund by showing how the Fund’s investment results vary from year to year.
Performance Availability Phone [Text] rr_PerformanceAvailabilityPhone 1-800-847-0200
Performance Availability Website Address [Text] rr_PerformanceAvailabilityWebSiteAddress Thornburg.com
Performance Past Does Not Indicate Future [Text] rr_PerformancePastDoesNotIndicateFuture Past performance (before and after taxes) is not necessarily an indication of how the Fund will perform in the future.
Bar Chart [Heading] rr_BarChartHeading Annual Total Returns – Class A Shares
Bar Chart Does Not Reflect Sales Loads [Text] rr_BarChartDoesNotReflectSalesLoads The sales charge for Class A shares is not reflected in the returns shown in the bar chart above, and the returns would be less if the charge was taken into account.
Bar Chart Closing [Text Block] rr_BarChartClosingTextBlock

Total
Returns

Quarter
ended

Highest Quarterly Results

3.80%

6/30/2020

Lowest Quarterly Results

(1.66)%

3/31/2020

The sales charge for Class A shares is not reflected in the returns shown in the bar chart above, and the returns would be less if the charge was taken into account.
Performance Table Heading rr_PerformanceTableHeading Average Annual Total Returns (periods ended 12-31-21)
Performance Table Uses Highest Federal Rate rr_PerformanceTableUsesHighestFederalRate After-tax returns are calculated using the highest historical individual federal marginal income tax rates, and do not reflect state or local income taxes.
Performance Table Not Relevant to Tax Deferred rr_PerformanceTableNotRelevantToTaxDeferred Actual after-tax returns depend on an investor’s own tax situation, and may differ from the returns shown, and after-tax returns shown are not relevant to investors who hold their Fund shares through tax-deferred arrangements, such as 401(k) plans or individual retirement accounts.
Performance Table One Class of after Tax Shown [Text] rr_PerformanceTableOneClassOfAfterTaxShown The after-tax returns shown relate only to Class A shares, and after-tax returns for other share classes will vary.
Performance Table Closing [Text Block] rr_PerformanceTableClosingTextBlock

After-tax returns are calculated using the highest historical individual federal marginal income tax rates, and do not reflect state or local income taxes. Actual after-tax returns depend on an investor’s own tax situation, and may differ from the returns shown, and after-tax returns shown are not relevant to investors who hold their Fund shares through tax-deferred arrangements, such as 401(k) plans or individual retirement accounts. The after-tax returns shown relate only to Class A shares, and after-tax returns for other share classes will vary.
Retail | Thornburg Ultra Short Income Fund | Thornburg Ultra Short Income Fund Class A  
Prospectus [Line Items] rr_ProspectusLineItems  
Trading Symbol dei_TradingSymbol TLDAX
Maximum Sales Charge Imposed on Purchases (as a percentage of Offering Price) rr_MaximumSalesChargeImposedOnPurchasesOverOfferingPrice 2.25%
Maximum Deferred Sales Charge (as a percentage) rr_MaximumDeferredSalesChargeOverOther none [37]
Management Fees (as a percentage of Assets) rr_ManagementFeesOverAssets 0.25%
Distribution and Service (12b-1) Fees rr_DistributionAndService12b1FeesOverAssets 0.20%
Other Expenses (as a percentage of Assets): rr_OtherExpensesOverAssets 0.93%
Expenses (as a percentage of Assets) rr_ExpensesOverAssets 1.38%
Fee Waiver or Reimbursement rr_FeeWaiverOrReimbursementOverAssets (0.88%) [38]
Net Expenses (as a percentage of Assets) rr_NetExpensesOverAssets 0.50%
Expense Example, with Redemption, 1 Year rr_ExpenseExampleYear01 $ 275
Expense Example, with Redemption, 3 Years rr_ExpenseExampleYear03 567
Expense Example, with Redemption, 5 Years rr_ExpenseExampleYear05 881
Expense Example, with Redemption, 10 Years rr_ExpenseExampleYear10 $ 1,770
Annual Return 2014 rr_AnnualReturn2014 1.34%
Annual Return 2015 rr_AnnualReturn2015 0.28%
Annual Return 2016 rr_AnnualReturn2016 1.69%
Annual Return 2017 rr_AnnualReturn2017 1.31%
Annual Return 2018 rr_AnnualReturn2018 1.41%
Annual Return 2019 rr_AnnualReturn2019 3.74%
Annual Return 2020 rr_AnnualReturn2020 3.05%
Annual Return 2021 rr_AnnualReturn2021 0.12%
Highest Quarterly Return, Label rr_HighestQuarterlyReturnLabel Highest Quarterly Results
Highest Quarterly Return, Date rr_BarChartHighestQuarterlyReturnDate Jun. 30, 2020
Highest Quarterly Return rr_BarChartHighestQuarterlyReturn 3.80%
Lowest Quarterly Return, Label rr_LowestQuarterlyReturnLabel Lowest Quarterly Results
Lowest Quarterly Return, Date rr_BarChartLowestQuarterlyReturnDate Mar. 31, 2020
Lowest Quarterly Return rr_BarChartLowestQuarterlyReturn (1.66%)
1 Year rr_AverageAnnualReturnYear01 (2.14%)
5 Years rr_AverageAnnualReturnYear05 1.61%
Since Inception rr_AverageAnnualReturnSinceInception 1.42%
Inception Date rr_AverageAnnualReturnInceptionDate Dec. 30, 2013
Retail | Thornburg Ultra Short Income Fund | Thornburg Ultra Short Income Fund Class A | After Taxes on Distributions  
Prospectus [Line Items] rr_ProspectusLineItems  
1 Year rr_AverageAnnualReturnYear01 (2.67%)
5 Years rr_AverageAnnualReturnYear05 0.82%
Since Inception rr_AverageAnnualReturnSinceInception 0.78%
Retail | Thornburg Ultra Short Income Fund | Thornburg Ultra Short Income Fund Class A | After Taxes on Distributions and Sales  
Prospectus [Line Items] rr_ProspectusLineItems  
1 Year rr_AverageAnnualReturnYear01 (1.27%)
5 Years rr_AverageAnnualReturnYear05 0.89%
Since Inception rr_AverageAnnualReturnSinceInception 0.81%
Retail | Thornburg Ultra Short Income Fund | Thornburg Ultra Short Income Fund Class A | ICE BofAML US Treasury Bill Index (reflects no deduction for fees, expenses, or taxes)  
Prospectus [Line Items] rr_ProspectusLineItems  
1 Year rr_AverageAnnualReturnYear01 0.05%
5 Years rr_AverageAnnualReturnYear05 1.16%
Since Inception rr_AverageAnnualReturnSinceInception 0.79%
Retail | Thornburg Ultra Short Income Fund | Thornburg Ultra Short Income Fund Class I  
Prospectus [Line Items] rr_ProspectusLineItems  
Trading Symbol dei_TradingSymbol TLDIX
Maximum Sales Charge Imposed on Purchases (as a percentage of Offering Price) rr_MaximumSalesChargeImposedOnPurchasesOverOfferingPrice none
Maximum Deferred Sales Charge (as a percentage) rr_MaximumDeferredSalesChargeOverOther none
Management Fees (as a percentage of Assets) rr_ManagementFeesOverAssets 0.25%
Distribution and Service (12b-1) Fees rr_DistributionAndService12b1FeesOverAssets none
Other Expenses (as a percentage of Assets): rr_OtherExpensesOverAssets 0.51%
Expenses (as a percentage of Assets) rr_ExpensesOverAssets 0.76%
Fee Waiver or Reimbursement rr_FeeWaiverOrReimbursementOverAssets (0.46%) [38]
Net Expenses (as a percentage of Assets) rr_NetExpensesOverAssets 0.30%
Expense Example, with Redemption, 1 Year rr_ExpenseExampleYear01 $ 31
Expense Example, with Redemption, 3 Years rr_ExpenseExampleYear03 197
Expense Example, with Redemption, 5 Years rr_ExpenseExampleYear05 377
Expense Example, with Redemption, 10 Years rr_ExpenseExampleYear10 $ 899
1 Year rr_AverageAnnualReturnYear01 0.32%
5 Years rr_AverageAnnualReturnYear05 2.09%
Since Inception rr_AverageAnnualReturnSinceInception 1.80%
Inception Date rr_AverageAnnualReturnInceptionDate Dec. 30, 2013
Retail | Thornburg Ultra Short Income Fund | Thornburg Ultra Short Income Fund Class I | ICE BofAML US Treasury Bill Index (reflects no deduction for fees, expenses, or taxes)  
Prospectus [Line Items] rr_ProspectusLineItems  
1 Year rr_AverageAnnualReturnYear01 0.05%
5 Years rr_AverageAnnualReturnYear05 1.16%
Since Inception rr_AverageAnnualReturnSinceInception 0.79%
Retail | Thornburg Strategic Income Fund  
Prospectus [Line Items] rr_ProspectusLineItems  
Risk/Return [Heading] rr_RiskReturnHeading Strategic Income Fund
Objective [Heading] rr_ObjectiveHeading Investment Goal
Objective, Primary [Text Block] rr_ObjectivePrimaryTextBlock

The Fund’s primary investment goal is to seek a high level of current income.
Objective, Secondary [Text Block] rr_ObjectiveSecondaryTextBlock

The Fund’s secondary investment goal is some long-term capital appreciation.
Expense [Heading] rr_ExpenseHeading Fees and Expenses of the Fund
Expense Narrative [Text Block] rr_ExpenseNarrativeTextBlock

This table describes the fees and expenses that you may pay if you buy and hold shares of the Fund. You may qualify for discounts from the sales charges applicable to Class A shares if you or other qualifying account holders invest, or agree to invest in the future, at least $50,000 in the Thornburg Funds. More information about this and other discounts and sales charge waivers is available from your financial intermediary, in the Prospectus under the captions “Class A Sales Charge Waivers,” beginning on page 146, and “Appendix A – Sales Charge Waivers Offered by Financial Intermediaries,” beginning on page 200, and in the Statement of Additional Information under the caption “Additional Information Respecting Purchase and Redemption of Shares,” beginning on page 108.
Shareholder Fees Caption [Text] rr_ShareholderFeesCaption Shareholder Fees (fees paid directly from your investment)
Operating Expenses Caption [Text] rr_OperatingExpensesCaption Annual Fund Operating Expenses (expenses that you pay each year as a percentage of the value of your investment)
Fee Waiver or Reimbursement over Assets, Date of Termination rr_FeeWaiverOrReimbursementOverAssetsDateOfTermination February 1, 2023
Portfolio Turnover [Heading] rr_PortfolioTurnoverHeading Portfolio Turnover.
Portfolio Turnover [Text Block] rr_PortfolioTurnoverTextBlock

The Fund pays transaction costs, such as commissions, when it buys and sells securities (or “turns over”) its portfolio. A higher portfolio turnover rate may indicate higher transaction costs and may result in higher taxes when Fund shares are held in a taxable account. These costs, which are not reflected in Annual Fund Operating Expenses or in the Example, affect the Fund’s performance. During the most recent fiscal year, the Fund’s portfolio turnover rate was 28.55% of the average value of its portfolio.
Portfolio Turnover, Rate rr_PortfolioTurnoverRate 28.55%
Expense Breakpoint Discounts [Text] rr_ExpenseBreakpointDiscounts You may qualify for discounts from the sales charges applicable to Class A shares if you or other qualifying account holders invest, or agree to invest in the future, at least $50,000 in the Thornburg Funds.
Expense Breakpoint, Minimum Investment Required [Amount] rr_ExpenseBreakpointMinimumInvestmentRequiredAmount $ 50,000
Expense Example [Heading] rr_ExpenseExampleHeading Example.
Expense Example Narrative [Text Block] rr_ExpenseExampleNarrativeTextBlock

This Example is intended to help you compare the cost of investing in the Fund with the cost of investing in other mutual funds.

The Example assumes that you invest $10,000 in the Fund for the time periods indicated and then redeem all of your shares at the end of those periods. The Example also assumes that your investment has a 5% return each year, dividends and distributions are reinvested, and that the Fund’s operating expenses remain the same. Although your actual costs may be higher or lower, based on these assumptions (and giving effect to fee waivers and expense reimbursements in the first year), your costs would be:
Expense Example, No Redemption Narrative [Text Block] rr_ExpenseExampleNoRedemptionNarrativeTextBlock

You would pay the following expenses if you did not redeem your Class C shares:
Strategy [Heading] rr_StrategyHeading Principal Investment Strategies
Strategy Narrative [Text Block] rr_StrategyNarrativeTextBlock

The Fund pursues its investment goals by investing in a broad range of income-producing investments from throughout the world, primarily including debt obligations. The Fund expects, under normal conditions, to invest a majority of its assets in the debt obligations described below.

The Fund may invest in debt obligations of any kind, of any quality, and of any maturity. The Fund expects, under normal conditions, to select a majority of its investments from among the following types of debt obligations:

•bonds and other debt obligations issued by domestic and foreign companies of any size (including lower-rated “high yield” or “junk” bonds)

•mortgage-backed securities and other asset-backed securities, including commercial mortgage-backed securities

•convertible debt obligations

•obligations issued by foreign governments (including developing countries)

•collateralized mortgage obligations (“CMOs”), collateralized debt obligations (“CDOs”), collateralized bond obligations (“CBOs”), and collateralized loan obligations (“CLOs”)

•obligations of the U.S. government and its agencies and sponsored enterprises

•structured notes

•zero coupon bonds and “stripped” securities

•taxable municipal obligations and participations in municipal obligations

The Fund’s investments are determined by individual issuer and industry analysis. Investment decisions are based on domestic and international economic developments, outlooks for securities markets, interest rates and inflation, the supply and demand for debt securities, and analysis of specific issuers.

The Fund ordinarily acquires and holds securities for investment rather than for realization of gains by short-term trading on market fluctuations. However, it may sell an investment prior to its scheduled maturity date to enhance income or reduce loss, to change the portfolio’s average duration or average maturity, to pursue other investment opportunities, in response to changes in the conditions or business of the investment’s issuer or changes in overall market conditions, or if, in Thornburg’s opinion, the investment no longer serves to achieve the Fund’s investment goals.  The objective of preserving capital may prevent the Fund from obtaining the highest yields available.
Risk [Heading] rr_RiskHeading Principal Investment Risks
Risk Narrative [Text Block] rr_RiskNarrativeTextBlock

An investment in the Fund is not a deposit in any bank and is not insured or guaranteed by the Federal Deposit Insurance Corporation or any other government agency. Accordingly, the loss of money is a risk of investing in the Fund. The value of the Fund’s shares and its dividends may fluctuate from day to day and over time, and when you sell your shares they may be worth less than what you paid for them. The following is a summary of the principal risks of investing in the Fund. Please note that because the Fund’s objective is to provide high current income, the Fund invests with an emphasis on income, rather than stability of net asset value.

Management Risk – The Fund is an actively managed portfolio, and the value of the Fund may be reduced if Thornburg pursues unsuccessful investments or fails to correctly identify risks affecting the broad economy or specific issuers in which the Fund invests.

Interest Rate Risk – When interest rates increase, the value of the Fund’s investments may decline and the Fund’s share value may be reduced. This effect is typically more pronounced for intermediate and longer-term obligations. This effect is also typically more pronounced for mortgage- and other asset-backed securities, the value of which may fluctuate more significantly in response to interest rate changes. When interest rates decrease, the Fund’s dividends may decline.

Prepayment and Extension Risk – When market interest rates decline, certain debt obligations held by the Fund may be repaid more quickly than anticipated, requiring the Fund to reinvest the proceeds of those repayments in obligations which bear a lower interest rate. Conversely, when market interest rates increase, certain debt obligations held by the Fund may be repaid more slowly than anticipated, causing assets of the Fund to remain invested in relatively lower yielding obligations. These risks may be more pronounced for the Fund’s investments in mortgage-backed and asset-backed securities.

Credit Risk – If obligations held by the Fund are downgraded by ratings agencies or go into default, or if management action, legislation or other government action reduces the ability of issuers to pay principal and interest when due, the value of those obligations may decline and the Fund’s share value and the dividends paid by the Fund may be reduced. Because the ability of an issuer of a lower-rated or unrated obligation to pay principal and interest when due is typically less certain than for an issuer of a higher-rated obligation, lower-rated and unrated obligations are generally more vulnerable than higher-rated obligations to default, to ratings downgrades, and to liquidity risk. Debt obligations backed by so-called “subprime” mortgages may also be subject to a greater risk of default or downgrade. Debt obligations issued by the U.S. government or its agencies, instrumentalities and government sponsored enterprises are also subject to credit risk. Securities backed by the full faith and credit of the U.S. government, such as U.S. Treasury obligations, are commonly regarded as having small exposure to credit risk. Obligations of certain U.S. agencies, instrumentalities and enterprises (sometimes referred to as “agency obligations”) are not direct obligations of the U.S. government, may not be backed by the full faith and credit of the U.S. government, and may have a greater exposure to credit risk.

High Yield Risk – Debt obligations that are rated below investment grade and unrated obligations of similar credit quality (commonly referred to as “junk” or “high yield” bonds) may have a substantial risk of loss. These obligations are generally considered to be speculative with respect to the issuer’s ability to pay interest and principal when due. These obligations may be subject to greater price volatility than investment grade obligations, and their prices may decline significantly in periods of general economic difficulty or in response to adverse publicity, changes in investor perceptions or other factors. These obligations may also be subject to greater liquidity risk.

Market and Economic Risk – The value of the Fund’s investments may decline and its share value may be reduced due to changes in general economic and market conditions. This effect is typically more pronounced for lower-rated and unrated debt obligations (including particularly “junk” or “high yield” bonds), the value of which may fluctuate more significantly in response to poor economic growth or other changes in market conditions, political, economic and legal developments. The market value of any zero coupon bonds or “stripped” securities that the Fund may purchase will typically be more volatile than the value of a comparable, interest-paying bond. Additionally, zero coupon bonds and “stripped” securities are subject to the risk that the Fund may have to recognize income on its investment and make distributions to shareholders before it has received any cash payments on its investment.

Risks Affecting Specific Issuers – The value of a debt obligation may decline in response to developments affecting the specific issuer of the obligation or security, even if the overall industry or economy is unaffected. These developments may include a variety of factors, including but not limited to management issues or other corporate disruption, a decline in revenues or profitability, an increase in costs, or an adverse effect on the issuer’s competitive position.

Liquidity Risk – Due to a lack of demand in the marketplace or other factors, the Fund may not be able to sell some or all of its investments promptly, or may only be able to sell investments at less than desired prices. The market for lower-rated and unrated debt obligations (including particularly “junk” or “high yield” bonds) and debt obligations backed by so-called “subprime” mortgages may be less liquid than the market for other obligations, making it difficult for the Fund to value its investment in a lower-rated or unrated obligation or to sell the investment in a timely manner or at an acceptable price.

Small and Mid-Cap Company Risk – Investments in small-capitalization companies and mid-capitalization companies may involve additional risks, which may be relatively higher with smaller companies. These additional risks may result from limited product lines, more limited access to markets and financial resources, greater vulnerability to competition and changes in markets, lack of management depth, increased volatility in share price, and possible difficulties in valuing or selling these investments.

Foreign Investment Risk – Investments in the debt obligations of foreign issuers may involve risks including adverse fluctuations in currency exchange rates, political instability, confiscations, taxes or restrictions on currency exchange, difficulty in selling foreign investments, and reduced legal protection. In addition, some foreign government debt obligations may be subject to default, delays in payment, adverse legislation or government action, or could be downgraded by ratings agencies.

Developing Country Risk – The risks which may affect investments in foreign issuers (see “Foreign Investment Risk,” above) may be more pronounced for investments in developing countries because the economies of those countries are usually less diversified, communications, transportation and economic infrastructures are less developed, and developing countries ordinarily have less established legal, political, business and social frameworks. At times the prices of debt obligations of a developing country issuer may be extremely volatile. An issuer domiciled in a developed country may be similarly affected by these developing country risks to the extent that the issuer conducts its business in developing countries.

Foreign Currency Risk – Fluctuations in currency exchange rates can adversely affect the value of the Fund’s foreign investments. Such fluctuations may occur for a number of reasons, including market and economic conditions, or a government’s decision to devalue its currency or impose currency controls.

Structured Products Risk – Investments in securities that are backed by, or represent interests in, an underlying pool of securities or other assets, including investments in mortgage- and asset-backed securities and in collateralized mortgage obligations and collateralized debt obligations, involve the risks associated with the underlying assets (e.g., the risk of default by mortgagors whose mortgages are included in a mortgage-backed security or collateralized mortgage obligation), and may also involve different or greater risks, including the risk that distributions from the underlying assets will be inadequate to make interest or other payments to the Fund, the risk that the issuer of the securities will fail to administer the underlying assets properly or become insolvent, and the risk that the securities will be less liquid than other Fund investments.

 

Cybersecurity and Operational Risk – Operational failures, cyber-attacks or other disruptions that affect the Fund’s service providers, the Fund’s counterparties, other market participants or the issuers of securities held by the Fund may adversely affect the Fund and its shareholders, including by causing losses for the Fund or impairing Fund operations.

Additional information about Fund investments, investment strategies and risks of investing in the Fund appears beginning on page 118 of the Prospectus.
Risk Lose Money [Text] rr_RiskLoseMoney Accordingly, the loss of money is a risk of investing in the Fund.
RIsk Not Insured [Text] rr_RiskNotInsured An investment in the Fund is not a deposit in any bank and is not insured or guaranteed by the Federal Deposit Insurance Corporation or any other government agency.
Bar Chart and Performance Table [Heading] rr_BarChartAndPerformanceTableHeading Past Performance of the Fund
Performance Narrative [Text Block] rr_PerformanceNarrativeTextBlock

The following information provides some indication of the risks of investing in Strategic Income Fund by showing how the Fund’s investment results vary from year to year. The bar chart shows how the annual total return for Class A shares has been different in each full year shown. The average annual total return figures compare Class A, Class C and Class I performance to the Bloomberg Barclays US Universal Total Return Index Value Unhedged, a broad measure of market performance, and to a Blended Benchmark, comprised of 80% Bloomberg Barclays US Aggregate Bond Total Return Value USD, which represents a broad measure of bond market performance, and 20% MSCI World Net Total Return USD Index, which represents a broad measure of equity market performance in developed markets. Past performance (before and after taxes) is not necessarily an indication of how the Fund will perform in the future. The performance information shown is as of the calendar year ended December 31, 2021. Updated performance information may be obtained on the Thornburg website at Thornburg.com or by calling 1-800-847-0200.
Performance Information Illustrates Variability of Returns [Text] rr_PerformanceInformationIllustratesVariabilityOfReturns The following information provides some indication of the risks of investing in Strategic Income Fund by showing how the Fund’s investment results vary from year to year.
Performance Availability Phone [Text] rr_PerformanceAvailabilityPhone 1-800-847-0200
Performance Availability Website Address [Text] rr_PerformanceAvailabilityWebSiteAddress Thornburg.com
Performance Past Does Not Indicate Future [Text] rr_PerformancePastDoesNotIndicateFuture Past performance (before and after taxes) is not necessarily an indication of how the Fund will perform in the future.
Bar Chart [Heading] rr_BarChartHeading Annual Total Returns – Class A Shares
Bar Chart Does Not Reflect Sales Loads [Text] rr_BarChartDoesNotReflectSalesLoads The sales charge for Class A shares is not reflected in the returns shown in the bar chart above, and the returns would be less if the charge was taken into account.
Bar Chart Closing [Text Block] rr_BarChartClosingTextBlock

Total
Returns

Quarter
ended

Highest Quarterly Results

7.98%

6/30/2020

Lowest Quarterly Results

(5.71)%

3/31/2020

The sales charge for Class A shares is not reflected in the returns shown in the bar chart above, and the returns would be less if the charge was taken into account.
Performance Table Heading rr_PerformanceTableHeading Average Annual Total Returns (periods ended 12-31-21)
Performance Table Uses Highest Federal Rate rr_PerformanceTableUsesHighestFederalRate After-tax returns are calculated using the highest historical individual federal marginal income tax rates, and do not reflect state or local income taxes.
Performance Table Not Relevant to Tax Deferred rr_PerformanceTableNotRelevantToTaxDeferred Actual after-tax returns depend on an investor’s own tax situation and may differ from the returns shown, and after-tax returns shown are not relevant to investors who hold their Fund shares through tax-deferred arrangements, such as 401(k) plans or individual retirement accounts.
Performance Table One Class of after Tax Shown [Text] rr_PerformanceTableOneClassOfAfterTaxShown The after-tax returns shown relate only to Class A shares, and after-tax returns for other share classes will vary.
Performance Table Closing [Text Block] rr_PerformanceTableClosingTextBlock

After-tax returns are calculated using the highest historical individual federal marginal income tax rates, and do not reflect state or local income taxes. Actual after-tax returns depend on an investor’s own tax situation and may differ from the returns shown, and after-tax returns shown are not relevant to investors who hold their Fund shares through tax-deferred arrangements, such as 401(k) plans or individual retirement accounts. The after-tax returns shown relate only to Class A shares, and after-tax returns for other share classes will vary.
Retail | Thornburg Strategic Income Fund | Thornburg Strategic Income Fund - Class A  
Prospectus [Line Items] rr_ProspectusLineItems  
Trading Symbol dei_TradingSymbol TSIAX
Maximum Sales Charge Imposed on Purchases (as a percentage of Offering Price) rr_MaximumSalesChargeImposedOnPurchasesOverOfferingPrice 4.50%
Maximum Deferred Sales Charge (as a percentage) rr_MaximumDeferredSalesChargeOverOther none [39]
Management Fees (as a percentage of Assets) rr_ManagementFeesOverAssets 0.60%
Distribution and Service (12b-1) Fees rr_DistributionAndService12b1FeesOverAssets 0.25%
Other Expenses (as a percentage of Assets): rr_OtherExpensesOverAssets 0.20%
Expenses (as a percentage of Assets) rr_ExpensesOverAssets 1.05%
Fee Waiver or Reimbursement rr_FeeWaiverOrReimbursementOverAssets
Net Expenses (as a percentage of Assets) rr_NetExpensesOverAssets 1.05%
Expense Example, with Redemption, 1 Year rr_ExpenseExampleYear01 $ 552
Expense Example, with Redemption, 3 Years rr_ExpenseExampleYear03 769
Expense Example, with Redemption, 5 Years rr_ExpenseExampleYear05 1,003
Expense Example, with Redemption, 10 Years rr_ExpenseExampleYear10 $ 1,675
Annual Return 2012 rr_AnnualReturn2012 12.55%
Annual Return 2013 rr_AnnualReturn2013 5.89%
Annual Return 2014 rr_AnnualReturn2014 3.19%
Annual Return 2015 rr_AnnualReturn2015 (2.34%)
Annual Return 2016 rr_AnnualReturn2016 7.69%
Annual Return 2017 rr_AnnualReturn2017 6.01%
Annual Return 2018 rr_AnnualReturn2018 0.30%
Annual Return 2019 rr_AnnualReturn2019 7.55%
Annual Return 2020 rr_AnnualReturn2020 7.86%
Annual Return 2021 rr_AnnualReturn2021 2.43%
Highest Quarterly Return, Label rr_HighestQuarterlyReturnLabel Highest Quarterly Results
Highest Quarterly Return, Date rr_BarChartHighestQuarterlyReturnDate Jun. 30, 2020
Highest Quarterly Return rr_BarChartHighestQuarterlyReturn 7.98%
Lowest Quarterly Return, Label rr_LowestQuarterlyReturnLabel Lowest Quarterly Results
Lowest Quarterly Return, Date rr_BarChartLowestQuarterlyReturnDate Mar. 31, 2020
Lowest Quarterly Return rr_BarChartLowestQuarterlyReturn (5.71%)
1 Year rr_AverageAnnualReturnYear01 (2.21%)
5 Years rr_AverageAnnualReturnYear05 3.83%
10 Years rr_AverageAnnualReturnYear10 4.55%
Retail | Thornburg Strategic Income Fund | Thornburg Strategic Income Fund - Class A | After Taxes on Distributions  
Prospectus [Line Items] rr_ProspectusLineItems  
1 Year rr_AverageAnnualReturnYear01 (3.70%)
5 Years rr_AverageAnnualReturnYear05 2.40%
10 Years rr_AverageAnnualReturnYear10 2.72%
Retail | Thornburg Strategic Income Fund | Thornburg Strategic Income Fund - Class A | After Taxes on Distributions and Sales  
Prospectus [Line Items] rr_ProspectusLineItems  
1 Year rr_AverageAnnualReturnYear01 (1.31%)
5 Years rr_AverageAnnualReturnYear05 2.30%
10 Years rr_AverageAnnualReturnYear10 2.69%
Retail | Thornburg Strategic Income Fund | Thornburg Strategic Income Fund - Class A | Bloomberg Barclays US Universal Total Return Index Value Unhedged (reflects no deduction for fees, expenses, or taxes)  
Prospectus [Line Items] rr_ProspectusLineItems  
1 Year rr_AverageAnnualReturnYear01 (1.10%)
5 Years rr_AverageAnnualReturnYear05 3.84%
10 Years rr_AverageAnnualReturnYear10 3.31%
Retail | Thornburg Strategic Income Fund | Thornburg Strategic Income Fund - Class A | Blended Benchmark (reflects no deduction for fees, expenses, or U.S. taxes)  
Prospectus [Line Items] rr_ProspectusLineItems  
1 Year rr_AverageAnnualReturnYear01 2.85%
5 Years rr_AverageAnnualReturnYear05 5.97%
10 Years rr_AverageAnnualReturnYear10 4.95%
Retail | Thornburg Strategic Income Fund | Thornburg Strategic Income Fund - Class C  
Prospectus [Line Items] rr_ProspectusLineItems  
Trading Symbol dei_TradingSymbol TSICX
Maximum Sales Charge Imposed on Purchases (as a percentage of Offering Price) rr_MaximumSalesChargeImposedOnPurchasesOverOfferingPrice none
Maximum Deferred Sales Charge (as a percentage) rr_MaximumDeferredSalesChargeOverOther 1.00% [40]
Management Fees (as a percentage of Assets) rr_ManagementFeesOverAssets 0.60%
Distribution and Service (12b-1) Fees rr_DistributionAndService12b1FeesOverAssets 1.00%
Other Expenses (as a percentage of Assets): rr_OtherExpensesOverAssets 0.23%
Expenses (as a percentage of Assets) rr_ExpensesOverAssets 1.83%
Fee Waiver or Reimbursement rr_FeeWaiverOrReimbursementOverAssets (0.03%) [41]
Net Expenses (as a percentage of Assets) rr_NetExpensesOverAssets 1.80%
Expense Example, with Redemption, 1 Year rr_ExpenseExampleYear01 $ 283
Expense Example, with Redemption, 3 Years rr_ExpenseExampleYear03 573
Expense Example, with Redemption, 5 Years rr_ExpenseExampleYear05 988
Expense Example, with Redemption, 10 Years rr_ExpenseExampleYear10 2,145
Expense Example, No Redemption, 1 Year rr_ExpenseExampleNoRedemptionYear01 183
Expense Example, No Redemption, 3 Years rr_ExpenseExampleNoRedemptionYear03 573
Expense Example, No Redemption, 5 Years rr_ExpenseExampleNoRedemptionYear05 988
Expense Example, No Redemption, 10 Years rr_ExpenseExampleNoRedemptionYear10 $ 2,145
1 Year rr_AverageAnnualReturnYear01 0.64%
5 Years rr_AverageAnnualReturnYear05 4.01%
10 Years rr_AverageAnnualReturnYear10 4.35%
Retail | Thornburg Strategic Income Fund | Thornburg Strategic Income Fund - Class C | Bloomberg Barclays US Universal Total Return Index Value Unhedged (reflects no deduction for fees, expenses, or taxes)  
Prospectus [Line Items] rr_ProspectusLineItems  
1 Year rr_AverageAnnualReturnYear01 (1.10%)
5 Years rr_AverageAnnualReturnYear05 3.84%
10 Years rr_AverageAnnualReturnYear10 3.31%
Retail | Thornburg Strategic Income Fund | Thornburg Strategic Income Fund - Class C | Blended Benchmark (reflects no deduction for fees, expenses, or U.S. taxes)  
Prospectus [Line Items] rr_ProspectusLineItems  
1 Year rr_AverageAnnualReturnYear01 2.85%
5 Years rr_AverageAnnualReturnYear05 5.97%
10 Years rr_AverageAnnualReturnYear10 4.95%
Retail | Thornburg Strategic Income Fund | Thornburg Strategic Income Fund - Class I  
Prospectus [Line Items] rr_ProspectusLineItems  
Trading Symbol dei_TradingSymbol TSIIX
Maximum Sales Charge Imposed on Purchases (as a percentage of Offering Price) rr_MaximumSalesChargeImposedOnPurchasesOverOfferingPrice none
Maximum Deferred Sales Charge (as a percentage) rr_MaximumDeferredSalesChargeOverOther none
Management Fees (as a percentage of Assets) rr_ManagementFeesOverAssets 0.60%
Distribution and Service (12b-1) Fees rr_DistributionAndService12b1FeesOverAssets none
Other Expenses (as a percentage of Assets): rr_OtherExpensesOverAssets 0.21%
Expenses (as a percentage of Assets) rr_ExpensesOverAssets 0.81%
Fee Waiver or Reimbursement rr_FeeWaiverOrReimbursementOverAssets (0.21%) [41]
Net Expenses (as a percentage of Assets) rr_NetExpensesOverAssets 0.60%
Expense Example, with Redemption, 1 Year rr_ExpenseExampleYear01 $ 61
Expense Example, with Redemption, 3 Years rr_ExpenseExampleYear03 238
Expense Example, with Redemption, 5 Years rr_ExpenseExampleYear05 429
Expense Example, with Redemption, 10 Years rr_ExpenseExampleYear10 $ 982
1 Year rr_AverageAnnualReturnYear01 2.78%
5 Years rr_AverageAnnualReturnYear05 5.17%
10 Years rr_AverageAnnualReturnYear10 5.39%
Retail | Thornburg Strategic Income Fund | Thornburg Strategic Income Fund - Class I | Bloomberg Barclays US Universal Total Return Index Value Unhedged (reflects no deduction for fees, expenses, or taxes)  
Prospectus [Line Items] rr_ProspectusLineItems  
1 Year rr_AverageAnnualReturnYear01 (1.10%)
5 Years rr_AverageAnnualReturnYear05 3.84%
10 Years rr_AverageAnnualReturnYear10 3.31%
Retail | Thornburg Strategic Income Fund | Thornburg Strategic Income Fund - Class I | Blended Benchmark (reflects no deduction for fees, expenses, or U.S. taxes)  
Prospectus [Line Items] rr_ProspectusLineItems  
1 Year rr_AverageAnnualReturnYear01 2.85%
5 Years rr_AverageAnnualReturnYear05 5.97%
10 Years rr_AverageAnnualReturnYear10 4.95%
Retail | Thornburg Short Duration Municipal Fund  
Prospectus [Line Items] rr_ProspectusLineItems  
Risk/Return [Heading] rr_RiskReturnHeading Short Duration Municipal Fund
Objective [Heading] rr_ObjectiveHeading Investment Goal
Objective, Primary [Text Block] rr_ObjectivePrimaryTextBlock

The Fund seeks current income exempt from federal income tax, consistent with preservation of capital.
Expense [Heading] rr_ExpenseHeading Fees and Expenses of the Fund
Expense Narrative [Text Block] rr_ExpenseNarrativeTextBlock

This table describes the fees and expenses that you may pay if you buy and hold shares of the Fund. You may qualify for discounts from the sales charges applicable to Class A shares if you or other qualifying account holders invest, or agree to invest in the future, at least $50,000 in the Thornburg Funds. More information about this and other discounts and sales charge waivers is available from your financial intermediary, in the Prospectus under the captions “Class A Sales Charge Waivers,” beginning on page 146, and “Appendix A – Sales Charge Waivers Offered by Financial Intermediaries,” beginning on page 200, and in the Statement of Additional Information under the caption “Additional Information Respecting Purchase and Redemption of Shares,” beginning on page 108.
Shareholder Fees Caption [Text] rr_ShareholderFeesCaption Shareholder Fees (fees paid directly from your investment)
Operating Expenses Caption [Text] rr_OperatingExpensesCaption Annual Fund Operating Expenses (expenses that you pay each year as a percentage of the value of your investment)
Fee Waiver or Reimbursement over Assets, Date of Termination rr_FeeWaiverOrReimbursementOverAssetsDateOfTermination February 1, 2023
Portfolio Turnover [Heading] rr_PortfolioTurnoverHeading Portfolio Turnover.
Portfolio Turnover [Text Block] rr_PortfolioTurnoverTextBlock

The Fund pays transaction costs, such as commissions, when it buys and sells securities (or “turns over”) its portfolio. A higher portfolio turnover rate may indicate higher transaction costs and may result in higher taxes when Fund shares are held in a taxable account. These costs, which are not reflected in Annual Fund Operating Expenses or in the Example, affect the Fund’s performance. During the most recent fiscal year, the Fund’s portfolio turnover rate was 34.71% of the average value of its portfolio.
Portfolio Turnover, Rate rr_PortfolioTurnoverRate 34.71%
Expense Breakpoint Discounts [Text] rr_ExpenseBreakpointDiscounts You may qualify for discounts from the sales charges applicable to Class A shares if you or other qualifying account holders invest, or agree to invest in the future, at least $50,000 in the Thornburg Funds.
Expense Breakpoint, Minimum Investment Required [Amount] rr_ExpenseBreakpointMinimumInvestmentRequiredAmount $ 50,000
Expense Example [Heading] rr_ExpenseExampleHeading Example.
Expense Example Narrative [Text Block] rr_ExpenseExampleNarrativeTextBlock

This Example is intended to help you compare the cost of investing in the Fund with the cost of investing in other mutual funds.

The Example assumes that you invest $10,000 in the Fund for the time periods indicated and then redeem all of your shares at the end of those periods. The Example also assumes that your investment has a 5% return each year, dividends and distributions are reinvested, and that the Fund’s operating expenses remain the same. Although your actual costs may be higher or lower, based on these assumptions (and giving effect to fee waivers and expense reimbursements in the first year) your costs would be:
Strategy [Heading] rr_StrategyHeading Principal Investment Strategies
Strategy Narrative [Text Block] rr_StrategyNarrativeTextBlock

The Fund pursues its primary goal by investing principally in a laddered maturity portfolio of municipal obligations issued by states and state agencies, local governments and their agencies and by United States territories and possessions. Thornburg Investment Management, Inc. (“Thornburg”) actively manages the Fund’s portfolio. Investment decisions are based upon outlooks for interest rates and securities markets, the supply of municipal debt obligations, and analysis of specific securities. The Fund invests in obligations and participations in obligations which are rated by a nationally recognized statistical rating organization at the time of purchase as investment grade or, if unrated, are issued by obligors which Thornburg determines have comparable investment grade obligations outstanding or which are deemed by Thornburg to be comparable to obligors with outstanding investment grade obligations. “Participations” are undivided interests in pools of securities where the underlying credit support passes through to the participants. The Fund’s portfolio is “laddered” by investing in obligations of different maturities so that some obligations mature during each of the coming years.

Because the magnitude of changes in value of interest-bearing obligations is greater for obligations with longer durations given an equivalent change in interest rates, the Fund seeks to reduce changes in its share value compared to longer duration fixed income portfolios by maintaining a portfolio of investments with a dollar-weighted average duration of normally no more than three years. Duration is a measure of estimated sensitivity to interest rate changes, and a debt obligation or a portfolio of obligations with a higher duration will typically be more sensitive to interest rate changes than an obligation or a portfolio with a lower duration. Duration is commonly expressed as a number, which is the expected percentage change in an obligation’s price upon a 1% change in interest rates. For example, an obligation with a duration of 3 would be expected to change in price by approximately 3% in response to a 1% change in interest rates. During temporary periods the Fund’s average duration and average portfolio maturity may be further reduced for defensive purposes. There is no limitation on the duration or maturity of any specific security the Fund may purchase. The Fund may dispose of any security before it matures. The Fund also attempts to reduce changes in its share value through credit analysis, selection and diversification.

The Fund ordinarily acquires and holds securities for investment rather than for realization of gains by short-term trading on market fluctuations. However, it may sell an investment prior to its scheduled maturity date to enhance income or reduce loss, to change the portfolio’s average duration or average maturity, to pursue other investment opportunities, in response to changes in the conditions or business of the investment’s issuer or changes in overall market conditions, or if, in Thornburg’s opinion, the investment no longer serves to achieve the Fund’s investment goals.  The objective of preserving capital may prevent the Fund from obtaining the highest yields available.

The Fund normally invests 100% of its assets in municipal obligations, the income from which is exempt from the regular federal income tax. The Fund may invest up to 20% of its assets in taxable securities which would produce income not exempt from federal income tax because of market conditions, pending investment of idle funds or to afford liquidity. The Fund’s temporary taxable investments may exceed 20% of its assets when made for defensive purposes during periods of abnormal market conditions. If the Fund found it necessary to own taxable investments, some of its income would be subject to federal income tax.
Risk [Heading] rr_RiskHeading Principal Investment Risks
Risk Narrative [Text Block] rr_RiskNarrativeTextBlock

An investment in the Fund is not a deposit in any bank and is not insured or guaranteed by the Federal Deposit Insurance Corporation or any other government agency. Accordingly, the loss of money is a risk of investing in the Fund. The value of the Fund’s shares and its dividends may fluctuate from day to day and over time, and when you sell your shares they may be worth less than what you paid for them. The Fund seeks higher income than is typically available, across market cycles, from investment in a money market fund. Consequently, if your sole objective is preservation of capital, then the Fund may not be suitable for you because the Fund’s share value will fluctuate, including as interest rates change. Investors whose sole objective is preservation of capital may wish to consider a high quality money market fund. The following is a summary of the principal risks of investing in the Fund.

Management Risk – The Fund is an actively managed portfolio, and the value of the Fund may be reduced if Thornburg pursues unsuccessful investments or fails to correctly identify risks affecting the broad economy or specific issuers in which the Fund invests.

Interest Rate Risk – When interest rates increase, the value of the Fund’s investments may decline and the Fund’s share value may be reduced. This effect is typically more pronounced for intermediate and longer-term obligations. When interest rates decrease, the Fund’s dividends may decline. Decreases in market interest rates may also result in prepayments of obligations the Fund acquires, requiring the Fund to reinvest at lower interest rates.

Credit Risk – If obligations held by the Fund are downgraded by ratings agencies or go into default, or if legislation or other government action reduces the ability of issuers to pay principal and interest when due, the value of those obligations may decline and the Fund’s share value and any dividends paid by the Fund may be reduced. For example, municipal leases held by the Fund may be subject to non-appropriation provisions which permit governmental agencies or issuers to discontinue payments to the Fund under the municipal leases.

Market and Economic Risk – The value of the Fund’s investments may decline and its share value may be reduced due to changes in general economic and market conditions. This effect is typically more pronounced for the Fund’s investments in lower rated and unrated municipal obligations, the value of which may fluctuate more significantly in response to poor economic growth or other changes in market conditions, political, economic and legal developments, and developments affecting specific issuers.

Liquidity Risk – Due to a lack of demand in the marketplace or other factors, the Fund may not be able to sell promptly some or all of the obligations that it holds, or may only be able to sell obligations at less than desired prices.

Cybersecurity and Operational Risk – Operational failures, cyber-attacks or other disruptions that affect the Fund’s service providers, the Fund’s counterparties, other market participants or the issuers of securities held by the Fund may adversely affect the Fund and its shareholders, including by causing losses for the Fund or impairing Fund operations.

Additional information about Fund investments, investment strategies and risks of investing in the Fund appears beginning on page 118 of the Prospectus.
Risk Lose Money [Text] rr_RiskLoseMoney Accordingly, the loss of money is a risk of investing in the Fund.
RIsk Not Insured [Text] rr_RiskNotInsured An investment in the Fund is not a deposit in any bank and is not insured or guaranteed by the Federal Deposit Insurance Corporation or any other government agency.
Bar Chart and Performance Table [Heading] rr_BarChartAndPerformanceTableHeading Past Performance of the Fund
Performance Narrative [Text Block] rr_PerformanceNarrativeTextBlock

The following information provides some indication of the risks of investing in Short Duration Municipal Fund by showing how the Fund’s investment results vary from year to year. The bar chart shows how the annual total returns for Class A shares have been different in each full year shown. The average annual total return figures compare Class A and Class I share performance to the ICE BofAML 1-3 Year U.S. Municipal Securities Index, a broad measure of market performance. Past performance (before and after taxes) is not necessarily an indication of how the Fund will perform in the future. The performance information shown is as of the calendar year ended December 31, 2021. Updated performance information may be obtained on the Thornburg website at Thornburg.com or by calling 1-800-847-0200.
Performance Information Illustrates Variability of Returns [Text] rr_PerformanceInformationIllustratesVariabilityOfReturns The following information provides some indication of the risks of investing in Short Duration Municipal Fund by showing how the Fund’s investment results vary from year to year.
Performance Availability Phone [Text] rr_PerformanceAvailabilityPhone 1-800-847-0200
Performance Availability Website Address [Text] rr_PerformanceAvailabilityWebSiteAddress Thornburg.com
Performance Past Does Not Indicate Future [Text] rr_PerformancePastDoesNotIndicateFuture Past performance (before and after taxes) is not necessarily an indication of how the Fund will perform in the future.
Bar Chart [Heading] rr_BarChartHeading Annual Total Returns – Class A Shares
Bar Chart Does Not Reflect Sales Loads [Text] rr_BarChartDoesNotReflectSalesLoads The sales charge for Class A shares is not reflected in the returns shown in the bar chart above, and the returns would be less if the charge was taken into account.
Bar Chart Closing [Text Block] rr_BarChartClosingTextBlock

Total
Returns

Quarter ended

Highest Quarterly Results

0.92%

6/30/2020

Lowest Quarterly Results

(0.51)%

3/31/2020

The sales charge for Class A shares is not reflected in the returns shown in the bar chart above, and the returns would be less if the charge was taken into account.
Performance Table Heading rr_PerformanceTableHeading Average Annual Total Returns (periods ended 12-31-21)
Performance Table Uses Highest Federal Rate rr_PerformanceTableUsesHighestFederalRate After-tax returns are calculated using the highest historical individual federal marginal income tax rates, and do not reflect state or local income taxes.
Performance Table Not Relevant to Tax Deferred rr_PerformanceTableNotRelevantToTaxDeferred Actual after-tax returns depend on an investor’s own tax situation, and may differ from the returns shown, and after-tax returns shown are not relevant to investors who hold their Fund shares through tax-deferred arrangements, such as 401(k) plans or individual retirement accounts.
Performance Table One Class of after Tax Shown [Text] rr_PerformanceTableOneClassOfAfterTaxShown The after-tax returns shown relate only to Class A shares, and after-tax returns for other share classes will vary.
Performance Table Closing [Text Block] rr_PerformanceTableClosingTextBlock

After-tax returns are calculated using the highest historical individual federal marginal income tax rates, and do not reflect state or local income taxes. Actual after-tax returns depend on an investor’s own tax situation, and may differ from the returns shown, and after-tax returns shown are not relevant to investors who hold their Fund shares through tax-deferred arrangements, such as 401(k) plans or individual retirement accounts. The after-tax returns shown relate only to Class A shares, and after-tax returns for other share classes will vary.
Retail | Thornburg Short Duration Municipal Fund | Thornburg Short Duration Municipal Fund Class A  
Prospectus [Line Items] rr_ProspectusLineItems  
Trading Symbol dei_TradingSymbol TLMAX
Maximum Sales Charge Imposed on Purchases (as a percentage of Offering Price) rr_MaximumSalesChargeImposedOnPurchasesOverOfferingPrice 2.25%
Maximum Deferred Sales Charge (as a percentage) rr_MaximumDeferredSalesChargeOverOther none [42]
Management Fees (as a percentage of Assets) rr_ManagementFeesOverAssets 0.40%
Distribution and Service (12b-1) Fees rr_DistributionAndService12b1FeesOverAssets 0.20%
Other Expenses (as a percentage of Assets): rr_OtherExpensesOverAssets 0.38%
Expenses (as a percentage of Assets) rr_ExpensesOverAssets 0.98%
Fee Waiver or Reimbursement rr_FeeWaiverOrReimbursementOverAssets (0.28%) [43]
Net Expenses (as a percentage of Assets) rr_NetExpensesOverAssets 0.70%
Expense Example, with Redemption, 1 Year rr_ExpenseExampleYear01 $ 295
Expense Example, with Redemption, 3 Years rr_ExpenseExampleYear03 503
Expense Example, with Redemption, 5 Years rr_ExpenseExampleYear05 728
Expense Example, with Redemption, 10 Years rr_ExpenseExampleYear10 $ 1,374
Annual Return 2014 rr_AnnualReturn2014 0.35%
Annual Return 2015 rr_AnnualReturn2015 0.14%
Annual Return 2016 rr_AnnualReturn2016 0.01%
Annual Return 2017 rr_AnnualReturn2017 0.89%
Annual Return 2018 rr_AnnualReturn2018 0.84%
Annual Return 2019 rr_AnnualReturn2019 1.91%
Annual Return 2020 rr_AnnualReturn2020 0.87%
Annual Return 2021 rr_AnnualReturn2021 (0.25%)
Highest Quarterly Return, Label rr_HighestQuarterlyReturnLabel Highest Quarterly Results
Highest Quarterly Return, Date rr_BarChartHighestQuarterlyReturnDate Jun. 30, 2020
Highest Quarterly Return rr_BarChartHighestQuarterlyReturn 0.92%
Lowest Quarterly Return, Label rr_LowestQuarterlyReturnLabel Lowest Quarterly Results
Lowest Quarterly Return, Date rr_BarChartLowestQuarterlyReturnDate Mar. 31, 2020
Lowest Quarterly Return rr_BarChartLowestQuarterlyReturn (0.51%)
1 Year rr_AverageAnnualReturnYear01 (2.46%)
5 Years rr_AverageAnnualReturnYear05 0.54%
Since Inception rr_AverageAnnualReturnSinceInception 0.40%
Inception Date rr_AverageAnnualReturnInceptionDate Dec. 30, 2013
Retail | Thornburg Short Duration Municipal Fund | Thornburg Short Duration Municipal Fund Class A | After Taxes on Distributions  
Prospectus [Line Items] rr_ProspectusLineItems  
1 Year rr_AverageAnnualReturnYear01 (2.46%)
5 Years rr_AverageAnnualReturnYear05 0.54%
Since Inception rr_AverageAnnualReturnSinceInception 0.40%
Retail | Thornburg Short Duration Municipal Fund | Thornburg Short Duration Municipal Fund Class A | After Taxes on Distributions and Sales  
Prospectus [Line Items] rr_ProspectusLineItems  
1 Year rr_AverageAnnualReturnYear01 (1.36%)
5 Years rr_AverageAnnualReturnYear05 0.61%
Since Inception rr_AverageAnnualReturnSinceInception 0.45%
Retail | Thornburg Short Duration Municipal Fund | Thornburg Short Duration Municipal Fund Class A | ICE BofAML 1-3 Year U.S. Municipal Securities Index (reflects no deduction for fees, expenses, or taxes)  
Prospectus [Line Items] rr_ProspectusLineItems  
1 Year rr_AverageAnnualReturnYear01 0.34%
5 Years rr_AverageAnnualReturnYear05 1.62%
Since Inception rr_AverageAnnualReturnSinceInception 1.24%
Retail | Thornburg Short Duration Municipal Fund | Thornburg Short Duration Municipal Fund Class I  
Prospectus [Line Items] rr_ProspectusLineItems  
Trading Symbol dei_TradingSymbol TLMIX
Maximum Sales Charge Imposed on Purchases (as a percentage of Offering Price) rr_MaximumSalesChargeImposedOnPurchasesOverOfferingPrice none
Maximum Deferred Sales Charge (as a percentage) rr_MaximumDeferredSalesChargeOverOther none
Management Fees (as a percentage of Assets) rr_ManagementFeesOverAssets 0.40%
Distribution and Service (12b-1) Fees rr_DistributionAndService12b1FeesOverAssets none
Other Expenses (as a percentage of Assets): rr_OtherExpensesOverAssets 0.25%
Expenses (as a percentage of Assets) rr_ExpensesOverAssets 0.65%
Fee Waiver or Reimbursement rr_FeeWaiverOrReimbursementOverAssets (0.15%) [43]
Net Expenses (as a percentage of Assets) rr_NetExpensesOverAssets 0.50%
Expense Example, with Redemption, 1 Year rr_ExpenseExampleYear01 $ 51
Expense Example, with Redemption, 3 Years rr_ExpenseExampleYear03 193
Expense Example, with Redemption, 5 Years rr_ExpenseExampleYear05 347
Expense Example, with Redemption, 10 Years rr_ExpenseExampleYear10 $ 796
1 Year rr_AverageAnnualReturnYear01 (0.05%)
5 Years rr_AverageAnnualReturnYear05 1.05%
Since Inception rr_AverageAnnualReturnSinceInception 0.78%
Inception Date rr_AverageAnnualReturnInceptionDate Dec. 30, 2013
Retail | Thornburg Short Duration Municipal Fund | Thornburg Short Duration Municipal Fund Class I | ICE BofAML 1-3 Year U.S. Municipal Securities Index (reflects no deduction for fees, expenses, or taxes)  
Prospectus [Line Items] rr_ProspectusLineItems  
1 Year rr_AverageAnnualReturnYear01 0.34%
5 Years rr_AverageAnnualReturnYear05 1.62%
Since Inception rr_AverageAnnualReturnSinceInception 1.24%
Retail | Thornburg Limited Term Municipal Fund  
Prospectus [Line Items] rr_ProspectusLineItems  
Risk/Return [Heading] rr_RiskReturnHeading Limited Term Municipal Fund
Objective [Heading] rr_ObjectiveHeading Investment Goal
Objective, Primary [Text Block] rr_ObjectivePrimaryTextBlock

The primary investment goal of Limited Term Municipal Fund is to obtain as high a level of current income exempt from federal individual income tax as is consistent, in the view of the Fund’s investment advisor, with preservation of capital.
Objective, Secondary [Text Block] rr_ObjectiveSecondaryTextBlock

The secondary goal of the Fund is to reduce expected changes in its share price compared to longer intermediate and long-term bond portfolios.

Expense [Heading] rr_ExpenseHeading Fees and Expenses of the Fund
Expense Narrative [Text Block] rr_ExpenseNarrativeTextBlock

This table describes the fees and expenses that you may pay if you buy and hold shares of the Fund. You may qualify for discounts from the sales charges applicable to Class A shares if you or other qualifying account holders invest, or agree to invest in the future, at least $50,000 in the Thornburg Funds. More information about this and other discounts and sales charge waivers is available from your financial intermediary, in the Prospectus under the captions “Class A Sales Charge Waivers,” beginning on page 146, and “Appendix A – Sales Charge Waivers Offered by Financial Intermediaries,” beginning on page 200, and in the Statement of Additional Information under the caption “Additional Information Respecting Purchase and Redemption of Shares,” beginning on page 108.
Shareholder Fees Caption [Text] rr_ShareholderFeesCaption Shareholder Fees (fees paid directly from your investment)
Operating Expenses Caption [Text] rr_OperatingExpensesCaption Annual Fund Operating Expenses (expenses that you pay each year as a percentage of the value of your investment)
Fee Waiver or Reimbursement over Assets, Date of Termination rr_FeeWaiverOrReimbursementOverAssetsDateOfTermination February 1, 2023
Portfolio Turnover [Heading] rr_PortfolioTurnoverHeading Portfolio Turnover.
Portfolio Turnover [Text Block] rr_PortfolioTurnoverTextBlock

The Fund pays transaction costs, such as commissions, when it buys and sells securities (or “turns over”) its portfolio. A higher portfolio turnover rate may indicate higher transaction costs and may result in higher taxes when Fund shares are held in a taxable account. These costs, which are not reflected in Annual Fund Operating Expenses or in the Example, affect the Fund’s performance. During the most recent fiscal year, the Fund’s portfolio turnover rate was 22.29% of the average value of its portfolio.
Portfolio Turnover, Rate rr_PortfolioTurnoverRate 22.29%
Expense Breakpoint Discounts [Text] rr_ExpenseBreakpointDiscounts You may qualify for discounts from the sales charges applicable to Class A shares if you or other qualifying account holders invest, or agree to invest in the future, at least $50,000 in the Thornburg Funds.
Expense Breakpoint, Minimum Investment Required [Amount] rr_ExpenseBreakpointMinimumInvestmentRequiredAmount $ 50,000
Expense Example [Heading] rr_ExpenseExampleHeading Example.
Expense Example Narrative [Text Block] rr_ExpenseExampleNarrativeTextBlock

This Example is intended to help you compare the cost of investing in the Fund with the cost of investing in other mutual funds.

The Example assumes that you invest $10,000 in the Fund for the time periods indicated and then redeem all of your shares at the end of those periods. The Example also assumes that your investment has a 5% return each year, dividends and distributions are reinvested, and that the Fund’s operating expenses remain the same. Although your actual costs may be higher or lower, based on these assumptions your costs would be:
Expense Example, No Redemption Narrative [Text Block] rr_ExpenseExampleNoRedemptionNarrativeTextBlock

You would pay the following expenses if you did not redeem your Class C shares:
Strategy [Heading] rr_StrategyHeading Principal Investment Strategies
Strategy Narrative [Text Block] rr_StrategyNarrativeTextBlock

The Fund pursues its primary goal by investing principally in a laddered maturity portfolio of municipal obligations issued by states and state agencies, local governments and their agencies and by United States territories and possessions. Thornburg Investment Management, Inc. (“Thornburg”) actively manages the Fund’s portfolio. Investment decisions are based upon outlooks for interest rates and securities markets, the supply of municipal debt obligations, and analysis of specific securities. The Fund invests in obligations and participations in obligations which are rated by a nationally recognized statistical rating organization at the time of purchase as investment grade or, if unrated, are issued by obligors which Thornburg determines have comparable investment grade obligations outstanding or which are deemed by Thornburg to be comparable to obligors with outstanding investment grade obligations. “Participations” are undivided interests in pools of securities where the underlying credit support passes through to the participants. The Fund’s portfolio is “laddered” by investing in obligations of different maturities so that some obligations mature during each of the coming years.

Because the magnitude of changes in value of interest-bearing obligations is greater for obligations with longer terms given an equivalent change in interest rates, the Fund seeks to reduce changes in its share value by maintaining a portfolio of investments with a dollar-weighted average maturity normally less than five years. As a result, the Fund also maintains a portfolio of investments having a dollar-weighted average effective duration of normally no more than five years. Duration is a measure of estimated sensitivity to interest rate changes. A portfolio with a longer average effective duration will typically be more sensitive to interest rate changes than a portfolio with a shorter average effective duration. Duration is commonly expressed as a number, which is the expected percentage change in an obligation’s price upon a 1% change in interest rates. For example, an obligation with a duration of 5 would be expected to change in price by approximately 5% in response to a 1% change in interest rates. During temporary periods the Fund’s portfolio maturity and average effective duration may be reduced for defensive purposes. There is no limitation on the maturity of any specific security the Fund may purchase. The Fund may dispose of any security before it matures. The Fund also attempts to reduce changes in its share value through credit analysis, selection and diversification.

The Fund ordinarily acquires and holds securities for investment rather than for realization of gains by short-term trading on market fluctuations. However, it may sell an investment prior to its scheduled maturity date to enhance income or reduce loss, to change the portfolio’s average duration or average maturity, to pursue other investment opportunities, in response to changes in the conditions or business of the investment’s issuer or changes in overall market conditions, or if, in Thornburg’s opinion, the investment no longer serves to achieve the Fund’s investment goals.  The objective of preserving capital may prevent the Fund from obtaining the highest yields available.

The Fund normally invests 100% of its assets in municipal obligations, the income from which is exempt from the regular federal income tax. The Fund may invest up to 20% of its assets in taxable securities which would produce income not exempt from federal income tax because of market conditions, pending investment of idle funds or to afford liquidity. The Fund’s temporary taxable investments may exceed 20% of its assets when made for defensive purposes during periods of abnormal market conditions. If the Fund found it necessary to own taxable investments, some of its income would be subject to federal income tax.
Risk [Heading] rr_RiskHeading Principal Investment Risks
Risk Narrative [Text Block] rr_RiskNarrativeTextBlock

An investment in the Fund is not a deposit in any bank and is not insured or guaranteed by the Federal Deposit Insurance Corporation or any other government agency. Accordingly, the loss of money is a risk of investing in the Fund. The value of the Fund’s shares and its dividends may fluctuate from day to day and over time, and when you sell your shares they may be worth less than what you paid for them. The following is a summary of the principal risks of investing in the Fund.

Management Risk – The Fund is an actively managed portfolio, and the value of the Fund may be reduced if Thornburg pursues unsuccessful investments or fails to correctly identify risks affecting the broad economy or specific issuers in which the Fund invests.

Interest Rate Risk – When interest rates increase, the value of the Fund’s investments may decline and the Fund’s share value may be reduced. This effect is typically more pronounced for intermediate and longer-term obligations. When interest rates decrease, the Fund’s dividends may decline. Decreases in market interest rates may also result in prepayments of obligations the Fund acquires, requiring the Fund to reinvest at lower interest rates.

Credit Risk – If obligations held by the Fund are downgraded by ratings agencies or go into default, or if legislation or other government action reduces the ability of issuers to pay principal and interest when due, the value of those obligations may decline and the Fund’s share value and the dividends paid by the Fund may be reduced. Lower-rated or unrated obligations held by the Fund may have, or may be perceived to have, greater risk of default and ratings downgrades. For example, municipal leases held by the Fund may be subject to non-appropriation provisions which permit governmental agencies or issuers to discontinue payments to the Fund under the municipal leases.

Market and Economic Risk – The value of the Fund’s investments may decline and its share value may be reduced due to changes in general economic and market conditions. This effect is typically more pronounced for the Fund’s investments in lower-rated and unrated municipal obligations, the value of which may fluctuate more significantly in response to poor economic growth or other changes in market conditions, political, economic and legal developments, and developments affecting specific issuers.

Liquidity Risk – Due to a lack of demand in the marketplace or other factors, the Fund may not be able to sell promptly some or all of the obligations that it holds, or may only be able to sell obligations at less than desired prices. The market for lower-rated and unrated obligations may be less liquid than the market for other obligations, making it difficult for the Fund to value its investment in a lower-rated or unrated obligation or to sell the investment in a timely manner or at an acceptable price.

Cybersecurity and Operational Risk – Operational failures, cyber-attacks or other disruptions that affect the Fund’s service providers, the Fund’s counterparties, other market participants or the issuers of securities held by the Fund may adversely affect the Fund and its shareholders, including by causing losses for the Fund or impairing Fund operations.

Additional information about Fund investments, investment strategies and risks of investing in the Fund appears beginning on page 118 of the Prospectus.
Risk Lose Money [Text] rr_RiskLoseMoney Accordingly, the loss of money is a risk of investing in the Fund.
RIsk Not Insured [Text] rr_RiskNotInsured An investment in the Fund is not a deposit in any bank and is not insured or guaranteed by the Federal Deposit Insurance Corporation or any other government agency.
Bar Chart and Performance Table [Heading] rr_BarChartAndPerformanceTableHeading Past Performance of the Fund
Performance Narrative [Text Block] rr_PerformanceNarrativeTextBlock

The following information provides some indication of the risks of investing in Limited Term Municipal Fund by showing how the Fund’s investment results vary from year to year. The bar chart shows how the annual total returns for Class A shares have been different in each full year shown. The average annual total return figures compare Class A, Class C, Class C2 and Class I share performance to the ICE BofAML 1-10 Year U.S. Municipal Securities Index, a broad measure of market

performance. Past performance (before and after taxes) is not necessarily an indication of how the Fund will perform in the future. The performance information shown is as of the calendar year ended December 31, 2021. Updated performance information may be obtained on the Thornburg website at Thornburg.com or by calling 1-800-847-0200.
Performance Information Illustrates Variability of Returns [Text] rr_PerformanceInformationIllustratesVariabilityOfReturns The following information provides some indication of the risks of investing in Limited Term Municipal Fund by showing how the Fund’s investment results vary from year to year.
Performance Availability Phone [Text] rr_PerformanceAvailabilityPhone 1-800-847-0200
Performance Availability Website Address [Text] rr_PerformanceAvailabilityWebSiteAddress Thornburg.com
Performance Past Does Not Indicate Future [Text] rr_PerformancePastDoesNotIndicateFuture Past performance (before and after taxes) is not necessarily an indication of how the Fund will perform in the future.
Bar Chart [Heading] rr_BarChartHeading Annual Total Returns – Class A Shares
Bar Chart Does Not Reflect Sales Loads [Text] rr_BarChartDoesNotReflectSalesLoads The sales charge for Class A shares is not reflected in the returns shown in the bar chart above, and the returns would be less if the charge was taken into account.
Bar Chart Closing [Text Block] rr_BarChartClosingTextBlock

Total
Returns

Quarter
ended

Highest Quarterly Results 

2.83%

6/30/2011

Lowest Quarterly Results

(2.43)%

12/31/2016

The sales charge for Class A shares is not reflected in the returns shown in the bar chart above, and the returns would be less if the charge was taken into account.
Performance Table Heading rr_PerformanceTableHeading Average Annual Total Returns (periods ended 12-31-21)
Performance Table Uses Highest Federal Rate rr_PerformanceTableUsesHighestFederalRate After-tax returns are calculated using the highest historical individual federal marginal income tax rates, and do not reflect state or local income taxes.
Performance Table Not Relevant to Tax Deferred rr_PerformanceTableNotRelevantToTaxDeferred Actual after-tax returns depend on an investor’s own tax situation and may differ from the returns shown, and after-tax returns shown are not relevant to investors who hold their Fund shares through tax-deferred arrangements, such as 401(k) plans or individual retirement accounts.
Performance Table One Class of after Tax Shown [Text] rr_PerformanceTableOneClassOfAfterTaxShown The after-tax returns shown relate only to Class A shares, and after-tax returns for other share classes will vary.
Performance Table Closing [Text Block] rr_PerformanceTableClosingTextBlock

After-tax returns are calculated using the highest historical individual federal marginal income tax rates, and do not reflect state or local income taxes. Actual after-tax returns depend on an investor’s own tax situation and may differ from the returns shown, and after-tax returns shown are not relevant to investors who hold their Fund shares through tax-deferred arrangements, such as 401(k) plans or individual retirement accounts. The after-tax returns shown relate only to Class A shares, and after-tax returns for other share classes will vary.

Retail | Thornburg Limited Term Municipal Fund | Thornburg Limited Term Municipal Fund - Class A  
Prospectus [Line Items] rr_ProspectusLineItems  
Trading Symbol dei_TradingSymbol LTMFX
Maximum Sales Charge Imposed on Purchases (as a percentage of Offering Price) rr_MaximumSalesChargeImposedOnPurchasesOverOfferingPrice 2.25%
Maximum Deferred Sales Charge (as a percentage) rr_MaximumDeferredSalesChargeOverOther none [44]
Management Fees (as a percentage of Assets) rr_ManagementFeesOverAssets 0.27%
Distribution and Service (12b-1) Fees rr_DistributionAndService12b1FeesOverAssets 0.25%
Other Expenses (as a percentage of Assets): rr_OtherExpensesOverAssets 0.17%
Expenses (as a percentage of Assets) rr_ExpensesOverAssets 0.69%
Fee Waiver or Reimbursement rr_FeeWaiverOrReimbursementOverAssets
Net Expenses (as a percentage of Assets) rr_NetExpensesOverAssets 0.69%
Expense Example, with Redemption, 1 Year rr_ExpenseExampleYear01 $ 294
Expense Example, with Redemption, 3 Years rr_ExpenseExampleYear03 441
Expense Example, with Redemption, 5 Years rr_ExpenseExampleYear05 601
Expense Example, with Redemption, 10 Years rr_ExpenseExampleYear10 $ 1,064
Annual Return 2012 rr_AnnualReturn2012 3.07%
Annual Return 2013 rr_AnnualReturn2013 (0.19%)
Annual Return 2014 rr_AnnualReturn2014 2.99%
Annual Return 2015 rr_AnnualReturn2015 1.50%
Annual Return 2016 rr_AnnualReturn2016 (0.69%)
Annual Return 2017 rr_AnnualReturn2017 2.29%
Annual Return 2018 rr_AnnualReturn2018 0.88%
Annual Return 2019 rr_AnnualReturn2019 3.81%
Annual Return 2020 rr_AnnualReturn2020 2.96%
Annual Return 2021 rr_AnnualReturn2021 (0.19%)
Highest Quarterly Return, Label rr_HighestQuarterlyReturnLabel Highest Quarterly Results
Highest Quarterly Return, Date rr_BarChartHighestQuarterlyReturnDate Jun. 30, 2011
Highest Quarterly Return rr_BarChartHighestQuarterlyReturn 2.83%
Lowest Quarterly Return, Label rr_LowestQuarterlyReturnLabel Lowest Quarterly Results
Lowest Quarterly Return, Date rr_BarChartLowestQuarterlyReturnDate Dec. 31, 2016
Lowest Quarterly Return rr_BarChartLowestQuarterlyReturn (2.43%)
1 Year rr_AverageAnnualReturnYear01 (2.45%)
5 Years rr_AverageAnnualReturnYear05 1.63%
10 Years rr_AverageAnnualReturnYear10 1.48%
Retail | Thornburg Limited Term Municipal Fund | Thornburg Limited Term Municipal Fund - Class A | After Taxes on Distributions  
Prospectus [Line Items] rr_ProspectusLineItems  
1 Year rr_AverageAnnualReturnYear01 (2.45%)
5 Years rr_AverageAnnualReturnYear05 1.63%
10 Years rr_AverageAnnualReturnYear10 1.48%
Retail | Thornburg Limited Term Municipal Fund | Thornburg Limited Term Municipal Fund - Class A | After Taxes on Distributions and Sales  
Prospectus [Line Items] rr_ProspectusLineItems  
1 Year rr_AverageAnnualReturnYear01 (0.95%)
5 Years rr_AverageAnnualReturnYear05 1.62%
10 Years rr_AverageAnnualReturnYear10 1.52%
Retail | Thornburg Limited Term Municipal Fund | Thornburg Limited Term Municipal Fund - Class A | ICE BofAML 1-10 Year U.S. Municipal Securities Index (reflects no deduction for fees, expenses, or taxes)  
Prospectus [Line Items] rr_ProspectusLineItems  
1 Year rr_AverageAnnualReturnYear01 0.48%
5 Years rr_AverageAnnualReturnYear05 2.80%
10 Years rr_AverageAnnualReturnYear10 2.28%
Retail | Thornburg Limited Term Municipal Fund | Thornburg Limited Term Municipal Fund - Class C  
Prospectus [Line Items] rr_ProspectusLineItems  
Trading Symbol dei_TradingSymbol LTMCX
Maximum Sales Charge Imposed on Purchases (as a percentage of Offering Price) rr_MaximumSalesChargeImposedOnPurchasesOverOfferingPrice none
Maximum Deferred Sales Charge (as a percentage) rr_MaximumDeferredSalesChargeOverOther 0.50% [45]
Management Fees (as a percentage of Assets) rr_ManagementFeesOverAssets 0.27%
Distribution and Service (12b-1) Fees rr_DistributionAndService12b1FeesOverAssets 0.50%
Other Expenses (as a percentage of Assets): rr_OtherExpensesOverAssets 0.20%
Expenses (as a percentage of Assets) rr_ExpensesOverAssets 0.97%
Fee Waiver or Reimbursement rr_FeeWaiverOrReimbursementOverAssets
Net Expenses (as a percentage of Assets) rr_NetExpensesOverAssets 0.97%
Expense Example, with Redemption, 1 Year rr_ExpenseExampleYear01 $ 149
Expense Example, with Redemption, 3 Years rr_ExpenseExampleYear03 309
Expense Example, with Redemption, 5 Years rr_ExpenseExampleYear05 536
Expense Example, with Redemption, 10 Years rr_ExpenseExampleYear10 1,190
Expense Example, No Redemption, 1 Year rr_ExpenseExampleNoRedemptionYear01 99
Expense Example, No Redemption, 3 Years rr_ExpenseExampleNoRedemptionYear03 309
Expense Example, No Redemption, 5 Years rr_ExpenseExampleNoRedemptionYear05 536
Expense Example, No Redemption, 10 Years rr_ExpenseExampleNoRedemptionYear10 $ 1,190
1 Year rr_AverageAnnualReturnYear01 (0.89%)
5 Years rr_AverageAnnualReturnYear05 1.68%
10 Years rr_AverageAnnualReturnYear10 1.38%
Retail | Thornburg Limited Term Municipal Fund | Thornburg Limited Term Municipal Fund - Class C | ICE BofAML 1-10 Year U.S. Municipal Securities Index (reflects no deduction for fees, expenses, or taxes)  
Prospectus [Line Items] rr_ProspectusLineItems  
1 Year rr_AverageAnnualReturnYear01 0.48%
5 Years rr_AverageAnnualReturnYear05 2.80%
10 Years rr_AverageAnnualReturnYear10 2.28%
Retail | Thornburg Limited Term Municipal Fund | Thornburg Limited Term Municipal Fund - Class C2  
Prospectus [Line Items] rr_ProspectusLineItems  
Trading Symbol dei_TradingSymbol LTMQX
Maximum Sales Charge Imposed on Purchases (as a percentage of Offering Price) rr_MaximumSalesChargeImposedOnPurchasesOverOfferingPrice none
Maximum Deferred Sales Charge (as a percentage) rr_MaximumDeferredSalesChargeOverOther 0.65% [45]
Management Fees (as a percentage of Assets) rr_ManagementFeesOverAssets 0.27%
Distribution and Service (12b-1) Fees rr_DistributionAndService12b1FeesOverAssets 0.65%
Other Expenses (as a percentage of Assets): rr_OtherExpensesOverAssets 0.80%
Expenses (as a percentage of Assets) rr_ExpensesOverAssets 1.72%
Fee Waiver or Reimbursement rr_FeeWaiverOrReimbursementOverAssets (0.48%) [46]
Net Expenses (as a percentage of Assets) rr_NetExpensesOverAssets 1.24%
Expense Example, with Redemption, 1 Year rr_ExpenseExampleYear01 $ 191
Expense Example, with Redemption, 3 Years rr_ExpenseExampleYear03 495
Expense Example, with Redemption, 5 Years rr_ExpenseExampleYear05 888
Expense Example, with Redemption, 10 Years rr_ExpenseExampleYear10 1,990
Expense Example, No Redemption, 1 Year rr_ExpenseExampleNoRedemptionYear01 126
Expense Example, No Redemption, 3 Years rr_ExpenseExampleNoRedemptionYear03 495
Expense Example, No Redemption, 5 Years rr_ExpenseExampleNoRedemptionYear05 888
Expense Example, No Redemption, 10 Years rr_ExpenseExampleNoRedemptionYear10 $ 1,990
1 Year rr_AverageAnnualReturnYear01 (1.39%)
Since Inception rr_AverageAnnualReturnSinceInception (0.22%)
Inception Date rr_AverageAnnualReturnInceptionDate Oct. 01, 2020
Retail | Thornburg Limited Term Municipal Fund | Thornburg Limited Term Municipal Fund - Class C2 | ICE BofAML 1-10 Year U.S. Municipal Securities Index (reflects no deduction for fees, expenses, or taxes)  
Prospectus [Line Items] rr_ProspectusLineItems  
1 Year rr_AverageAnnualReturnYear01 0.48%
Since Inception rr_AverageAnnualReturnSinceInception 1.09%
Retail | Thornburg Limited Term Municipal Fund | Thornburg Limited Term Municipal Fund - Class I  
Prospectus [Line Items] rr_ProspectusLineItems  
Trading Symbol dei_TradingSymbol LTMIX
Maximum Sales Charge Imposed on Purchases (as a percentage of Offering Price) rr_MaximumSalesChargeImposedOnPurchasesOverOfferingPrice none
Maximum Deferred Sales Charge (as a percentage) rr_MaximumDeferredSalesChargeOverOther none
Management Fees (as a percentage of Assets) rr_ManagementFeesOverAssets 0.27%
Distribution and Service (12b-1) Fees rr_DistributionAndService12b1FeesOverAssets none
Other Expenses (as a percentage of Assets): rr_OtherExpensesOverAssets 0.19%
Expenses (as a percentage of Assets) rr_ExpensesOverAssets 0.46%
Fee Waiver or Reimbursement rr_FeeWaiverOrReimbursementOverAssets
Net Expenses (as a percentage of Assets) rr_NetExpensesOverAssets 0.46%
Expense Example, with Redemption, 1 Year rr_ExpenseExampleYear01 $ 47
Expense Example, with Redemption, 3 Years rr_ExpenseExampleYear03 148
Expense Example, with Redemption, 5 Years rr_ExpenseExampleYear05 258
Expense Example, with Redemption, 10 Years rr_ExpenseExampleYear10 $ 579
1 Year rr_AverageAnnualReturnYear01 0.04%
5 Years rr_AverageAnnualReturnYear05 2.20%
10 Years rr_AverageAnnualReturnYear10 1.92%
Retail | Thornburg Limited Term Municipal Fund | Thornburg Limited Term Municipal Fund - Class I | ICE BofAML 1-10 Year U.S. Municipal Securities Index (reflects no deduction for fees, expenses, or taxes)  
Prospectus [Line Items] rr_ProspectusLineItems  
1 Year rr_AverageAnnualReturnYear01 0.48%
5 Years rr_AverageAnnualReturnYear05 2.80%
10 Years rr_AverageAnnualReturnYear10 2.28%
Retail | Thornburg California Limited Term Municipal Fund  
Prospectus [Line Items] rr_ProspectusLineItems  
Risk/Return [Heading] rr_RiskReturnHeading Limited Term California Fund
Objective [Heading] rr_ObjectiveHeading Investment Goal
Objective, Primary [Text Block] rr_ObjectivePrimaryTextBlock

The primary investment goal of Limited Term California Fund is to obtain as high a level of current income exempt from federal and California state individual income taxes as is consistent, in the view of the Fund’s investment advisor, with preservation of capital.
Objective, Secondary [Text Block] rr_ObjectiveSecondaryTextBlock

The secondary goal of the Fund is to reduce expected changes in its share price compared to longer intermediate and long-term bond portfolios.
Expense [Heading] rr_ExpenseHeading Fees and Expenses of the Fund
Expense Narrative [Text Block] rr_ExpenseNarrativeTextBlock

This table describes the fees and expenses that you may pay if you buy and hold shares of the Fund. You may qualify for discounts from the sales charges applicable to Class A shares if you or other qualifying account holders invest, or agree to invest in the future, at least $50,000 in the Thornburg Funds. More information about this and other discounts and sales charge waivers is available from your financial intermediary, in the Prospectus under the captions “Class A Sales Charge Waivers,” beginning on page 146, and “Appendix A – Sales Charge Waivers Offered by Financial Intermediaries,” beginning on page 200, and in the Statement of Additional Information under the caption “Additional Information Respecting Purchase and Redemption of Shares,” beginning on page 108.
Shareholder Fees Caption [Text] rr_ShareholderFeesCaption Shareholder Fees (fees paid directly from your investment)
Operating Expenses Caption [Text] rr_OperatingExpensesCaption Annual Fund Operating Expenses (expenses that you pay each year as a percentage of the value of your investment)
Fee Waiver or Reimbursement over Assets, Date of Termination rr_FeeWaiverOrReimbursementOverAssetsDateOfTermination February 1, 2023
Portfolio Turnover [Heading] rr_PortfolioTurnoverHeading Portfolio Turnover.
Portfolio Turnover [Text Block] rr_PortfolioTurnoverTextBlock

The Fund pays transaction costs, such as commissions, when it buys and sells securities (or “turns over”) its portfolio. A higher portfolio turnover rate may indicate higher transaction costs and may result in higher taxes when Fund shares are held in a taxable account. These costs, which are not reflected in Annual Fund Operating Expenses or in the Example, affect the Fund’s performance. During the most recent fiscal year, the Fund’s portfolio turnover rate was 16.22% of the average value of its portfolio.
Portfolio Turnover, Rate rr_PortfolioTurnoverRate 16.22%
Expense Breakpoint Discounts [Text] rr_ExpenseBreakpointDiscounts You may qualify for discounts from the sales charges applicable to Class A shares if you or other qualifying account holders invest, or agree to invest in the future, at least $50,000 in the Thornburg Funds.
Expense Breakpoint, Minimum Investment Required [Amount] rr_ExpenseBreakpointMinimumInvestmentRequiredAmount $ 50,000
Expense Example [Heading] rr_ExpenseExampleHeading Example.
Expense Example Narrative [Text Block] rr_ExpenseExampleNarrativeTextBlock

This Example is intended to help you compare the cost of investing in the Fund with the cost of investing in other mutual funds.

The Example assumes that you invest $10,000 in the Fund for the time periods indicated and then redeem all of your shares at the end of those periods. The Example also assumes that your investment has a 5% return each year, dividends and distributions are reinvested, and that the Fund’s operating expenses remain the same. Although your actual costs may be higher or lower, based on these assumptions your costs would be:
Expense Example, No Redemption Narrative [Text Block] rr_ExpenseExampleNoRedemptionNarrativeTextBlock

You would pay the following expenses if you did not redeem your Class C shares:
Strategy [Heading] rr_StrategyHeading Principal Investment Strategies
Strategy Narrative [Text Block] rr_StrategyNarrativeTextBlock

The Fund pursues its primary goal by investing principally in a laddered maturity portfolio of municipal obligations issued by the State of California and its agencies, and by California local governments and their agencies. Thornburg Investment Management, Inc. (“Thornburg”) actively manages the Fund’s portfolio. Investment decisions are based upon outlooks for interest rates and securities markets, the supply of municipal debt obligations, and analysis of specific securities. The Fund invests in obligations and participations in obligations which are rated by a nationally recognized statistical rating organization at the time of purchase as investment grade or, if unrated, are issued by obligors which Thornburg determines have comparable investment grade obligations outstanding or which are deemed by Thornburg to be comparable to obligors with outstanding investment grade obligations. “Participations” are undivided interests in pools of securities where the underlying credit support passes through to the participants. The Fund may invest in obligations issued by United States territories and possessions. The Fund’s portfolio is “laddered” by investing in obligations of different maturities so that some obligations mature during each of the coming years.

Because the magnitude of changes in value of interest-bearing obligations is greater for obligations with longer terms given an equivalent change in interest rates, the Fund seeks to reduce changes in its share value by maintaining a portfolio of investments with a dollar-weighted average maturity normally less than five years. As a result, the Fund also maintains a portfolio of investments having a dollar-weighted average effective duration of normally no more than five years. Duration is a measure of estimated sensitivity to interest rate changes. A portfolio with a longer average effective duration will typically be more sensitive to interest rate changes than a portfolio with a shorter average effective duration. Duration is commonly expressed as a number, which is the expected percentage change in an obligation’s price upon a 1% change in interest rates. For example, an obligation with a duration of 5 would be expected to change in price by approximately 5% in response to a 1% change in interest rates. During temporary periods the Fund’s portfolio maturity and average effective duration may be reduced for defensive purposes. There is no limitation on the maturity of any specific security the Fund may purchase. The Fund may dispose of any security before it matures. The Fund also attempts to reduce changes in its share value through credit analysis, selection and diversification.

The Fund ordinarily acquires and holds securities for investment rather than for realization of gains by short-term trading on market fluctuations. However, it may sell an investment prior to its scheduled maturity date to enhance income or reduce loss, to change the portfolio’s average duration or average maturity, to pursue other investment opportunities, in response to changes in the conditions or business of the investment’s issuer or changes in overall market conditions, or if, in Thornburg’s opinion, the investment no longer serves to achieve the Fund’s investment goals.  The objective of preserving capital may prevent the Fund from obtaining the highest yields available.

Under normal conditions the Fund invests at least 80% of its assets in municipal obligations originating in California which are exempt from California and regular federal income taxes, and normally invests 100% of its assets in municipal obligations originating in California or issued by United States territories and possessions and exempt from regular federal income tax. The Fund may invest up to 20% of its assets in taxable securities which would produce income not exempt from federal or California income tax because of market conditions, pending investment of idle funds or to afford liquidity. The Fund’s temporary taxable investments may exceed 20% of its assets when made for defensive purposes during periods of abnormal market conditions. If the Fund found it necessary to own taxable investments, some of its income would be subject to federal and California income taxes.
Risk [Heading] rr_RiskHeading Principal Investment Risks
Risk Narrative [Text Block] rr_RiskNarrativeTextBlock

An investment in the Fund is not a deposit in any bank and is not insured or guaranteed by the Federal Deposit Insurance Corporation or any other government agency. Accordingly, the loss of money is a risk of investing in the Fund. The value of the Fund’s shares and its dividends may fluctuate from day to day and over time, and when you sell your shares they may be worth less than what you paid for them. The following is a summary of the principal risks of investing in the Fund.

Management Risk – The Fund is an actively managed portfolio, and the value of the Fund may be reduced if Thornburg pursues unsuccessful investments or fails to correctly identify risks affecting the broad economy or specific issuers in which the Fund invests.

Interest Rate Risk – When interest rates increase, the value of the Fund’s investments may decline and the Fund’s share value may be reduced. This effect is typically more pronounced for intermediate and longer-term obligations. When interest rates decrease, the Fund’s dividends may decline. Decreases in market interest rates may also result in prepayments of obligations the Fund acquires, requiring the Fund to reinvest at lower interest rates.

Credit Risk – If obligations held by the Fund are downgraded by ratings agencies or go into default, or if legislation or other government action reduces the ability of issuers to pay principal and interest when due, the value of those obligations may decline and the Fund’s share value and the dividends paid by the Fund may be reduced. Lower-rated or unrated obligations held by the Fund may have, or may be perceived to have, greater risk of default and ratings downgrades. For example, municipal leases held by the Fund may be subject to non-appropriation provisions which permit governmental agencies or issuers to discontinue payments to the Fund under the municipal leases.

Market and Economic Risk – The value of the Fund’s investments may decline and its share value may be reduced due to changes in general economic and market conditions. This effect is typically more pronounced for the Fund’s investments in lower-rated and unrated municipal obligations, the value of which may fluctuate more significantly in response to poor economic growth or other changes in market conditions, political, economic and legal developments, and developments affecting specific issuers.

Liquidity Risk – Due to a lack of demand in the marketplace or other factors, the Fund may not be able to sell promptly some or all of the obligations that it holds, or may only be able to sell obligations at less than desired prices. The market for lower-rated and unrated obligations may be less liquid than the market for other obligations, making it difficult for the Fund to value its investment in a lower-rated or unrated obligation or to sell the investment in a timely manner or at an acceptable price.

Single State Risk – Because the Fund invests primarily in obligations originating in California, the Fund’s share value may be more sensitive to adverse economic, political or regulatory developments in that state. Budgetary concerns, decreased revenues, and adverse conditions significant to a sector of the state, municipalities within the state, or local economies may negatively affect the ability of state and local issuers to make full and timely principal or interest payments on their debt obligations.

Cybersecurity and Operational Risk – Operational failures, cyber-attacks or other disruptions that affect the Fund’s service providers, the Fund’s counterparties, other market participants or the issuers of securities held by the Fund may adversely affect the Fund and its shareholders, including by causing losses for the Fund or impairing Fund operations.

Additional information about Fund investments, investment strategies and risks of investing in the Fund appears beginning on page 118 of the Prospectus.
Risk Lose Money [Text] rr_RiskLoseMoney Accordingly, the loss of money is a risk of investing in the Fund.
RIsk Not Insured [Text] rr_RiskNotInsured An investment in the Fund is not a deposit in any bank and is not insured or guaranteed by the Federal Deposit Insurance Corporation or any other government agency.
Bar Chart and Performance Table [Heading] rr_BarChartAndPerformanceTableHeading Past Performance of the Fund
Performance Narrative [Text Block] rr_PerformanceNarrativeTextBlock

The following information provides some indication of the risks of investing in Limited Term California Fund by showing how the Fund’s investment results vary from year to year. The bar chart shows how the annual total returns for Class A shares have been different in each full year shown. The average annual total return figures compare Class A, Class C, Class C2 and Class I share performance to the ICE BofAML 1-10 Year U.S. Municipal Securities Index, a broad measure of market performance. Past performance (before and after taxes) is not necessarily an indication of how the Fund will perform in the future. The performance information shown is as of the calendar year ended December 31, 2021. Updated performance information may be obtained on the Thornburg website at Thornburg.com or by calling 1-800-847-0200.
Performance Information Illustrates Variability of Returns [Text] rr_PerformanceInformationIllustratesVariabilityOfReturns The following information provides some indication of the risks of investing in Limited Term California Fund by showing how the Fund’s investment results vary from year to year.
Performance Availability Phone [Text] rr_PerformanceAvailabilityPhone 1-800-847-0200
Performance Availability Website Address [Text] rr_PerformanceAvailabilityWebSiteAddress Thornburg.com
Performance Past Does Not Indicate Future [Text] rr_PerformancePastDoesNotIndicateFuture Past performance (before and after taxes) is not necessarily an indication of how the Fund will perform in the future.
Bar Chart [Heading] rr_BarChartHeading Annual Total Returns – Class A Shares
Bar Chart Does Not Reflect Sales Loads [Text] rr_BarChartDoesNotReflectSalesLoads The sales charge for Class A shares is not reflected in the returns shown in the bar chart above, and the returns would be less if the charge was taken into account.
Bar Chart Closing [Text Block] rr_BarChartClosingTextBlock

Total
Returns

Quarter
ended

Highest Quarterly Results

3.12%

6/30/2011

Lowest Quarterly Results

(2.70)%

12/31/2016

The sales charge for Class A shares is not reflected in the returns shown in the bar chart above, and the returns would be less if the charge was taken into account.
Performance Table Heading rr_PerformanceTableHeading Average Annual Total Returns (periods ended 12-31-21)
Performance Table Uses Highest Federal Rate rr_PerformanceTableUsesHighestFederalRate After-tax returns are calculated using the highest historical individual federal marginal income tax rates, and do not reflect state or local income taxes.
Performance Table Not Relevant to Tax Deferred rr_PerformanceTableNotRelevantToTaxDeferred Actual after-tax returns depend on an investor’s own tax situation and may differ from the returns shown, and after-tax returns shown are not relevant to investors who hold their Fund shares through tax-deferred arrangements, such as 401(k) plans or individual retirement accounts.
Performance Table One Class of after Tax Shown [Text] rr_PerformanceTableOneClassOfAfterTaxShown The after-tax returns shown relate only to Class A shares, and after-tax returns for other share classes will vary.
Performance Table Closing [Text Block] rr_PerformanceTableClosingTextBlock

After-tax returns are calculated using the highest historical individual federal marginal income tax rates, and do not reflect state or local income taxes. Actual after-tax returns depend on an investor’s own tax situation and may differ from the returns shown, and after-tax returns shown are not relevant to investors who hold their Fund shares through tax-deferred arrangements, such as 401(k) plans or individual retirement accounts. The after-tax returns shown relate only to Class A shares, and after-tax returns for other share classes will vary.

Retail | Thornburg California Limited Term Municipal Fund | Thornburg California Limited Term Municipal Fund - Class A  
Prospectus [Line Items] rr_ProspectusLineItems  
Trading Symbol dei_TradingSymbol LTCAX
Maximum Sales Charge Imposed on Purchases (as a percentage of Offering Price) rr_MaximumSalesChargeImposedOnPurchasesOverOfferingPrice 2.25%
Maximum Deferred Sales Charge (as a percentage) rr_MaximumDeferredSalesChargeOverOther none [47]
Management Fees (as a percentage of Assets) rr_ManagementFeesOverAssets 0.49%
Distribution and Service (12b-1) Fees rr_DistributionAndService12b1FeesOverAssets 0.25%
Other Expenses (as a percentage of Assets): rr_OtherExpensesOverAssets 0.18%
Expenses (as a percentage of Assets) rr_ExpensesOverAssets 0.92%
Fee Waiver or Reimbursement rr_FeeWaiverOrReimbursementOverAssets (0.18%) [48]
Net Expenses (as a percentage of Assets) rr_NetExpensesOverAssets 0.74%
Expense Example, with Redemption, 1 Year rr_ExpenseExampleYear01 $ 299
Expense Example, with Redemption, 3 Years rr_ExpenseExampleYear03 494
Expense Example, with Redemption, 5 Years rr_ExpenseExampleYear05 706
Expense Example, with Redemption, 10 Years rr_ExpenseExampleYear10 $ 1,315
Annual Return 2012 rr_AnnualReturn2012 3.44%
Annual Return 2013 rr_AnnualReturn2013 0.25%
Annual Return 2014 rr_AnnualReturn2014 3.86%
Annual Return 2015 rr_AnnualReturn2015 1.66%
Annual Return 2016 rr_AnnualReturn2016 (0.99%)
Annual Return 2017 rr_AnnualReturn2017 2.05%
Annual Return 2018 rr_AnnualReturn2018 0.52%
Annual Return 2019 rr_AnnualReturn2019 3.20%
Annual Return 2020 rr_AnnualReturn2020 1.91%
Annual Return 2021 rr_AnnualReturn2021 (0.41%)
Highest Quarterly Return, Label rr_HighestQuarterlyReturnLabel Highest Quarterly Results
Highest Quarterly Return, Date rr_BarChartHighestQuarterlyReturnDate Jun. 30, 2011
Highest Quarterly Return rr_BarChartHighestQuarterlyReturn 3.12%
Lowest Quarterly Return, Label rr_LowestQuarterlyReturnLabel Lowest Quarterly Results
Lowest Quarterly Return, Date rr_BarChartLowestQuarterlyReturnDate Dec. 31, 2016
Lowest Quarterly Return rr_BarChartLowestQuarterlyReturn (2.70%)
1 Year rr_AverageAnnualReturnYear01 (2.66%)
5 Years rr_AverageAnnualReturnYear05 1.14%
10 Years rr_AverageAnnualReturnYear10 1.38%
Retail | Thornburg California Limited Term Municipal Fund | Thornburg California Limited Term Municipal Fund - Class A | After Taxes on Distributions  
Prospectus [Line Items] rr_ProspectusLineItems  
1 Year rr_AverageAnnualReturnYear01 (2.66%)
5 Years rr_AverageAnnualReturnYear05 1.14%
10 Years rr_AverageAnnualReturnYear10 1.38%
Retail | Thornburg California Limited Term Municipal Fund | Thornburg California Limited Term Municipal Fund - Class A | After Taxes on Distributions and Sales  
Prospectus [Line Items] rr_ProspectusLineItems  
1 Year rr_AverageAnnualReturnYear01 (1.13%)
5 Years rr_AverageAnnualReturnYear05 1.19%
10 Years rr_AverageAnnualReturnYear10 1.41%
Retail | Thornburg California Limited Term Municipal Fund | Thornburg California Limited Term Municipal Fund - Class A | ICE BofAML 1-10 Year U.S. Municipal Securities Index (reflects no deduction for fees, expenses, or taxes)  
Prospectus [Line Items] rr_ProspectusLineItems  
1 Year rr_AverageAnnualReturnYear01 0.48%
5 Years rr_AverageAnnualReturnYear05 2.80%
10 Years rr_AverageAnnualReturnYear10 2.28%
Retail | Thornburg California Limited Term Municipal Fund | Thornburg California Limited Term Municipal Fund - Class C  
Prospectus [Line Items] rr_ProspectusLineItems  
Trading Symbol dei_TradingSymbol LTCCX
Maximum Sales Charge Imposed on Purchases (as a percentage of Offering Price) rr_MaximumSalesChargeImposedOnPurchasesOverOfferingPrice none
Maximum Deferred Sales Charge (as a percentage) rr_MaximumDeferredSalesChargeOverOther 0.50% [49]
Management Fees (as a percentage of Assets) rr_ManagementFeesOverAssets 0.49%
Distribution and Service (12b-1) Fees rr_DistributionAndService12b1FeesOverAssets 0.50%
Other Expenses (as a percentage of Assets): rr_OtherExpensesOverAssets 0.28%
Expenses (as a percentage of Assets) rr_ExpensesOverAssets 1.27%
Fee Waiver or Reimbursement rr_FeeWaiverOrReimbursementOverAssets (0.25%) [48]
Net Expenses (as a percentage of Assets) rr_NetExpensesOverAssets 1.02%
Expense Example, with Redemption, 1 Year rr_ExpenseExampleYear01 $ 154
Expense Example, with Redemption, 3 Years rr_ExpenseExampleYear03 378
Expense Example, with Redemption, 5 Years rr_ExpenseExampleYear05 673
Expense Example, with Redemption, 10 Years rr_ExpenseExampleYear10 1,512
Expense Example, No Redemption, 1 Year rr_ExpenseExampleNoRedemptionYear01 104
Expense Example, No Redemption, 3 Years rr_ExpenseExampleNoRedemptionYear03 378
Expense Example, No Redemption, 5 Years rr_ExpenseExampleNoRedemptionYear05 673
Expense Example, No Redemption, 10 Years rr_ExpenseExampleNoRedemptionYear10 $ 1,512
1 Year rr_AverageAnnualReturnYear01 (1.18%)
5 Years rr_AverageAnnualReturnYear05 1.17%
10 Years rr_AverageAnnualReturnYear10 1.27%
Retail | Thornburg California Limited Term Municipal Fund | Thornburg California Limited Term Municipal Fund - Class C | ICE BofAML 1-10 Year U.S. Municipal Securities Index (reflects no deduction for fees, expenses, or taxes)  
Prospectus [Line Items] rr_ProspectusLineItems  
1 Year rr_AverageAnnualReturnYear01 0.48%
5 Years rr_AverageAnnualReturnYear05 2.80%
10 Years rr_AverageAnnualReturnYear10 2.28%
Retail | Thornburg California Limited Term Municipal Fund | Thornburg California Limited Term Municipal Fund - Class C2  
Prospectus [Line Items] rr_ProspectusLineItems  
Trading Symbol dei_TradingSymbol LTCQX
Maximum Sales Charge Imposed on Purchases (as a percentage of Offering Price) rr_MaximumSalesChargeImposedOnPurchasesOverOfferingPrice none
Maximum Deferred Sales Charge (as a percentage) rr_MaximumDeferredSalesChargeOverOther 0.65% [49]
Management Fees (as a percentage of Assets) rr_ManagementFeesOverAssets 0.49%
Distribution and Service (12b-1) Fees rr_DistributionAndService12b1FeesOverAssets 0.65%
Other Expenses (as a percentage of Assets): rr_OtherExpensesOverAssets 5.36%
Expenses (as a percentage of Assets) rr_ExpensesOverAssets 6.50%
Fee Waiver or Reimbursement rr_FeeWaiverOrReimbursementOverAssets (5.48%) [48]
Net Expenses (as a percentage of Assets) rr_NetExpensesOverAssets 1.02%
Expense Example, with Redemption, 1 Year rr_ExpenseExampleYear01 $ 169
Expense Example, with Redemption, 3 Years rr_ExpenseExampleYear03 1,436
Expense Example, with Redemption, 5 Years rr_ExpenseExampleYear05 2,727
Expense Example, with Redemption, 10 Years rr_ExpenseExampleYear10 5,791
Expense Example, No Redemption, 1 Year rr_ExpenseExampleNoRedemptionYear01 104
Expense Example, No Redemption, 3 Years rr_ExpenseExampleNoRedemptionYear03 1,436
Expense Example, No Redemption, 5 Years rr_ExpenseExampleNoRedemptionYear05 2,727
Expense Example, No Redemption, 10 Years rr_ExpenseExampleNoRedemptionYear10 $ 5,791
1 Year rr_AverageAnnualReturnYear01 (1.33%)
Since Inception rr_AverageAnnualReturnSinceInception (0.28%)
Inception Date rr_AverageAnnualReturnInceptionDate Oct. 01, 2020
Retail | Thornburg California Limited Term Municipal Fund | Thornburg California Limited Term Municipal Fund - Class C2 | ICE BofAML 1-10 Year U.S. Municipal Securities Index (reflects no deduction for fees, expenses, or taxes)  
Prospectus [Line Items] rr_ProspectusLineItems  
1 Year rr_AverageAnnualReturnYear01 0.48%
Since Inception rr_AverageAnnualReturnSinceInception 1.09%
Retail | Thornburg California Limited Term Municipal Fund | Thornburg California Limited Term Municipal Fund - Class I  
Prospectus [Line Items] rr_ProspectusLineItems  
Trading Symbol dei_TradingSymbol LTCIX
Maximum Sales Charge Imposed on Purchases (as a percentage of Offering Price) rr_MaximumSalesChargeImposedOnPurchasesOverOfferingPrice none
Maximum Deferred Sales Charge (as a percentage) rr_MaximumDeferredSalesChargeOverOther none
Management Fees (as a percentage of Assets) rr_ManagementFeesOverAssets 0.49%
Distribution and Service (12b-1) Fees rr_DistributionAndService12b1FeesOverAssets none
Other Expenses (as a percentage of Assets): rr_OtherExpensesOverAssets 0.21%
Expenses (as a percentage of Assets) rr_ExpensesOverAssets 0.70%
Fee Waiver or Reimbursement rr_FeeWaiverOrReimbursementOverAssets (0.21%) [48]
Net Expenses (as a percentage of Assets) rr_NetExpensesOverAssets 0.49%
Expense Example, with Redemption, 1 Year rr_ExpenseExampleYear01 $ 50
Expense Example, with Redemption, 3 Years rr_ExpenseExampleYear03 203
Expense Example, with Redemption, 5 Years rr_ExpenseExampleYear05 369
Expense Example, with Redemption, 10 Years rr_ExpenseExampleYear10 $ 851
1 Year rr_AverageAnnualReturnYear01 (0.23%)
5 Years rr_AverageAnnualReturnYear05 1.71%
10 Years rr_AverageAnnualReturnYear10 1.83%
Retail | Thornburg California Limited Term Municipal Fund | Thornburg California Limited Term Municipal Fund - Class I | ICE BofAML 1-10 Year U.S. Municipal Securities Index (reflects no deduction for fees, expenses, or taxes)  
Prospectus [Line Items] rr_ProspectusLineItems  
1 Year rr_AverageAnnualReturnYear01 0.48%
5 Years rr_AverageAnnualReturnYear05 2.80%
10 Years rr_AverageAnnualReturnYear10 2.28%
Retail | Thornburg New Mexico Intermediate Municipal Fund  
Prospectus [Line Items] rr_ProspectusLineItems  
Risk/Return [Heading] rr_RiskReturnHeading Intermediate New Mexico Fund
Objective [Heading] rr_ObjectiveHeading Investment Goal
Objective, Primary [Text Block] rr_ObjectivePrimaryTextBlock

The primary investment goal of Intermediate New Mexico Fund is to obtain as high a level of current income exempt from federal and New Mexico state individual income taxes as is consistent, in the view of the Fund’s investment advisor, with preservation of capital.
Objective, Secondary [Text Block] rr_ObjectiveSecondaryTextBlock

The secondary goal of the Fund is to reduce expected changes in its share price compared to long-term bond portfolios.
Expense [Heading] rr_ExpenseHeading Fees and Expenses of the Fund
Expense Narrative [Text Block] rr_ExpenseNarrativeTextBlock

This table describes the fees and expenses that you may pay if you buy and hold shares of the Fund. You may qualify for discounts from the sales charges applicable to Class A shares if you or other qualifying account holders invest, or agree to invest in the future, at least $50,000 in the Thornburg Funds. More information about this and other discounts and sales charge waivers is available from your financial intermediary, in the Prospectus under the captions “Class A Sales Charge Waivers,” beginning on page 146, and “Appendix A – Sales Charge Waivers Offered by Financial Intermediaries,” beginning on page 200, and in the Statement of Additional Information under the caption “Additional Information Respecting Purchase and Redemption of Shares,” beginning on page 108.
Shareholder Fees Caption [Text] rr_ShareholderFeesCaption Shareholder Fees (fees paid directly from your investment)
Operating Expenses Caption [Text] rr_OperatingExpensesCaption Annual Fund Operating Expenses (expenses that you pay each year as a percentage of the value of your investment)
Fee Waiver or Reimbursement over Assets, Date of Termination rr_FeeWaiverOrReimbursementOverAssetsDateOfTermination February 1, 2023
Portfolio Turnover [Heading] rr_PortfolioTurnoverHeading Portfolio Turnover.
Portfolio Turnover [Text Block] rr_PortfolioTurnoverTextBlock

The Fund pays transaction costs, such as commissions, when it buys and sells securities (or “turns over”) its portfolio. A higher portfolio turnover rate may indicate higher transaction costs and may result in higher taxes when Fund shares are held in a taxable account. These costs, which are not reflected in Annual Fund Operating Expenses or in the Example, affect the Fund’s performance. During the most recent fiscal year, the Fund’s portfolio turnover rate was 7.43% of the average value of its portfolio.

Portfolio Turnover, Rate rr_PortfolioTurnoverRate 7.43%
Expense Breakpoint Discounts [Text] rr_ExpenseBreakpointDiscounts You may qualify for discounts from the sales charges applicable to Class A shares if you or other qualifying account holders invest, or agree to invest in the future, at least $50,000 in the Thornburg Funds.
Expense Breakpoint, Minimum Investment Required [Amount] rr_ExpenseBreakpointMinimumInvestmentRequiredAmount $ 50,000
Expense Example [Heading] rr_ExpenseExampleHeading Example.
Expense Example Narrative [Text Block] rr_ExpenseExampleNarrativeTextBlock

This Example is intended to help you compare the cost of investing in the Fund with the cost of investing in other mutual funds.

The Example assumes that you invest $10,000 in the Fund for the time periods indicated and then redeem all of your shares at the end of those periods. The Example also assumes that your investment has a 5% return each year, dividends and distributions are reinvested, and that the Fund’s operating expenses remain the same. Although your actual costs may be higher or lower, based on these assumptions (and giving effect to fee waivers and expense reimbursements in the first year) your costs would be:
Strategy [Heading] rr_StrategyHeading Principal Investment Strategies
Strategy Narrative [Text Block] rr_StrategyNarrativeTextBlock

The Fund pursues its primary goal by investing principally in a laddered maturity portfolio of municipal obligations issued by the State of New Mexico and its agencies, and by New Mexico local governments and their agencies. Thornburg Investment Management, Inc. (“Thornburg”) actively manages the Fund’s portfolio. Investment decisions are based upon outlooks for interest rates and securities markets, the supply of municipal debt obligations, and analysis of specific securities. The Fund invests in obligations and participations in obligations which are rated by a nationally recognized statistical rating organization at the time of purchase as investment grade or, if unrated, are issued by obligors which Thornburg determines have comparable investment grade obligations outstanding or which are deemed by Thornburg to be comparable to obligors with outstanding investment grade obligations. “Participations” are undivided interests in pools of securities where the underlying credit support passes through to the participants. The Fund may invest in obligations issued by United States territories and possessions. The Fund’s portfolio is “laddered” by investing in obligations of different maturities so that some obligations mature during each of the coming years.

Because the magnitude of changes in value of interest-bearing obligations is greater for obligations with longer terms given an equivalent change in interest rates, the Fund seeks to reduce changes in its share value by maintaining a portfolio of investments with a dollar-weighted average maturity of normally three to ten years. As a result, the Fund also maintains a portfolio of investments having a dollar-weighted average effective duration of normally no more than ten years. Duration is a measure of estimated sensitivity to interest rate changes. A portfolio with a longer average effective duration will typically be more sensitive to interest rate changes than a portfolio with a shorter average effective duration. Duration is commonly expressed as a number, which is the expected percentage change in an obligation’s price upon a 1% change in interest rates. For example, an obligation with a duration of 10 would be expected to change in price by approximately 10% in response to a 1% change in interest rates. During temporary periods the Fund’s portfolio maturity and average effective duration may be reduced for defensive purposes. There is no limitation on the maturity of any specific security the Fund may purchase. The Fund may dispose of any security before it matures. The Fund also attempts to reduce changes in its share value through credit analysis, selection and diversification.

The Fund ordinarily acquires and holds securities for investment rather than for realization of gains by short-term trading on market fluctuations. However, it may sell an investment prior to its scheduled maturity date to enhance income or reduce loss, to change the portfolio’s average duration or average maturity, to pursue other investment opportunities, in response to changes in the conditions or business of the investment’s issuer or changes in overall market conditions, or if, in Thornburg’s opinion, the investment no longer serves to achieve the Fund’s investment goals.  The objective of preserving capital may prevent the Fund from obtaining the highest yields available.

Under normal conditions the Fund invests at least 80% of its assets in municipal obligations originating in New Mexico which are exempt from New Mexico and regular federal income taxes, and normally invests 100% of its assets in municipal obligations originating in New Mexico or issued by United States territories or possessions and exempt from regular federal income tax. The Fund may invest up to 20% of its assets in taxable securities which produce income not exempt from federal or New Mexico income tax because of market conditions, pending investment of idle funds or to afford liquidity. The

Fund’s temporary taxable investments may exceed 20% of its assets when made for defensive purposes during periods of abnormal market conditions. If the Fund found it necessary to own taxable investments, some of the Fund’s income would be subject to federal and New Mexico income taxes.
Risk [Heading] rr_RiskHeading Principal Investment Risks
Risk Narrative [Text Block] rr_RiskNarrativeTextBlock

An investment in the Fund is not a deposit in any bank and is not insured or guaranteed by the Federal Deposit Insurance Corporation or any other government agency. Accordingly, the loss of money is a risk of investing in the Fund. The value of the Fund’s shares and its dividends may fluctuate from day to day and over time, and when you sell your shares they may be worth less than what you paid for them. The following is a summary of the principal risks of investing in the Fund.

Management Risk – The Fund is an actively managed portfolio, and the value of the Fund may be reduced if Thornburg pursues unsuccessful investments or fails to correctly identify risks affecting the broad economy or specific issuers in which the Fund invests.

Interest Rate Risk – When interest rates increase, the value of the Fund’s investments may decline and the Fund’s share value may be reduced. This effect is typically more pronounced for intermediate and longer-term obligations. When interest rates decrease, the Fund’s dividends may decline. Decreases in market interest rates may also result in prepayments of obligations the Fund acquires, requiring the Fund to reinvest at lower interest rates.

Credit Risk – If obligations held by the Fund are downgraded by ratings agencies or go into default, or if legislation or other government action reduces the ability of issuers to pay principal and interest when due, the value of those obligations may decline and the Fund’s share value and the dividends paid by the Fund may be reduced. Lower-rated or unrated obligations held by the Fund may have, or may be perceived to have, greater risk of default and ratings downgrades. For example, municipal leases held by the Fund may be subject to non-appropriation provisions which permit governmental agencies or issuers to discontinue payments to the Fund under the municipal leases.

Market and Economic Risk – The value of the Fund’s investments may decline and its share value may be reduced due to changes in general economic and market conditions. This effect is typically more pronounced for the Fund’s investments in lower-rated and unrated municipal obligations, the value of which may fluctuate more significantly in response to poor economic growth or other changes in market conditions, political, economic and legal developments, and developments affecting specific issuers.

Liquidity Risk – Due to a lack of demand in the marketplace or other factors, the Fund may not be able to sell promptly some or all of the obligations that it holds, or may only be able to sell obligations at less than desired prices. The market for lower-rated and unrated obligations may be less liquid than the market for other obligations, making it difficult for the Fund to value its investment in a lower-rated or unrated obligation or to sell the investment in a timely manner or at an acceptable price.

Single State Risk – Because the Fund invests primarily in obligations originating in New Mexico, the Fund’s share value may be more sensitive to adverse economic, political or regulatory developments in that state. Budgetary concerns, decreased revenues, and adverse conditions significant to a sector of the state, municipalities within the state, or local economies may negatively affect the ability of state and local issuers to make full and timely principal or interest payments on their debt obligations.

Non-diversification Risk – The Fund is a non-diversified investment company, which means that it may invest a greater proportion of its assets in the securities of a single issuer. This may be riskier, because a default or other adverse condition affecting such an issuer could cause the Fund’s share price to decline to a greater degree.

Cybersecurity and Operational Risk – Operational failures, cyber-attacks or other disruptions that affect the Fund’s service providers, the Fund’s counterparties, other market participants or the issuers of securities held by the Fund may adversely affect the Fund and its shareholders, including by causing losses for the Fund or impairing Fund operations.

Additional information about Fund investments, investment strategies and risks of investing in the Fund appears beginning on page 118 of the Prospectus.
Risk Lose Money [Text] rr_RiskLoseMoney Accordingly, the loss of money is a risk of investing in the Fund.
RIsk Not Insured [Text] rr_RiskNotInsured An investment in the Fund is not a deposit in any bank and is not insured or guaranteed by the Federal Deposit Insurance Corporation or any other government agency.
Risk Nondiversified Status [Text] rr_RiskNondiversifiedStatus The Fund is a non-diversified investment company, which means that it may invest a greater proportion of its assets in the securities of a single issuer.
Bar Chart and Performance Table [Heading] rr_BarChartAndPerformanceTableHeading Past Performance of the Fund
Performance Narrative [Text Block] rr_PerformanceNarrativeTextBlock

The following information provides some indication of the risks of investing in Intermediate New Mexico Fund by showing how the Fund’s investment results vary from year to year. The bar chart shows how the annual total returns for Class A shares have been different in each full year shown. The average annual total return figures compare Class A, Class D and Class I share performance to the ICE BofAML 3-15 Year U.S. Municipal Securities Index, a broad measure of market performance. Past performance (before and after taxes) is not necessarily an indication of how the Fund will perform in the future. The performance information shown is as of the calendar year ended December 31, 2021. Updated performance information may be obtained on the Thornburg website at Thornburg.com or by calling 1-800-847-0200.
Performance Information Illustrates Variability of Returns [Text] rr_PerformanceInformationIllustratesVariabilityOfReturns The following information provides some indication of the risks of investing in Intermediate New Mexico Fund by showing how the Fund’s investment results vary from year to year.
Performance Availability Phone [Text] rr_PerformanceAvailabilityPhone 1-800-847-0200
Performance Availability Website Address [Text] rr_PerformanceAvailabilityWebSiteAddress Thornburg.com
Performance Past Does Not Indicate Future [Text] rr_PerformancePastDoesNotIndicateFuture Past performance (before and after taxes) is not necessarily an indication of how the Fund will perform in the future.
Bar Chart [Heading] rr_BarChartHeading Annual Total Returns – Class A Shares
Bar Chart Does Not Reflect Sales Loads [Text] rr_BarChartDoesNotReflectSalesLoads The sales charge for Class A shares is not reflected in the returns shown in the bar chart above, and the returns would be less if the charge was taken into account.
Bar Chart Closing [Text Block] rr_BarChartClosingTextBlock

Total
Returns

Quarter
ended

Highest Quarterly Results

2.83%

6/30/2011

Lowest Quarterly Results

(2.52)%

12/31/2016

The sales charge for Class A shares is not reflected in the returns shown in the bar chart above, and the returns would be less if the charge was taken into account.
Performance Table Heading rr_PerformanceTableHeading Average Annual Total Returns (periods ended 12-31-21)
Performance Table Uses Highest Federal Rate rr_PerformanceTableUsesHighestFederalRate After-tax returns are calculated using the highest historical individual federal marginal income tax rates, and do not reflect state or local income taxes.
Performance Table Not Relevant to Tax Deferred rr_PerformanceTableNotRelevantToTaxDeferred Actual after-tax returns depend on an investor’s own tax situation and may differ from the returns shown, and after-tax returns shown are not relevant to investors who hold their Fund shares through tax-deferred arrangements, such as 401(k) plans or individual retirement accounts.
Performance Table One Class of after Tax Shown [Text] rr_PerformanceTableOneClassOfAfterTaxShown The after-tax returns shown relate only to Class A shares, and after-tax returns for other share classes will vary.
Performance Table Closing [Text Block] rr_PerformanceTableClosingTextBlock

After-tax returns are calculated using the highest historical individual federal marginal income tax rates, and do not reflect state or local income taxes. Actual after-tax returns depend on an investor’s own tax situation and may differ from the returns shown, and after-tax returns shown are not relevant to investors who hold their Fund shares through tax-deferred arrangements, such as 401(k) plans or individual retirement accounts. The after-tax returns shown relate only to Class A shares, and after-tax returns for other share classes will vary.
Retail | Thornburg New Mexico Intermediate Municipal Fund | Thornburg New Mexico Intermediate Municipal Fund - Class A  
Prospectus [Line Items] rr_ProspectusLineItems  
Trading Symbol dei_TradingSymbol THNMX
Maximum Sales Charge Imposed on Purchases (as a percentage of Offering Price) rr_MaximumSalesChargeImposedOnPurchasesOverOfferingPrice 2.00%
Maximum Deferred Sales Charge (as a percentage) rr_MaximumDeferredSalesChargeOverOther none [50]
Management Fees (as a percentage of Assets) rr_ManagementFeesOverAssets 0.50%
Distribution and Service (12b-1) Fees rr_DistributionAndService12b1FeesOverAssets 0.25%
Other Expenses (as a percentage of Assets): rr_OtherExpensesOverAssets 0.23%
Expenses (as a percentage of Assets) rr_ExpensesOverAssets 0.98%
Fee Waiver or Reimbursement rr_FeeWaiverOrReimbursementOverAssets
Net Expenses (as a percentage of Assets) rr_NetExpensesOverAssets 0.98%
Expense Example, with Redemption, 1 Year rr_ExpenseExampleYear01 $ 298
Expense Example, with Redemption, 3 Years rr_ExpenseExampleYear03 506
Expense Example, with Redemption, 5 Years rr_ExpenseExampleYear05 731
Expense Example, with Redemption, 10 Years rr_ExpenseExampleYear10 $ 1,377
Annual Return 2012 rr_AnnualReturn2012 3.31%
Annual Return 2013 rr_AnnualReturn2013 (1.64%)
Annual Return 2014 rr_AnnualReturn2014 5.57%
Annual Return 2015 rr_AnnualReturn2015 2.16%
Annual Return 2016 rr_AnnualReturn2016 (0.41%)
Annual Return 2017 rr_AnnualReturn2017 2.03%
Annual Return 2018 rr_AnnualReturn2018 1.40%
Annual Return 2019 rr_AnnualReturn2019 4.49%
Annual Return 2020 rr_AnnualReturn2020 3.46%
Annual Return 2021 rr_AnnualReturn2021 0.10%
Highest Quarterly Return, Label rr_HighestQuarterlyReturnLabel Highest Quarterly Results
Highest Quarterly Return, Date rr_BarChartHighestQuarterlyReturnDate Jun. 30, 2011
Highest Quarterly Return rr_BarChartHighestQuarterlyReturn 2.83%
Lowest Quarterly Return, Label rr_LowestQuarterlyReturnLabel Lowest Quarterly Results
Lowest Quarterly Return, Date rr_BarChartLowestQuarterlyReturnDate Dec. 31, 2016
Lowest Quarterly Return rr_BarChartLowestQuarterlyReturn (2.52%)
1 Year rr_AverageAnnualReturnYear01 (1.93%)
5 Years rr_AverageAnnualReturnYear05 1.87%
10 Years rr_AverageAnnualReturnYear10 1.82%
Retail | Thornburg New Mexico Intermediate Municipal Fund | Thornburg New Mexico Intermediate Municipal Fund - Class A | After Taxes on Distributions  
Prospectus [Line Items] rr_ProspectusLineItems  
1 Year rr_AverageAnnualReturnYear01 (1.93%)
5 Years rr_AverageAnnualReturnYear05 1.87%
10 Years rr_AverageAnnualReturnYear10 1.82%
Retail | Thornburg New Mexico Intermediate Municipal Fund | Thornburg New Mexico Intermediate Municipal Fund - Class A | After Taxes on Distributions and Sales  
Prospectus [Line Items] rr_ProspectusLineItems  
1 Year rr_AverageAnnualReturnYear01 (0.57%)
5 Years rr_AverageAnnualReturnYear05 1.91%
10 Years rr_AverageAnnualReturnYear10 1.93%
Retail | Thornburg New Mexico Intermediate Municipal Fund | Thornburg New Mexico Intermediate Municipal Fund - Class A | ICE BofAML 3-15 Year U.S. Municipal Securities Index (reflects no deduction for fees, expenses, or taxes)  
Prospectus [Line Items] rr_ProspectusLineItems  
1 Year rr_AverageAnnualReturnYear01 0.94%
5 Years rr_AverageAnnualReturnYear05 3.77%
10 Years rr_AverageAnnualReturnYear10 3.22%
Retail | Thornburg New Mexico Intermediate Municipal Fund | Thornburg New Mexico Intermediate Municipal Fund - Class D  
Prospectus [Line Items] rr_ProspectusLineItems  
Trading Symbol dei_TradingSymbol THNDX
Maximum Sales Charge Imposed on Purchases (as a percentage of Offering Price) rr_MaximumSalesChargeImposedOnPurchasesOverOfferingPrice none
Maximum Deferred Sales Charge (as a percentage) rr_MaximumDeferredSalesChargeOverOther none
Management Fees (as a percentage of Assets) rr_ManagementFeesOverAssets 0.50%
Distribution and Service (12b-1) Fees rr_DistributionAndService12b1FeesOverAssets 0.50%
Other Expenses (as a percentage of Assets): rr_OtherExpensesOverAssets 0.29%
Expenses (as a percentage of Assets) rr_ExpensesOverAssets 1.29%
Fee Waiver or Reimbursement rr_FeeWaiverOrReimbursementOverAssets (0.05%) [51]
Net Expenses (as a percentage of Assets) rr_NetExpensesOverAssets 1.24%
Expense Example, with Redemption, 1 Year rr_ExpenseExampleYear01 $ 126
Expense Example, with Redemption, 3 Years rr_ExpenseExampleYear03 404
Expense Example, with Redemption, 5 Years rr_ExpenseExampleYear05 703
Expense Example, with Redemption, 10 Years rr_ExpenseExampleYear10 $ 1,552
1 Year rr_AverageAnnualReturnYear01 (0.23%)
5 Years rr_AverageAnnualReturnYear05 2.01%
10 Years rr_AverageAnnualReturnYear10 1.77%
Retail | Thornburg New Mexico Intermediate Municipal Fund | Thornburg New Mexico Intermediate Municipal Fund - Class D | ICE BofAML 3-15 Year U.S. Municipal Securities Index (reflects no deduction for fees, expenses, or taxes)  
Prospectus [Line Items] rr_ProspectusLineItems  
1 Year rr_AverageAnnualReturnYear01 0.94%
5 Years rr_AverageAnnualReturnYear05 3.77%
10 Years rr_AverageAnnualReturnYear10 3.22%
Retail | Thornburg New Mexico Intermediate Municipal Fund | Thornburg New Mexico Intermediate Municipal Fund - Class I  
Prospectus [Line Items] rr_ProspectusLineItems  
Trading Symbol dei_TradingSymbol THNIX
Maximum Sales Charge Imposed on Purchases (as a percentage of Offering Price) rr_MaximumSalesChargeImposedOnPurchasesOverOfferingPrice none
Maximum Deferred Sales Charge (as a percentage) rr_MaximumDeferredSalesChargeOverOther none
Management Fees (as a percentage of Assets) rr_ManagementFeesOverAssets 0.50%
Distribution and Service (12b-1) Fees rr_DistributionAndService12b1FeesOverAssets none
Other Expenses (as a percentage of Assets): rr_OtherExpensesOverAssets 0.21%
Expenses (as a percentage of Assets) rr_ExpensesOverAssets 0.71%
Fee Waiver or Reimbursement rr_FeeWaiverOrReimbursementOverAssets (0.04%) [51]
Net Expenses (as a percentage of Assets) rr_NetExpensesOverAssets 0.67%
Expense Example, with Redemption, 1 Year rr_ExpenseExampleYear01 $ 68
Expense Example, with Redemption, 3 Years rr_ExpenseExampleYear03 223
Expense Example, with Redemption, 5 Years rr_ExpenseExampleYear05 391
Expense Example, with Redemption, 10 Years rr_ExpenseExampleYear10 $ 879
1 Year rr_AverageAnnualReturnYear01 0.34%
5 Years rr_AverageAnnualReturnYear05 2.59%
10 Years rr_AverageAnnualReturnYear10 2.35%
Retail | Thornburg New Mexico Intermediate Municipal Fund | Thornburg New Mexico Intermediate Municipal Fund - Class I | ICE BofAML 3-15 Year U.S. Municipal Securities Index (reflects no deduction for fees, expenses, or taxes)  
Prospectus [Line Items] rr_ProspectusLineItems  
1 Year rr_AverageAnnualReturnYear01 0.94%
5 Years rr_AverageAnnualReturnYear05 3.77%
10 Years rr_AverageAnnualReturnYear10 3.22%
Retail | Thornburg New York Intermediate Municipal Fund  
Prospectus [Line Items] rr_ProspectusLineItems  
Risk/Return [Heading] rr_RiskReturnHeading Intermediate New York Fund
Objective [Heading] rr_ObjectiveHeading Investment Goal
Objective, Primary [Text Block] rr_ObjectivePrimaryTextBlock

The primary investment goal of Intermediate New York Fund is to obtain as high a level of current income exempt from federal, New York State and New York City individual income taxes as is consistent, in the view of the Fund’s investment advisor, with preservation of capital.
Objective, Secondary [Text Block] rr_ObjectiveSecondaryTextBlock

The secondary goal of the Fund is to reduce expected changes in its share price compared to long-term bond portfolios.
Expense [Heading] rr_ExpenseHeading Fees and Expenses of the Fund
Expense Narrative [Text Block] rr_ExpenseNarrativeTextBlock

This table describes the fees and expenses that you may pay if you buy and hold shares of the Fund. You may qualify for discounts from the sales charges applicable to Class A shares if you or other qualifying account holders invest, or agree to invest in the future, at least $50,000 in the Thornburg Funds. More information about this and other discounts and sales charge waivers is available from your financial intermediary, in the Prospectus under the captions “Class A Sales Charge Waivers,” beginning on page 146, and “Appendix A – Sales Charge Waivers Offered by Financial Intermediaries,” beginning on page 200, and in the Statement of Additional Information under the caption “Additional Information Respecting Purchase and Redemption of Shares,” beginning on page 108.
Shareholder Fees Caption [Text] rr_ShareholderFeesCaption Shareholder Fees (fees paid directly from your investment)
Operating Expenses Caption [Text] rr_OperatingExpensesCaption Annual Fund Operating Expenses (expenses that you pay each year as a percentage of the value of your investment)
Fee Waiver or Reimbursement over Assets, Date of Termination rr_FeeWaiverOrReimbursementOverAssetsDateOfTermination February 1, 2023
Portfolio Turnover [Heading] rr_PortfolioTurnoverHeading Portfolio Turnover.
Portfolio Turnover [Text Block] rr_PortfolioTurnoverTextBlock

The Fund pays transaction costs, such as commissions, when it buys and sells securities (or “turns over”) its portfolio. A higher portfolio turnover rate may indicate higher transaction costs and may result in higher taxes when Fund shares are held in a taxable account. These costs, which are not reflected in Annual Fund Operating Expenses or in the Example, affect the Fund’s performance. During the most recent fiscal year, the Fund’s portfolio turnover rate was 11.29% of the average value of its portfolio.
Portfolio Turnover, Rate rr_PortfolioTurnoverRate 11.29%
Expense Breakpoint Discounts [Text] rr_ExpenseBreakpointDiscounts You may qualify for discounts from the sales charges applicable to Class A shares if you or other qualifying account holders invest, or agree to invest in the future, at least $50,000 in the Thornburg Funds.
Expense Breakpoint, Minimum Investment Required [Amount] rr_ExpenseBreakpointMinimumInvestmentRequiredAmount $ 50,000
Expense Example [Heading] rr_ExpenseExampleHeading Example.
Expense Example Narrative [Text Block] rr_ExpenseExampleNarrativeTextBlock

This Example is intended to help you compare the cost of investing in the Fund with the cost of investing in other mutual funds.

The Example assumes that you invest $10,000 in the Fund for the time periods indicated and then redeem all of your shares at the end of those periods. The Example also assumes that your investment has a 5% return each year, dividends and distributions are reinvested, and that the Fund’s operating expenses remain the same. Although your actual costs may be higher or lower, based on these assumptions (and giving effect to fee waivers and expense reimbursements in the first year), your costs would be:
Strategy [Heading] rr_StrategyHeading Principal Investment Strategies
Strategy Narrative [Text Block] rr_StrategyNarrativeTextBlock

The Fund pursues its primary goal by investing principally in a laddered maturity portfolio of municipal obligations issued by New York State and its agencies, and by New York State local governments and their agencies. Thornburg Investment Management, Inc. (“Thornburg”) actively manages the Fund’s portfolio. Investment decisions are based upon outlooks for interest rates and securities markets, the supply of municipal debt obligations, and analysis of specific securities. The Fund invests in obligations and participations in obligations which are rated by a nationally recognized statistical rating organization at the time of purchase as investment grade or, if unrated, are issued by obligors which Thornburg determines have comparable investment grade obligations outstanding or which are deemed by Thornburg to be comparable to obligors with outstanding investment grade obligations. “Participations” are undivided interests in pools of securities where the underlying credit support passes through to the participants. The Fund may invest in obligations issued by United States territories and possessions. The Fund’s portfolio is “laddered” by investing in obligations of different maturities so that some obligations mature during each of the coming years.

Because the magnitude of changes in value of interest-bearing obligations is greater for obligations with longer terms given an equivalent change in interest rates, the Fund seeks to reduce changes in its share value by maintaining a portfolio of investments with a dollar-weighted average maturity of normally three to ten years. As a result, the Fund also maintains a portfolio of investments having a dollar-weighted average effective duration of normally no more than ten years. Duration is a measure of estimated sensitivity to interest rate changes. A portfolio with a longer average effective duration will typically be more sensitive to interest rate changes than a portfolio with a shorter average effective duration. Duration is commonly expressed as a number, which is the expected percentage change in an obligation’s price upon a 1% change in interest rates. For example, an obligation with a duration of 10 would be expected to change in price by approximately 10% in response to a 1% change in interest rates. During temporary periods the Fund’s portfolio maturity and average effective duration may be reduced for defensive purposes. There is no limitation on the maturity of any specific security the Fund may purchase. The Fund may dispose of any security before it matures. The Fund also attempts to reduce changes in its share value through credit analysis, selection and diversification.

The Fund ordinarily acquires and holds securities for investment rather than for realization of gains by short-term trading on market fluctuations. However, it may sell an investment prior to its scheduled maturity date to enhance income or reduce loss, to change the portfolio’s average duration or average maturity, to pursue other investment opportunities, in response to changes in the conditions or business of the investment’s issuer or changes in overall market conditions, or if, in Thornburg’s opinion, the investment no longer serves to achieve the Fund’s investment goals.  The objective of preserving capital may prevent the Fund from obtaining the highest yields available.

Under normal conditions the Fund invests at least 80% of its assets in municipal obligations originating in New York State which are exempt from New York State and regular federal income taxes, and normally invests 100% of its assets in municipal obligations originating in New York or issued by United States territories and possessions and exempt from regular federal income tax. The Fund may invest up to 20% of its assets in taxable securities which would produce income not exempt from

federal or New York income tax because of market conditions, pending investment of idle funds or to afford liquidity. The Fund’s temporary taxable investments may exceed 20% of its assets when made for defensive purposes during periods of abnormal market conditions. If the Fund found it necessary to own taxable investments, some of the Fund’s income would be subject to federal and New York State and City income taxes.
Risk [Heading] rr_RiskHeading Principal Investment Risks
Risk Narrative [Text Block] rr_RiskNarrativeTextBlock

An investment in the Fund is not a deposit in any bank and is not insured or guaranteed by the Federal Deposit Insurance Corporation or any other government agency. Accordingly, the loss of money is a risk of investing in the Fund. The value of the Fund’s shares and its dividends may fluctuate from day to day and over time, and when you sell your shares they may be worth less than what you paid for them. The following is a summary of the principal risks of investing in the Fund.

Management Risk – The Fund is an actively managed portfolio, and the value of the Fund may be reduced if Thornburg pursues unsuccessful investments or fails to correctly identify risks affecting the broad economy or specific issuers in which the Fund invests.

Interest Rate Risk – When interest rates increase, the value of the Fund’s investments may decline and the Fund’s share value may be reduced. This effect is typically more pronounced for intermediate and longer-term obligations. When interest rates decrease, the Fund’s dividends may decline. Decreases in market interest rates may also result in prepayments of obligations the Fund acquires, requiring the Fund to reinvest at lower interest rates.

Credit Risk – If obligations held by the Fund are downgraded by ratings agencies or go into default, or if legislation or other government action reduces the ability of issuers to pay principal and interest when due, the value of those obligations may decline and the Fund’s share value and the dividends paid by the Fund may be reduced. Lower-rated or unrated obligations held by the Fund may have, or may be perceived to have, greater risk of default and ratings downgrades. For example, municipal leases held by the Fund may be subject to non-appropriation provisions which permit governmental agencies or issuers to discontinue payments to the Fund under the municipal leases.

Market and Economic Risk – The value of the Fund’s investments may decline and its share value may be reduced due to changes in general economic and market conditions. This effect is typically more pronounced for the Fund’s investments in lower-rated and unrated municipal obligations, the value of which may fluctuate more significantly in response to poor economic growth or other changes in market conditions, political, economic and legal developments, and developments affecting specific issuers.

Liquidity Risk – Due to a lack of demand in the marketplace or other factors, the Fund may not be able to sell promptly some or all of the obligations that it holds, or may only be able to sell obligations at less than desired prices. The market for lower-rated and unrated obligations may be less liquid than the market for other obligations, making it difficult for the Fund to value its investment in a lower-rated or unrated obligation or to sell the investment in a timely manner or at an acceptable price.

Single State Risk – Because the Fund invests primarily in obligations originating in New York, the Fund’s share value may be more sensitive to adverse economic, political or regulatory developments in that state. Budgetary concerns, decreased revenues, and adverse conditions significant to a sector of the state, municipalities within the state, or local economies may negatively affect the ability of state and local issuers to make full and timely principal or interest payments on their debt obligations.

Non-diversification Risk – The Fund is a non-diversified investment company, which means that it may invest a greater proportion of its assets in the securities of a single issuer. This may be riskier, because a default or other adverse condition affecting such an issuer could cause the Fund’s share price to decline to a greater degree.

Cybersecurity and Operational Risk – Operational failures, cyber-attacks or other disruptions that affect the Fund’s service providers, the Fund’s counterparties, other market participants or the issuers of securities held by the Fund may adversely affect the Fund and its shareholders, including by causing losses for the Fund or impairing Fund operations.

Additional information about Fund investments, investment strategies and risks of investing in the Fund appears beginning on page 118 of the Prospectus.
Risk Lose Money [Text] rr_RiskLoseMoney Accordingly, the loss of money is a risk of investing in the Fund.
RIsk Not Insured [Text] rr_RiskNotInsured An investment in the Fund is not a deposit in any bank and is not insured or guaranteed by the Federal Deposit Insurance Corporation or any other government agency.
Risk Nondiversified Status [Text] rr_RiskNondiversifiedStatus The Fund is a non-diversified investment company, which means that it may invest a greater proportion of its assets in the securities of a single issuer.
Bar Chart and Performance Table [Heading] rr_BarChartAndPerformanceTableHeading Past Performance of the Fund
Performance Narrative [Text Block] rr_PerformanceNarrativeTextBlock

The following information provides some indication of the risks of investing in Intermediate New York Fund by showing how the Fund’s investment results vary from year to year. The bar chart shows how the annual total returns for Class A shares have been different in each full year shown. The average annual total return figures compare Class A and Class I share performance

to the ICE BofAML 3-15 Year U.S. Municipal Securities Index, a broad measure of market performance. Past performance (before and after taxes) is not necessarily an indication of how the Fund will perform in the future. The performance information shown is as of the calendar year ended December 31, 2021. Updated performance information may be obtained on the Thornburg website at Thornburg.com or by calling 1-800-847-0200.
Performance Information Illustrates Variability of Returns [Text] rr_PerformanceInformationIllustratesVariabilityOfReturns The following information provides some indication of the risks of investing in Intermediate New York Fund by showing how the Fund’s investment results vary from year to year.
Performance Availability Phone [Text] rr_PerformanceAvailabilityPhone 1-800-847-0200
Performance Past Does Not Indicate Future [Text] rr_PerformancePastDoesNotIndicateFuture Past performance (before and after taxes) is not necessarily an indication of how the Fund will perform in the future.
Bar Chart [Heading] rr_BarChartHeading Annual Total Returns – Class A Shares
Bar Chart Does Not Reflect Sales Loads [Text] rr_BarChartDoesNotReflectSalesLoads The sales charge for Class A shares is not reflected in the returns shown in the bar chart, and the returns would be less if the charge was taken into account.
Bar Chart Closing [Text Block] rr_BarChartClosingTextBlock

Total
Returns

Quarter
ended

Highest Quarterly Results

3.86%

6/30/2011

Lowest Quarterly Results

(3.09)%

12/31/2016

The sales charge for Class A shares is not reflected in the returns shown in the bar chart, and the returns would be less if the charge was taken into account.
Performance Table Heading rr_PerformanceTableHeading Average Annual Total Returns (periods ended 12-31-21)
Performance Table Uses Highest Federal Rate rr_PerformanceTableUsesHighestFederalRate After-tax returns are calculated using the highest historical individual federal marginal income tax rates, and do not reflect state or local income taxes.
Performance Table Not Relevant to Tax Deferred rr_PerformanceTableNotRelevantToTaxDeferred Actual after-tax returns depend on an investor’s own tax situation and may differ from the returns shown, and after-tax returns shown are not relevant to investors who hold their Fund shares through tax-deferred arrangements, such as 401(k) plans or individual retirement accounts.
Performance Table One Class of after Tax Shown [Text] rr_PerformanceTableOneClassOfAfterTaxShown The after-tax returns shown relate only to Class A shares, and after-tax returns for other share classes will vary.
Performance Table Closing [Text Block] rr_PerformanceTableClosingTextBlock

After-tax returns are calculated using the highest historical individual federal marginal income tax rates, and do not reflect state or local income taxes. Actual after-tax returns depend on an investor’s own tax situation and may differ from the returns shown, and after-tax returns shown are not relevant to investors who hold their Fund shares through tax-deferred arrangements, such as 401(k) plans or individual retirement accounts. The after-tax returns shown relate only to Class A shares, and after-tax returns for other share classes will vary.

Retail | Thornburg New York Intermediate Municipal Fund | Thornburg New York Intermediate Municipal Fund - Class A  
Prospectus [Line Items] rr_ProspectusLineItems  
Trading Symbol dei_TradingSymbol THNYX
Maximum Sales Charge Imposed on Purchases (as a percentage of Offering Price) rr_MaximumSalesChargeImposedOnPurchasesOverOfferingPrice 2.00%
Maximum Deferred Sales Charge (as a percentage) rr_MaximumDeferredSalesChargeOverOther none [52]
Management Fees (as a percentage of Assets) rr_ManagementFeesOverAssets 0.50%
Distribution and Service (12b-1) Fees rr_DistributionAndService12b1FeesOverAssets 0.25%
Other Expenses (as a percentage of Assets): rr_OtherExpensesOverAssets 0.39%
Expenses (as a percentage of Assets) rr_ExpensesOverAssets 1.14%
Fee Waiver or Reimbursement rr_FeeWaiverOrReimbursementOverAssets (0.15%) [53]
Net Expenses (as a percentage of Assets) rr_NetExpensesOverAssets 0.99%
Expense Example, with Redemption, 1 Year rr_ExpenseExampleYear01 $ 299
Expense Example, with Redemption, 3 Years rr_ExpenseExampleYear03 540
Expense Example, with Redemption, 5 Years rr_ExpenseExampleYear05 801
Expense Example, with Redemption, 10 Years rr_ExpenseExampleYear10 $ 1,545
Annual Return 2012 rr_AnnualReturn2012 4.92%
Annual Return 2013 rr_AnnualReturn2013 (1.90%)
Annual Return 2014 rr_AnnualReturn2014 5.81%
Annual Return 2015 rr_AnnualReturn2015 2.18%
Annual Return 2016 rr_AnnualReturn2016 (0.51%)
Annual Return 2017 rr_AnnualReturn2017 2.67%
Annual Return 2018 rr_AnnualReturn2018 0.16%
Annual Return 2019 rr_AnnualReturn2019 4.56%
Annual Return 2020 rr_AnnualReturn2020 2.99%
Annual Return 2021 rr_AnnualReturn2021 0.32%
Highest Quarterly Return, Label rr_HighestQuarterlyReturnLabel Highest Quarterly Results
Highest Quarterly Return, Date rr_BarChartHighestQuarterlyReturnDate Jun. 30, 2011
Highest Quarterly Return rr_BarChartHighestQuarterlyReturn 3.86%
Lowest Quarterly Return, Label rr_LowestQuarterlyReturnLabel Lowest Quarterly Results
Lowest Quarterly Return, Date rr_BarChartLowestQuarterlyReturnDate Dec. 31, 2016
Lowest Quarterly Return rr_BarChartLowestQuarterlyReturn (3.09%)
1 Year rr_AverageAnnualReturnYear01 (1.71%)
5 Years rr_AverageAnnualReturnYear05 1.72%
10 Years rr_AverageAnnualReturnYear10 1.88%
Retail | Thornburg New York Intermediate Municipal Fund | Thornburg New York Intermediate Municipal Fund - Class A | After Taxes on Distributions  
Prospectus [Line Items] rr_ProspectusLineItems  
1 Year rr_AverageAnnualReturnYear01 (1.72%)
5 Years rr_AverageAnnualReturnYear05 1.72%
10 Years rr_AverageAnnualReturnYear10 1.88%
Retail | Thornburg New York Intermediate Municipal Fund | Thornburg New York Intermediate Municipal Fund - Class A | After Taxes on Distributions and Sales  
Prospectus [Line Items] rr_ProspectusLineItems  
1 Year rr_AverageAnnualReturnYear01 (0.30%)
5 Years rr_AverageAnnualReturnYear05 1.83%
10 Years rr_AverageAnnualReturnYear10 1.97%
Retail | Thornburg New York Intermediate Municipal Fund | Thornburg New York Intermediate Municipal Fund - Class A | ICE BofAML 3-15 Year U.S. Municipal Securities Index (reflects no deduction for fees, expenses, or taxes)  
Prospectus [Line Items] rr_ProspectusLineItems  
1 Year rr_AverageAnnualReturnYear01 0.94%
5 Years rr_AverageAnnualReturnYear05 3.77%
10 Years rr_AverageAnnualReturnYear10 3.22%
Retail | Thornburg New York Intermediate Municipal Fund | Thornburg New York Intermediate Municipal Fund - Class I  
Prospectus [Line Items] rr_ProspectusLineItems  
Trading Symbol dei_TradingSymbol TNYIX
Maximum Sales Charge Imposed on Purchases (as a percentage of Offering Price) rr_MaximumSalesChargeImposedOnPurchasesOverOfferingPrice none
Maximum Deferred Sales Charge (as a percentage) rr_MaximumDeferredSalesChargeOverOther none
Management Fees (as a percentage of Assets) rr_ManagementFeesOverAssets 0.50%
Distribution and Service (12b-1) Fees rr_DistributionAndService12b1FeesOverAssets none
Other Expenses (as a percentage of Assets): rr_OtherExpensesOverAssets 0.43%
Expenses (as a percentage of Assets) rr_ExpensesOverAssets 0.93%
Fee Waiver or Reimbursement rr_FeeWaiverOrReimbursementOverAssets (0.26%) [53]
Net Expenses (as a percentage of Assets) rr_NetExpensesOverAssets 0.67%
Expense Example, with Redemption, 1 Year rr_ExpenseExampleYear01 $ 68
Expense Example, with Redemption, 3 Years rr_ExpenseExampleYear03 270
Expense Example, with Redemption, 5 Years rr_ExpenseExampleYear05 489
Expense Example, with Redemption, 10 Years rr_ExpenseExampleYear10 $ 1,119
1 Year rr_AverageAnnualReturnYear01 0.64%
5 Years rr_AverageAnnualReturnYear05 2.45%
10 Years rr_AverageAnnualReturnYear10 2.42%
Retail | Thornburg New York Intermediate Municipal Fund | Thornburg New York Intermediate Municipal Fund - Class I | ICE BofAML 3-15 Year U.S. Municipal Securities Index (reflects no deduction for fees, expenses, or taxes)  
Prospectus [Line Items] rr_ProspectusLineItems  
1 Year rr_AverageAnnualReturnYear01 0.94%
5 Years rr_AverageAnnualReturnYear05 3.77%
10 Years rr_AverageAnnualReturnYear10 3.22%
Retail | Thornburg Intermediate Municipal Fund  
Prospectus [Line Items] rr_ProspectusLineItems  
Risk/Return [Heading] rr_RiskReturnHeading Intermediate Municipal Fund
Objective [Heading] rr_ObjectiveHeading Investment Goal
Objective, Primary [Text Block] rr_ObjectivePrimaryTextBlock

The primary investment goal of Intermediate Municipal Fund is to obtain as high a level of current income exempt from federal individual income tax as is consistent, in the view of the Fund’s investment advisor, with preservation of capital.
Objective, Secondary [Text Block] rr_ObjectiveSecondaryTextBlock

The secondary goal of the Fund is to reduce expected changes in its share price compared to long-term bond portfolios.
Expense [Heading] rr_ExpenseHeading Fees and Expenses of the Fund
Expense Narrative [Text Block] rr_ExpenseNarrativeTextBlock

This table describes the fees and expenses that you may pay if you buy and hold shares of the Fund. You may qualify for discounts from the sales charges applicable to Class A shares if you or other qualifying account holders invest, or agree to invest in the future, at least $50,000 in the Thornburg Funds. More information about this and other discounts and sales charge waivers is available from your financial intermediary, in the Prospectus under the captions “Class A Sales Charge Waivers,” beginning on page 146, and “Appendix A – Sales Charge Waivers Offered by Financial Intermediaries,” beginning on page 200, and in the Statement of Additional Information under the caption “Additional Information Respecting Purchase and Redemption of Shares,” beginning on page 108.
Shareholder Fees Caption [Text] rr_ShareholderFeesCaption Shareholder Fees (fees paid directly from your investment)
Operating Expenses Caption [Text] rr_OperatingExpensesCaption Annual Fund Operating Expenses (expenses that you pay each year as a percentage of the value of your investment)
Fee Waiver or Reimbursement over Assets, Date of Termination rr_FeeWaiverOrReimbursementOverAssetsDateOfTermination February 1, 2023
Portfolio Turnover [Heading] rr_PortfolioTurnoverHeading Portfolio Turnover.
Portfolio Turnover [Text Block] rr_PortfolioTurnoverTextBlock

The Fund pays transaction costs, such as commissions, when it buys and sells securities (or “turns over”) its portfolio. A higher portfolio turnover rate may indicate higher transaction costs and may result in higher taxes when Fund shares are held in a taxable account. These costs, which are not reflected in Annual Fund Operating Expenses or in the Example, affect the Fund’s performance. During the most recent fiscal year, the Fund’s portfolio turnover rate was 10.20% of the average value of its portfolio.
Portfolio Turnover, Rate rr_PortfolioTurnoverRate 10.20%
Expense Breakpoint Discounts [Text] rr_ExpenseBreakpointDiscounts You may qualify for discounts from the sales charges applicable to Class A shares if you or other qualifying account holders invest, or agree to invest in the future, at least $50,000 in the Thornburg Funds.
Expense Breakpoint, Minimum Investment Required [Amount] rr_ExpenseBreakpointMinimumInvestmentRequiredAmount $ 50,000
Expense Example [Heading] rr_ExpenseExampleHeading Example.
Expense Example Narrative [Text Block] rr_ExpenseExampleNarrativeTextBlock

This Example is intended to help you compare the cost of investing in the Fund with the cost of investing in other mutual funds.

The Example assumes that you invest $10,000 in the Fund for the time periods indicated and then redeem all of your shares at the end of those periods. The Example also assumes that your investment has a 5% return each year, dividends and distributions are reinvested, and that the Fund’s operating expenses remain the same. Although your actual costs may be higher or lower, based on these assumptions, your costs would be:
Expense Example, No Redemption Narrative [Text Block] rr_ExpenseExampleNoRedemptionNarrativeTextBlock

You would pay the following expenses if you did not redeem your Class C shares:
Strategy [Heading] rr_StrategyHeading Principal Investment Strategies
Strategy Narrative [Text Block] rr_StrategyNarrativeTextBlock

The Fund pursues its primary goal by investing principally in a laddered maturity portfolio of municipal obligations issued by states and state agencies, local governments and their agencies, and by United States territories and possessions. Thornburg Investment Management, Inc. (“Thornburg”) actively manages the Fund’s portfolio. Investment decisions are based upon outlooks for interest rates and securities markets, the supply of municipal debt obligations, and analysis of specific securities. The Fund invests in obligations and participations in obligations which are rated by a nationally recognized statistical rating organization at the time of purchase as investment grade or, if unrated, are issued by obligors which Thornburg determines have comparable investment grade obligations outstanding or which are deemed by Thornburg to be comparable to obligors with outstanding investment grade obligations. “Participations” are undivided interests in pools of securities where the underlying credit support passes through to the participants. The Fund’s portfolio is “laddered” by investing in obligations of different maturities so that some obligations mature during each of the coming years.

Because the magnitude of changes in value of interest-bearing obligations is greater for obligations with longer terms given an equivalent change in interest rates, the Fund seeks to reduce changes in its share value by maintaining a portfolio of investments with a dollar-weighted average maturity of normally three to ten years. As a result, the Fund also maintains a portfolio of investments having a dollar-weighted average effective duration of normally no more than ten years. Duration is a measure of estimated sensitivity to interest rate changes. A portfolio with a longer average effective duration will typically be more sensitive to interest rate changes than a portfolio with a shorter average effective duration. Duration is commonly expressed as a number, which is the expected percentage change in an obligation’s price upon a 1% change in interest rates. For example, an obligation with a duration of 10 would be expected to change in price by approximately 10% in response to a 1% change in interest rates. During temporary periods the Fund’s portfolio maturity and average effective duration may be reduced for defensive purposes. There is no limitation on the maturity of any specific security the Fund may purchase. The Fund may dispose of any security before it matures. The Fund also attempts to reduce changes in its share value through credit analysis, selection and diversification.

The Fund ordinarily acquires and holds securities for investment rather than for realization of gains by short-term trading on market fluctuations. However, it may sell an investment prior to its scheduled maturity date to enhance income or reduce loss, to change the portfolio’s average duration or average maturity, to pursue other investment opportunities, in response to

changes in the conditions or business of the investment’s issuer or changes in overall market conditions, or if, in Thornburg’s opinion, the investment no longer serves to achieve the Fund’s investment goals.  The objective of preserving capital may prevent the Fund from obtaining the highest yields available.

The Fund normally invests 100% of its assets in municipal obligations, the income from which is exempt from the regular federal income tax. The Fund may invest up to 20% of its assets in taxable securities which would produce income not exempt from federal income tax because of market conditions, pending investment of idle funds or to afford liquidity. The Fund’s temporary taxable investments may exceed 20% of its assets when made for defensive purposes during periods of abnormal market conditions. If the Fund found it necessary to own taxable investments, some of its income would be subject to federal income tax.
Risk [Heading] rr_RiskHeading Principal Investment Risks
Risk Narrative [Text Block] rr_RiskNarrativeTextBlock

An investment in the Fund is not a deposit in any bank and is not insured or guaranteed by the Federal Deposit Insurance Corporation or any other government agency. Accordingly, the loss of money is a risk of investing in the Fund. The value of the Fund’s shares and its dividends may fluctuate from day to day and over time, and when you sell your shares they may be worth less than what you paid for them. The following is a summary of the principal risks of investing in the Fund.

Management Risk – The Fund is an actively managed portfolio, and the value of the Fund may be reduced if Thornburg pursues unsuccessful investments or fails to correctly identify risks affecting the broad economy or specific issuers in which the Fund invests.

Interest Rate Risk – When interest rates increase, the value of the Fund’s investments may decline and the Fund’s share value may be reduced. This effect is typically more pronounced for intermediate and longer-term obligations. When interest rates decrease, the Fund’s dividends may decline. Decreases in market interest rates may also result in prepayments of obligations the Fund acquires, requiring the Fund to reinvest at lower interest rates.

Credit Risk – If obligations held by the Fund are downgraded by ratings agencies or go into default, or if legislation or other government action reduces the ability of issuers to pay principal and interest when due, the value of those obligations may decline and the Fund’s share value and the dividends paid by the Fund may be reduced. Lower-rated or unrated obligations held by the Fund may have, or may be perceived to have, greater risk of default and ratings downgrades. For example, municipal leases held by the Fund may be subject to non-appropriation provisions which permit governmental agencies or issuers to discontinue payments to the Fund under the municipal leases.

Market and Economic Risk – The value of the Fund’s investments may decline and its share value may be reduced due to changes in general economic and market conditions. This effect is typically more pronounced for the Fund’s investments in lower-rated and unrated municipal obligations, the value of which may fluctuate more significantly in response to poor economic growth or other changes in market conditions, political, economic and legal developments, and developments affecting specific issuers.

Liquidity Risk – Due to a lack of demand in the marketplace or other factors, the Fund may not be able to sell promptly some or all of the obligations that it holds, or may only be able to sell obligations at less than desired prices. The market for lower-rated and unrated obligations may be less liquid than the market for other obligations, making it difficult for the Fund to value its investment in a lower-rated or unrated obligation or to sell the investment in a timely manner or at an acceptable price.

Cybersecurity and Operational Risk – Operational failures, cyber-attacks or other disruptions that affect the Fund’s service providers, the Fund’s counterparties, other market participants or the issuers of securities held by the Fund may adversely affect the Fund and its shareholders, including by causing losses for the Fund or impairing Fund operations.

Additional information about Fund investments, investment strategies and risks of investing in the Fund appears beginning on page 118 of the Prospectus.
Risk Lose Money [Text] rr_RiskLoseMoney Accordingly, the loss of money is a risk of investing in the Fund.
RIsk Not Insured [Text] rr_RiskNotInsured An investment in the Fund is not a deposit in any bank and is not insured or guaranteed by the Federal Deposit Insurance Corporation or any other government agency.
Bar Chart and Performance Table [Heading] rr_BarChartAndPerformanceTableHeading Past Performance of the Fund
Performance Narrative [Text Block] rr_PerformanceNarrativeTextBlock

The following information provides some indication of the risks of investing in Intermediate Municipal Fund by showing how the Fund’s investment results vary from year to year. The bar chart shows how the annual total returns for Class A shares have been different in each full year shown. The average annual total return figures compare Class A, Class C, Class C2 and Class I share performance to the ICE BofAML 3-15 Year U.S. Municipal Securities Index, a broad measure of market performance. Past performance (before and after taxes) is not necessarily an indication of how the Fund will perform in the future. The performance information shown is as of the calendar year ended December 31, 2021. Updated performance information may be obtained on the Thornburg website at Thornburg.com or by calling 1-800-847-0200.
Performance Information Illustrates Variability of Returns [Text] rr_PerformanceInformationIllustratesVariabilityOfReturns The following information provides some indication of the risks of investing in Intermediate Municipal Fund by showing how the Fund’s investment results vary from year to year.
Performance Availability Phone [Text] rr_PerformanceAvailabilityPhone 1-800-847-0200
Performance Availability Website Address [Text] rr_PerformanceAvailabilityWebSiteAddress Thornburg.com
Performance Past Does Not Indicate Future [Text] rr_PerformancePastDoesNotIndicateFuture Past performance (before and after taxes) is not necessarily an indication of how the Fund will perform in the future.
Bar Chart [Heading] rr_BarChartHeading Annual Total Returns – Class A Shares
Bar Chart Does Not Reflect Sales Loads [Text] rr_BarChartDoesNotReflectSalesLoads The sales charge for Class A shares is not reflected in the returns shown in the bar chart above, and the returns would be less if the charge was taken into account.
Bar Chart Closing [Text Block] rr_BarChartClosingTextBlock

Total
Returns

Quarter
ended

Highest Quarterly Results

3.41%

6/30/2011

Lowest Quarterly Results

(3.23)%

12/31/2016

The sales charge for Class A shares is not reflected in the returns shown in the bar chart above, and the returns would be less if the charge was taken into account.
Performance Table Heading rr_PerformanceTableHeading Average Annual Total Returns (periods ended 12-31-21)
Performance Table Uses Highest Federal Rate rr_PerformanceTableUsesHighestFederalRate fter-tax returns are calculated using the historical highest individual federal marginal income tax rates, and do not reflect state or local income taxes.
Performance Table Not Relevant to Tax Deferred rr_PerformanceTableNotRelevantToTaxDeferred Actual after-tax returns depend on an investor’s own tax situation and may differ from the returns shown, and after-tax returns shown are not relevant to investors who hold their Fund shares through tax-deferred arrangements, such as 401(k) plans or individual retirement accounts.
Performance Table One Class of after Tax Shown [Text] rr_PerformanceTableOneClassOfAfterTaxShown The after-tax returns shown relate only to Class A shares, and after-tax returns for other share classes will vary.
Performance Table Closing [Text Block] rr_PerformanceTableClosingTextBlock

After-tax returns are calculated using the historical highest individual federal marginal income tax rates, and do not reflect state or local income taxes. Actual after-tax returns depend on an investor’s own tax situation and may differ from the returns shown, and after-tax returns shown are not relevant to investors who hold their Fund shares through tax-deferred arrangements, such as 401(k) plans or individual retirement accounts. The after-tax returns shown relate only to Class A shares, and after-tax returns for other share classes will vary.
Retail | Thornburg Intermediate Municipal Fund | Thornburg Intermediate Municipal Fund - Class A  
Prospectus [Line Items] rr_ProspectusLineItems  
Trading Symbol dei_TradingSymbol THIMX
Maximum Sales Charge Imposed on Purchases (as a percentage of Offering Price) rr_MaximumSalesChargeImposedOnPurchasesOverOfferingPrice 2.00%
Maximum Deferred Sales Charge (as a percentage) rr_MaximumDeferredSalesChargeOverOther none [54]
Management Fees (as a percentage of Assets) rr_ManagementFeesOverAssets 0.47%
Distribution and Service (12b-1) Fees rr_DistributionAndService12b1FeesOverAssets 0.25%
Other Expenses (as a percentage of Assets): rr_OtherExpensesOverAssets 0.19%
Expenses (as a percentage of Assets) rr_ExpensesOverAssets 0.91% [55]
Fee Waiver or Reimbursement rr_FeeWaiverOrReimbursementOverAssets (0.14%)
Net Expenses (as a percentage of Assets) rr_NetExpensesOverAssets 0.77%
Expense Example, with Redemption, 1 Year rr_ExpenseExampleYear01 $ 277
Expense Example, with Redemption, 3 Years rr_ExpenseExampleYear03 471
Expense Example, with Redemption, 5 Years rr_ExpenseExampleYear05 680
Expense Example, with Redemption, 10 Years rr_ExpenseExampleYear10 $ 1,285
Annual Return 2012 rr_AnnualReturn2012 5.99%
Annual Return 2013 rr_AnnualReturn2013 (1.28%)
Annual Return 2014 rr_AnnualReturn2014 6.55%
Annual Return 2015 rr_AnnualReturn2015 2.11%
Annual Return 2016 rr_AnnualReturn2016 (0.50%)
Annual Return 2017 rr_AnnualReturn2017 3.61%
Annual Return 2018 rr_AnnualReturn2018 0.56%
Annual Return 2019 rr_AnnualReturn2019 5.64%
Annual Return 2020 rr_AnnualReturn2020 3.81%
Annual Return 2021 rr_AnnualReturn2021 0.99%
Highest Quarterly Return, Label rr_HighestQuarterlyReturnLabel Highest Quarterly Results
Highest Quarterly Return, Date rr_BarChartHighestQuarterlyReturnDate Jun. 30, 2011
Highest Quarterly Return rr_BarChartHighestQuarterlyReturn 3.41%
Lowest Quarterly Return, Label rr_LowestQuarterlyReturnLabel Lowest Quarterly Results
Lowest Quarterly Return, Date rr_BarChartLowestQuarterlyReturnDate Dec. 31, 2016
Lowest Quarterly Return rr_BarChartLowestQuarterlyReturn (3.23%)
1 Year rr_AverageAnnualReturnYear01 (1.06%)
5 Years rr_AverageAnnualReturnYear05 2.49%
10 Years rr_AverageAnnualReturnYear10 2.51%
Retail | Thornburg Intermediate Municipal Fund | Thornburg Intermediate Municipal Fund - Class A | After Taxes on Distributions  
Prospectus [Line Items] rr_ProspectusLineItems  
1 Year rr_AverageAnnualReturnYear01 (1.06%)
5 Years rr_AverageAnnualReturnYear05 2.49%
10 Years rr_AverageAnnualReturnYear10 2.51%
Retail | Thornburg Intermediate Municipal Fund | Thornburg Intermediate Municipal Fund - Class A | After Taxes on Distributions and Sales  
Prospectus [Line Items] rr_ProspectusLineItems  
1 Year rr_AverageAnnualReturnYear01 0.27%
5 Years rr_AverageAnnualReturnYear05 2.46%
10 Years rr_AverageAnnualReturnYear10 2.47%
Retail | Thornburg Intermediate Municipal Fund | Thornburg Intermediate Municipal Fund - Class A | ICE BofAML 3-15 Year U.S. Municipal Securities Index (reflects no deduction for fees, expenses, or taxes)  
Prospectus [Line Items] rr_ProspectusLineItems  
1 Year rr_AverageAnnualReturnYear01 0.94%
5 Years rr_AverageAnnualReturnYear05 3.77%
10 Years rr_AverageAnnualReturnYear10 3.22%
Retail | Thornburg Intermediate Municipal Fund | Thornburg Intermediate Municipal Fund - Class C  
Prospectus [Line Items] rr_ProspectusLineItems  
Trading Symbol dei_TradingSymbol THMCX
Maximum Sales Charge Imposed on Purchases (as a percentage of Offering Price) rr_MaximumSalesChargeImposedOnPurchasesOverOfferingPrice none
Maximum Deferred Sales Charge (as a percentage) rr_MaximumDeferredSalesChargeOverOther 0.60% [56]
Management Fees (as a percentage of Assets) rr_ManagementFeesOverAssets 0.47%
Distribution and Service (12b-1) Fees rr_DistributionAndService12b1FeesOverAssets 0.60%
Other Expenses (as a percentage of Assets): rr_OtherExpensesOverAssets 0.23%
Expenses (as a percentage of Assets) rr_ExpensesOverAssets 1.30% [55]
Fee Waiver or Reimbursement rr_FeeWaiverOrReimbursementOverAssets (0.16%)
Net Expenses (as a percentage of Assets) rr_NetExpensesOverAssets 1.14%
Expense Example, with Redemption, 1 Year rr_ExpenseExampleYear01 $ 176
Expense Example, with Redemption, 3 Years rr_ExpenseExampleYear03 396
Expense Example, with Redemption, 5 Years rr_ExpenseExampleYear05 698
Expense Example, with Redemption, 10 Years rr_ExpenseExampleYear10 1,554
Expense Example, No Redemption, 1 Year rr_ExpenseExampleNoRedemptionYear01 116
Expense Example, No Redemption, 3 Years rr_ExpenseExampleNoRedemptionYear03 396
Expense Example, No Redemption, 5 Years rr_ExpenseExampleNoRedemptionYear05 698
Expense Example, No Redemption, 10 Years rr_ExpenseExampleNoRedemptionYear10 $ 1,554
1 Year rr_AverageAnnualReturnYear01 0.02%
5 Years rr_AverageAnnualReturnYear05 2.54%
10 Years rr_AverageAnnualReturnYear10 2.37%
Retail | Thornburg Intermediate Municipal Fund | Thornburg Intermediate Municipal Fund - Class C | ICE BofAML 3-15 Year U.S. Municipal Securities Index (reflects no deduction for fees, expenses, or taxes)  
Prospectus [Line Items] rr_ProspectusLineItems  
1 Year rr_AverageAnnualReturnYear01 0.94%
5 Years rr_AverageAnnualReturnYear05 3.77%
10 Years rr_AverageAnnualReturnYear10 3.22%
Retail | Thornburg Intermediate Municipal Fund | Thornburg Intermediate Municipal Fund - Class C2  
Prospectus [Line Items] rr_ProspectusLineItems  
Trading Symbol dei_TradingSymbol THMQX
Maximum Sales Charge Imposed on Purchases (as a percentage of Offering Price) rr_MaximumSalesChargeImposedOnPurchasesOverOfferingPrice none
Maximum Deferred Sales Charge (as a percentage) rr_MaximumDeferredSalesChargeOverOther 0.65% [56]
Management Fees (as a percentage of Assets) rr_ManagementFeesOverAssets 0.47%
Distribution and Service (12b-1) Fees rr_DistributionAndService12b1FeesOverAssets 0.65%
Other Expenses (as a percentage of Assets): rr_OtherExpensesOverAssets 1.50%
Expenses (as a percentage of Assets) rr_ExpensesOverAssets 2.62% [55]
Fee Waiver or Reimbursement rr_FeeWaiverOrReimbursementOverAssets (1.48%)
Net Expenses (as a percentage of Assets) rr_NetExpensesOverAssets 1.14%
Expense Example, with Redemption, 1 Year rr_ExpenseExampleYear01 $ 181
Expense Example, with Redemption, 3 Years rr_ExpenseExampleYear03 673
Expense Example, with Redemption, 5 Years rr_ExpenseExampleYear05 1,258
Expense Example, with Redemption, 10 Years rr_ExpenseExampleYear10 2,844
Expense Example, No Redemption, 1 Year rr_ExpenseExampleNoRedemptionYear01 116
Expense Example, No Redemption, 3 Years rr_ExpenseExampleNoRedemptionYear03 673
Expense Example, No Redemption, 5 Years rr_ExpenseExampleNoRedemptionYear05 1,258
Expense Example, No Redemption, 10 Years rr_ExpenseExampleNoRedemptionYear10 $ 2,844
1 Year rr_AverageAnnualReturnYear01 (0.03%)
Since Inception rr_AverageAnnualReturnSinceInception 1.53%
Inception Date rr_AverageAnnualReturnInceptionDate Oct. 01, 2020
Retail | Thornburg Intermediate Municipal Fund | Thornburg Intermediate Municipal Fund - Class C2 | ICE BofAML 3-15 Year U.S. Municipal Securities Index (reflects no deduction for fees, expenses, or taxes)  
Prospectus [Line Items] rr_ProspectusLineItems  
1 Year rr_AverageAnnualReturnYear01 0.94%
Since Inception rr_AverageAnnualReturnSinceInception 2.01%
Retail | Thornburg Intermediate Municipal Fund | Thornburg Intermediate Municipal Fund - Class I  
Prospectus [Line Items] rr_ProspectusLineItems  
Trading Symbol dei_TradingSymbol THMIX
Maximum Sales Charge Imposed on Purchases (as a percentage of Offering Price) rr_MaximumSalesChargeImposedOnPurchasesOverOfferingPrice none
Maximum Deferred Sales Charge (as a percentage) rr_MaximumDeferredSalesChargeOverOther none
Management Fees (as a percentage of Assets) rr_ManagementFeesOverAssets 0.47%
Distribution and Service (12b-1) Fees rr_DistributionAndService12b1FeesOverAssets none
Other Expenses (as a percentage of Assets): rr_OtherExpensesOverAssets 0.20%
Expenses (as a percentage of Assets) rr_ExpensesOverAssets 0.67% [55]
Fee Waiver or Reimbursement rr_FeeWaiverOrReimbursementOverAssets (0.14%)
Net Expenses (as a percentage of Assets) rr_NetExpensesOverAssets 0.53%
Expense Example, with Redemption, 1 Year rr_ExpenseExampleYear01 $ 54
Expense Example, with Redemption, 3 Years rr_ExpenseExampleYear03 200
Expense Example, with Redemption, 5 Years rr_ExpenseExampleYear05 359
Expense Example, with Redemption, 10 Years rr_ExpenseExampleYear10 $ 821
1 Year rr_AverageAnnualReturnYear01 1.23%
5 Years rr_AverageAnnualReturnYear05 3.15%
10 Years rr_AverageAnnualReturnYear10 3.00%
Retail | Thornburg Intermediate Municipal Fund | Thornburg Intermediate Municipal Fund - Class I | ICE BofAML 3-15 Year U.S. Municipal Securities Index (reflects no deduction for fees, expenses, or taxes)  
Prospectus [Line Items] rr_ProspectusLineItems  
1 Year rr_AverageAnnualReturnYear01 0.94%
5 Years rr_AverageAnnualReturnYear05 3.77%
10 Years rr_AverageAnnualReturnYear10 3.22%
Retail | Thornburg Strategic Municipal Income Fund  
Prospectus [Line Items] rr_ProspectusLineItems  
Risk/Return [Heading] rr_RiskReturnHeading Strategic Municipal Income Fund
Objective [Heading] rr_ObjectiveHeading Investment Goal
Objective, Primary [Text Block] rr_ObjectivePrimaryTextBlock

The Fund seeks a high level of current income exempt from federal individual income tax.
Expense [Heading] rr_ExpenseHeading Fees and Expenses of the Fund
Expense Narrative [Text Block] rr_ExpenseNarrativeTextBlock

This table describes the fees and expenses that you may pay if you buy and hold shares of the Fund. You may qualify for discounts from the sales charges applicable to Class A shares if you or other qualifying account holders invest, or agree to invest in the future, at least $50,000 in the Thornburg Funds. More information about this and other discounts and sales charge waivers is available from your financial intermediary, in the Prospectus under the captions “Class A Sales Charge Waivers,” beginning on page 146, and “Appendix A – Sales Charge Waivers Offered by Financial Intermediaries,” beginning on page 200, and in the Statement of Additional Information under the caption “Additional Information Respecting Purchase and Redemption of Shares,” beginning on page 108.
Shareholder Fees Caption [Text] rr_ShareholderFeesCaption Shareholder Fees (fees paid directly from your investment)
Operating Expenses Caption [Text] rr_OperatingExpensesCaption Annual Fund Operating Expenses (expenses that you pay each year as a percentage of the value of your investment)
Fee Waiver or Reimbursement over Assets, Date of Termination rr_FeeWaiverOrReimbursementOverAssetsDateOfTermination February 1, 2023
Portfolio Turnover [Heading] rr_PortfolioTurnoverHeading Portfolio Turnover.
Portfolio Turnover [Text Block] rr_PortfolioTurnoverTextBlock

The Fund pays transaction costs, such as commissions, when it buys and sells securities (or “turns over”) its portfolio. A higher portfolio turnover rate may indicate higher transaction costs and may result in higher taxes when Fund shares are held in a taxable account. These costs, which are not reflected in Annual Fund Operating Expenses or in the Example, affect the Fund’s performance. During the most recent fiscal year, the Fund’s portfolio turnover rate was 10.43% of the average value of its portfolio.
Portfolio Turnover, Rate rr_PortfolioTurnoverRate 10.43%
Expense Breakpoint Discounts [Text] rr_ExpenseBreakpointDiscounts You may qualify for discounts from the sales charges applicable to Class A shares if you or other qualifying account holders invest, or agree to invest in the future, at least $50,000 in the Thornburg Funds.
Expense Breakpoint, Minimum Investment Required [Amount] rr_ExpenseBreakpointMinimumInvestmentRequiredAmount $ 50,000
Expense Example [Heading] rr_ExpenseExampleHeading Example.
Expense Example Narrative [Text Block] rr_ExpenseExampleNarrativeTextBlock

This Example is intended to help you compare the cost of investing in the Fund with the cost of investing in other mutual funds.

The Example assumes that you invest $10,000 in the Fund for the time periods indicated and then redeem all of your shares at the end of those periods. The Example also assumes that your investment has a 5% return each year, dividends and distributions are reinvested, and that the Fund’s operating expenses remain the same. Although your actual costs may be higher or lower, based on these assumptions (and giving effect to fee waivers and expense reimbursements in the first year), your costs would be:
Expense Example, No Redemption Narrative [Text Block] rr_ExpenseExampleNoRedemptionNarrativeTextBlock

You would pay the following expenses if you did not redeem your Class C shares:
Strategy [Heading] rr_StrategyHeading Principal Investment Strategies
Strategy Narrative [Text Block] rr_StrategyNarrativeTextBlock

Thornburg Investment Management, Inc. (“Thornburg”) actively manages the Fund’s investments in pursuing the Fund’s investment goal. The Fund invests principally in a portfolio of municipal obligations issued by states and state agencies, local governments and their agencies, and by United States territories and possessions. Investment decisions are based upon outlooks for interest rates and securities markets, the supply of municipal debt obligations, the difference in yields between higher and lower-rated obligations, and analysis of specific obligations. The Fund invests in obligations and participations in obligations of any credit quality. The Fund may invest up to 50 percent of its portfolio in lower-quality debt obligations rated by a nationally recognized statistical rating organization at the time of purchase as below investment grade (sometimes called “junk” bonds or “high yield” bonds) or, if unrated, issued by obligors which Thornburg determines have comparable below investment grade obligations outstanding or which are deemed by Thornburg to be comparable to obligors with outstanding below investment grade obligations. The Fund may also invest in obligations that are in default at the time of purchase. “Participations” are undivided interests in pools of securities where the underlying credit support passes through to the participants.

The Fund may invest in municipal obligations of any maturity, but seeks to maintain a portfolio of investments having a dollar-weighted average effective duration of normally one to ten years. Duration is a measure of estimated sensitivity to interest rate changes. A portfolio with a longer average effective duration will typically be more sensitive to interest rate changes than a portfolio with a shorter average effective duration. Duration is commonly expressed as a number, which is the expected percentage change in an obligation’s price upon a 1% change in interest rates. For example, an obligation with a duration of 10 would be expected to change in price by approximately 10% in response to a 1% change in interest rates. During temporary periods the Fund’s average effective duration and average portfolio maturity may be reduced for defensive purposes. There is no limitation on the duration or maturity of any specific security the Fund may purchase. The Fund may dispose of any security before it matures. The Fund attempts to reduce changes in its share value through credit analysis, selection and diversification.

The Fund ordinarily acquires and holds securities for investment rather than for realization of gains by short-term trading on market fluctuations. However, it may sell an investment prior to its scheduled maturity date to enhance income or reduce loss, to change the portfolio’s average duration or average maturity, to pursue other investment opportunities, in response to

changes in the conditions or business of the investment’s issuer or changes in overall market conditions, or if, in Thornburg’s opinion, the investment no longer serves to achieve the Fund’s investment goals.  The objective of preserving capital may prevent the Fund from obtaining the highest yields available.

The Fund normally invests 100% of its assets in municipal obligations, the income from which is exempt from the regular federal income tax. The Fund may invest up to 20% of its assets in taxable securities which would produce income not exempt from federal income tax because of market conditions, pending investment of idle funds or to afford liquidity. The Fund’s temporary taxable investments may exceed 20% of its assets when made for defensive purposes during periods of abnormal market conditions. If the Fund found it necessary to own taxable investments, some of its income would be subject to federal income tax. Gains realized on investments held by the Fund and not offset by realized losses will be subject to federal income tax.
Risk [Heading] rr_RiskHeading Principal Investment Risks
Risk Narrative [Text Block] rr_RiskNarrativeTextBlock

An investment in the Fund is not a deposit in any bank and is not insured or guaranteed by the Federal Deposit Insurance Corporation or any other government agency. Accordingly, the loss of money is a risk of investing in the Fund. The value of the Fund’s shares and its dividends may fluctuate from day to day and over time, and when you sell your shares they may be worth less than what you paid for them. The following is a summary of the principal risks of investing in the Fund. Please note that because the Fund’s objective is to provide high current income, the Fund invests with an emphasis on income, rather than stability of net asset value.

Management Risk – The Fund is an actively managed portfolio, and the value of the Fund may be reduced if Thornburg pursues unsuccessful investments or fails to correctly identify risks affecting the broad economy or specific issuers in which the Fund invests.

Interest Rate Risk – When interest rates increase, the value of the Fund’s investments may decline and the Fund’s share value may be reduced. This effect is typically more pronounced for intermediate and longer-term obligations. When interest rates decrease, the Fund’s dividends may decline. Decreases in market interest rates may also result in prepayments of obligations the Fund acquires, requiring the Fund to reinvest at lower interest rates.

Credit Risk – If obligations held by the Fund are downgraded by ratings agencies or go into default, or if legislation or other government action reduces the ability of issuers to pay principal and interest when due, the value of those obligations may decline and the Fund’s share value and the dividends paid by the Fund may be reduced. Because the ability of an issuer of a lower-rated or unrated obligation to pay principal and interest when due is typically less certain than for an issuer of a higher-rated obligation, lower-rated and unrated obligations are generally more vulnerable than higher-rated obligations to default, to ratings downgrades, and to liquidity risk. For example, municipal leases held by the Fund may be subject to non-appropriation provisions which permit governmental agencies or issuers to discontinue payments to the Fund under the municipal leases.

High Yield Risk – Debt obligations that are rated below investment grade and unrated obligations of similar credit quality (commonly referred to as “junk” or “high yield” bonds) may have a substantial risk of loss. These obligations are generally considered to be speculative with respect to the issuer’s ability to pay interest and principal when due. These obligations may be subject to greater price volatility than investment grade obligations, and their prices may decline significantly in periods of general economic difficulty or in response to adverse publicity, changes in investor perceptions or other factors. These obligations may also be subject to greater liquidity risk.

Market and Economic Risk – The value of the Fund’s investments may decline and its share value may be reduced due to changes in general economic and market conditions. This effect is typically more pronounced for the Fund’s investments in lower-rated and unrated municipal obligations (including particularly “junk” or “high yield” bonds), the value of which may fluctuate more significantly in response to poor economic growth or other changes in market conditions, political, economic and legal developments, and developments affecting specific issuers.

Liquidity Risk – Due to a lack of demand in the marketplace or other factors, the Fund may not be able to sell promptly some or all of the obligations that it holds, or may only be able to sell obligations at less than desired prices. The market for lower-rated and unrated obligations (including particularly “junk” or “high yield” bonds) may be less liquid than the market for other obligations, making it difficult for the Fund to value its investment in a lower-rated or unrated obligation or to sell the investment in a timely manner or at an acceptable price.

Cybersecurity and Operational Risk – Operational failures, cyber-attacks or other disruptions that affect the Fund’s service providers, the Fund’s counterparties, other market participants or the issuers of securities held by the Fund may adversely affect the Fund and its shareholders, including by causing losses for the Fund or impairing Fund operations.

Additional information about Fund investments, investment strategies and risks of investing in the Fund appears beginning on page 118 of the Prospectus.
Risk Lose Money [Text] rr_RiskLoseMoney Accordingly, the loss of money is a risk of investing in the Fund.
RIsk Not Insured [Text] rr_RiskNotInsured An investment in the Fund is not a deposit in any bank and is not insured or guaranteed by the Federal Deposit Insurance Corporation or any other government agency.
Bar Chart and Performance Table [Heading] rr_BarChartAndPerformanceTableHeading Past Performance of the Fund
Performance Narrative [Text Block] rr_PerformanceNarrativeTextBlock

The following information provides some indication of the risks of investing in Strategic Municipal Income Fund by showing how the Fund’s investment results vary from year to year. The bar chart shows how the annual total returns for Class A shares have been different in each full year shown. The average annual total return figures compare Class A, Class C and Class I share performance to the ICE BofAML US Municipal Master Index, a broad measure of market performance. Past performance (before and after taxes) is not necessarily an indication of how the Fund will perform in the future. The performance information shown is as of the calendar year ended December 31, 2021. Updated performance information may be obtained on the Thornburg website at Thornburg.com or by calling 1-800-847-0200.
Performance Information Illustrates Variability of Returns [Text] rr_PerformanceInformationIllustratesVariabilityOfReturns The following information provides some indication of the risks of investing in Strategic Municipal Income Fund by showing how the Fund’s investment results vary from year to year.
Performance Availability Phone [Text] rr_PerformanceAvailabilityPhone 1-800-847-0200
Performance Availability Website Address [Text] rr_PerformanceAvailabilityWebSiteAddress Thornburg.com
Performance Past Does Not Indicate Future [Text] rr_PerformancePastDoesNotIndicateFuture Past performance (before and after taxes) is not necessarily an indication of how the Fund will perform in the future.
Bar Chart [Heading] rr_BarChartHeading Annual Total Returns – Class A Shares
Bar Chart Does Not Reflect Sales Loads [Text] rr_BarChartDoesNotReflectSalesLoads The sales charge for Class A shares is not reflected in the returns shown in the bar chart above, and the returns would be less if the charge was taken into account.
Bar Chart Closing [Text Block] rr_BarChartClosingTextBlock

Total
Returns

Quarter
ended

Highest Quarterly Results

4.69%

6/30/2011

Lowest Quarterly Results

(3.57)%

12/31/2016

The sales charge for Class A shares is not reflected in the returns shown in the bar chart above, and the returns would be less if the charge was taken into account.
Performance Table Heading rr_PerformanceTableHeading Average Annual Total Returns (periods ended 12-31-21)
Performance Table Uses Highest Federal Rate rr_PerformanceTableUsesHighestFederalRate After-tax returns are calculated using the historical highest individual federal marginal income tax rates, and do not reflect state or local income taxes.
Performance Table Not Relevant to Tax Deferred rr_PerformanceTableNotRelevantToTaxDeferred Actual after-tax returns depend on an investor’s own tax situation and may differ from the returns shown, and after-tax returns shown are not relevant to investors who hold their Fund shares through tax-deferred arrangements, such as 401(k) plans or individual retirement accounts.
Performance Table One Class of after Tax Shown [Text] rr_PerformanceTableOneClassOfAfterTaxShown The after-tax returns shown relate only to Class A shares, and after-tax returns for other share classes will vary.
Performance Table Closing [Text Block] rr_PerformanceTableClosingTextBlock

After-tax returns are calculated using the historical highest individual federal marginal income tax rates, and do not reflect state or local income taxes. Actual after-tax returns depend on an investor’s own tax situation and may differ from the returns shown, and after-tax returns shown are not relevant to investors who hold their Fund shares through tax-deferred arrangements, such as 401(k) plans or individual retirement accounts. The after-tax returns shown relate only to Class A shares, and after-tax returns for other share classes will vary.
Retail | Thornburg Strategic Municipal Income Fund | Thornburg Strategic Municipal Income Fund Class A  
Prospectus [Line Items] rr_ProspectusLineItems  
Trading Symbol dei_TradingSymbol TSSAX
Maximum Sales Charge Imposed on Purchases (as a percentage of Offering Price) rr_MaximumSalesChargeImposedOnPurchasesOverOfferingPrice 2.00%
Maximum Deferred Sales Charge (as a percentage) rr_MaximumDeferredSalesChargeOverOther none [57]
Management Fees (as a percentage of Assets) rr_ManagementFeesOverAssets 0.75%
Distribution and Service (12b-1) Fees rr_DistributionAndService12b1FeesOverAssets 0.25%
Other Expenses (as a percentage of Assets): rr_OtherExpensesOverAssets 0.26%
Expenses (as a percentage of Assets) rr_ExpensesOverAssets 1.26%
Fee Waiver or Reimbursement rr_FeeWaiverOrReimbursementOverAssets (0.45%) [58]
Net Expenses (as a percentage of Assets) rr_NetExpensesOverAssets 0.81%
Expense Example, with Redemption, 1 Year rr_ExpenseExampleYear01 $ 281
Expense Example, with Redemption, 3 Years rr_ExpenseExampleYear03 548
Expense Example, with Redemption, 5 Years rr_ExpenseExampleYear05 835
Expense Example, with Redemption, 10 Years rr_ExpenseExampleYear10 $ 1,653
Annual Return 2012 rr_AnnualReturn2012 9.76%
Annual Return 2013 rr_AnnualReturn2013 (2.80%)
Annual Return 2014 rr_AnnualReturn2014 9.86%
Annual Return 2015 rr_AnnualReturn2015 2.23%
Annual Return 2016 rr_AnnualReturn2016 (0.38%)
Annual Return 2017 rr_AnnualReturn2017 4.04%
Annual Return 2018 rr_AnnualReturn2018 0.74%
Annual Return 2019 rr_AnnualReturn2019 5.59%
Annual Return 2020 rr_AnnualReturn2020 3.79%
Annual Return 2021 rr_AnnualReturn2021 1.22%
Highest Quarterly Return, Label rr_HighestQuarterlyReturnLabel Highest Quarterly Results
Highest Quarterly Return, Date rr_BarChartHighestQuarterlyReturnDate Jun. 30, 2011
Highest Quarterly Return rr_BarChartHighestQuarterlyReturn 4.69%
Lowest Quarterly Return, Label rr_LowestQuarterlyReturnLabel Lowest Quarterly Results
Lowest Quarterly Return, Date rr_BarChartLowestQuarterlyReturnDate Dec. 31, 2016
Lowest Quarterly Return rr_BarChartLowestQuarterlyReturn (3.57%)
1 Year rr_AverageAnnualReturnYear01 (0.83%)
5 Years rr_AverageAnnualReturnYear05 2.65%
10 Years rr_AverageAnnualReturnYear10 3.12%
Retail | Thornburg Strategic Municipal Income Fund | Thornburg Strategic Municipal Income Fund Class A | After Taxes on Distributions  
Prospectus [Line Items] rr_ProspectusLineItems  
1 Year rr_AverageAnnualReturnYear01 (0.83%)
5 Years rr_AverageAnnualReturnYear05 2.65%
10 Years rr_AverageAnnualReturnYear10 3.10%
Retail | Thornburg Strategic Municipal Income Fund | Thornburg Strategic Municipal Income Fund Class A | After Taxes on Distributions and Sales  
Prospectus [Line Items] rr_ProspectusLineItems  
1 Year rr_AverageAnnualReturnYear01 0.26%
5 Years rr_AverageAnnualReturnYear05 2.59%
10 Years rr_AverageAnnualReturnYear10 2.98%
Retail | Thornburg Strategic Municipal Income Fund | Thornburg Strategic Municipal Income Fund Class A | ICE BofAML US Municipal Master Index (reflects no deduction for fees, expenses, or taxes)  
Prospectus [Line Items] rr_ProspectusLineItems  
1 Year rr_AverageAnnualReturnYear01 1.83%
5 Years rr_AverageAnnualReturnYear05 4.23%
10 Years rr_AverageAnnualReturnYear10 3.88%
Retail | Thornburg Strategic Municipal Income Fund | Thornburg Strategic Municipal Income Fund Class C  
Prospectus [Line Items] rr_ProspectusLineItems  
Trading Symbol dei_TradingSymbol TSSCX
Maximum Sales Charge Imposed on Purchases (as a percentage of Offering Price) rr_MaximumSalesChargeImposedOnPurchasesOverOfferingPrice none
Maximum Deferred Sales Charge (as a percentage) rr_MaximumDeferredSalesChargeOverOther 0.60% [59]
Management Fees (as a percentage of Assets) rr_ManagementFeesOverAssets 0.75%
Distribution and Service (12b-1) Fees rr_DistributionAndService12b1FeesOverAssets 0.60%
Other Expenses (as a percentage of Assets): rr_OtherExpensesOverAssets 0.36%
Expenses (as a percentage of Assets) rr_ExpensesOverAssets 1.71%
Fee Waiver or Reimbursement rr_FeeWaiverOrReimbursementOverAssets (0.43%) [58]
Net Expenses (as a percentage of Assets) rr_NetExpensesOverAssets 1.28%
Expense Example, with Redemption, 1 Year rr_ExpenseExampleYear01 $ 190
Expense Example, with Redemption, 3 Years rr_ExpenseExampleYear03 497
Expense Example, with Redemption, 5 Years rr_ExpenseExampleYear05 888
Expense Example, with Redemption, 10 Years rr_ExpenseExampleYear10 1,984
Expense Example, No Redemption, 1 Year rr_ExpenseExampleNoRedemptionYear01 130
Expense Example, No Redemption, 3 Years rr_ExpenseExampleNoRedemptionYear03 497
Expense Example, No Redemption, 5 Years rr_ExpenseExampleNoRedemptionYear05 888
Expense Example, No Redemption, 10 Years rr_ExpenseExampleNoRedemptionYear10 $ 1,984
1 Year rr_AverageAnnualReturnYear01 0.21%
5 Years rr_AverageAnnualReturnYear05 2.57%
10 Years rr_AverageAnnualReturnYear10 2.94%
Retail | Thornburg Strategic Municipal Income Fund | Thornburg Strategic Municipal Income Fund Class C | ICE BofAML US Municipal Master Index (reflects no deduction for fees, expenses, or taxes)  
Prospectus [Line Items] rr_ProspectusLineItems  
1 Year rr_AverageAnnualReturnYear01 1.83%
5 Years rr_AverageAnnualReturnYear05 4.23%
10 Years rr_AverageAnnualReturnYear10 3.88%
Retail | Thornburg Strategic Municipal Income Fund | Thornburg Strategic Municipal Income Fund Class I  
Prospectus [Line Items] rr_ProspectusLineItems  
Trading Symbol dei_TradingSymbol TSSIX
Maximum Sales Charge Imposed on Purchases (as a percentage of Offering Price) rr_MaximumSalesChargeImposedOnPurchasesOverOfferingPrice none
Maximum Deferred Sales Charge (as a percentage) rr_MaximumDeferredSalesChargeOverOther none
Management Fees (as a percentage of Assets) rr_ManagementFeesOverAssets 0.75%
Distribution and Service (12b-1) Fees rr_DistributionAndService12b1FeesOverAssets none
Other Expenses (as a percentage of Assets): rr_OtherExpensesOverAssets 0.22%
Expenses (as a percentage of Assets) rr_ExpensesOverAssets 0.97%
Fee Waiver or Reimbursement rr_FeeWaiverOrReimbursementOverAssets (0.38%) [58]
Net Expenses (as a percentage of Assets) rr_NetExpensesOverAssets 0.59%
Expense Example, with Redemption, 1 Year rr_ExpenseExampleYear01 $ 60
Expense Example, with Redemption, 3 Years rr_ExpenseExampleYear03 271
Expense Example, with Redemption, 5 Years rr_ExpenseExampleYear05 499
Expense Example, with Redemption, 10 Years rr_ExpenseExampleYear10 $ 1,155
1 Year rr_AverageAnnualReturnYear01 1.50%
5 Years rr_AverageAnnualReturnYear05 3.29%
10 Years rr_AverageAnnualReturnYear10 3.61%
Retail | Thornburg Strategic Municipal Income Fund | Thornburg Strategic Municipal Income Fund Class I | ICE BofAML US Municipal Master Index (reflects no deduction for fees, expenses, or taxes)  
Prospectus [Line Items] rr_ProspectusLineItems  
1 Year rr_AverageAnnualReturnYear01 1.83%
5 Years rr_AverageAnnualReturnYear05 4.23%
10 Years rr_AverageAnnualReturnYear10 3.88%
Retirement | Thornburg Global Opportunities Fund  
Prospectus [Line Items] rr_ProspectusLineItems  
Risk/Return [Heading] rr_RiskReturnHeading Global Opportunities Fund
Objective [Heading] rr_ObjectiveHeading Investment Goal
Objective, Primary [Text Block] rr_ObjectivePrimaryTextBlock

The Fund seeks long-term capital appreciation by investing in equity and debt securities of all types from issuers around the world.
Expense [Heading] rr_ExpenseHeading Fees and Expenses of the Fund
Expense Narrative [Text Block] rr_ExpenseNarrativeTextBlock

This table describes the fees and expenses that you may pay if you buy and hold shares of the Fund.
Shareholder Fees Caption [Text] rr_ShareholderFeesCaption Shareholder Fees (fees paid directly from your investment)
Operating Expenses Caption [Text] rr_OperatingExpensesCaption Annual Fund Operating Expenses (expenses that you pay each year as a percentage of the value of your investment)
Fee Waiver or Reimbursement over Assets, Date of Termination rr_FeeWaiverOrReimbursementOverAssetsDateOfTermination February 1, 2023
Portfolio Turnover [Heading] rr_PortfolioTurnoverHeading Portfolio Turnover.
Portfolio Turnover [Text Block] rr_PortfolioTurnoverTextBlock

The Fund pays transaction costs, such as commissions, when it buys and sells securities (or “turns over”) its portfolio. A higher portfolio turnover rate may indicate higher transaction costs and may result in higher taxes when Fund shares are held in a taxable account. These costs, which are not reflected in Annual Fund Operating Expenses or in the Example, affect the Fund’s performance. During the most recent fiscal year, the Fund’s portfolio turnover rate was 25.48% of the average value of its portfolio.
Portfolio Turnover, Rate rr_PortfolioTurnoverRate 25.48%
Expense Example [Heading] rr_ExpenseExampleHeading Example.
Expense Example Narrative [Text Block] rr_ExpenseExampleNarrativeTextBlock

This Example is intended to help you compare the cost of investing in the Fund with the cost of investing in other mutual funds.

The Example assumes that you invest $10,000 in the Fund for the time periods indicated and then redeem all of your shares at the end of those periods. The Example also assumes that your investment has a 5% return each year, dividends and distributions are reinvested, and that the Fund’s operating expenses remain the same. Although your actual costs may be higher or lower, based on these assumptions (and giving effect to fee waivers and expense reimbursements in the first year), your costs would be:
Strategy [Heading] rr_StrategyHeading Principal Investment Strategies
Strategy Narrative [Text Block] rr_StrategyNarrativeTextBlock

The Fund pursues its investment goal by investing primarily in a broad range of equity securities, including common stocks, preferred stocks and publicly traded real estate investment trusts. The Fund may invest in any stock or other equity security which its investment advisor, Thornburg Investment Management, Inc. (“Thornburg”), believes may assist the Fund in pursuing its goal, including smaller companies with market capitalizations of less than $500 million.

The Fund portfolio includes investments in both domestic securities and securities of issuers domiciled in or economically tied to countries outside the United States, including developing countries. Relative proportions of each will vary from time to time, depending upon the advisor’s view of specific investment opportunities and macro-economic factors. Under normal market conditions, the Fund invests a significant portion of its assets in issuers domiciled in or economically tied to countries outside the United States.

The Fund’s investments are determined by individual issuer and industry analysis. Investment decisions are based on domestic and international economic developments, outlooks for securities markets, interest rates and inflation, the supply and demand for securities, and analysis of specific issuers.

The Fund may sell an investment if Thornburg has identified a better investment opportunity, in response to changes in the conditions or business of the investment’s issuer or changes in overall market conditions, if Thornburg has a target price for the investment and that target price has been achieved, or if, in Thornburg’s opinion, the investment no longer serves to achieve the Fund’s investment goals.
Risk [Heading] rr_RiskHeading Principal Investment Risks
Risk Narrative [Text Block] rr_RiskNarrativeTextBlock

An investment in the Fund is not a deposit in any bank and is not insured or guaranteed by the Federal Deposit Insurance Corporation or any other governmental agency. Accordingly, the loss of money is a risk of investing in the Fund. The value of the Fund’s shares varies from day to day and over time, and when you sell your shares they may be worth less than what you paid for them. The following is a summary of the principal risks of investing in the Fund.

Management Risk – The Fund is an actively managed portfolio, and the value of the Fund may be reduced if Thornburg pursues unsuccessful investments or fails to correctly identify risks affecting the broad economy or specific issuers in which the Fund invests.

Market and Economic Risk – The value of the Fund’s investments may decline and its share value may be reduced due to changes in general economic and market conditions. The value of a security may change in response to developments affecting entire economies, markets or industries, including changes in interest rates, political and legal developments, and general market volatility.

Equity Risk – The value of the Fund’s equity investments may fluctuate significantly over time in response to factors affecting individual issuers, particular industries, or the market as a whole. Additionally, common stock ranks below preferred stock and debt securities in claims for dividends and for assets of a company in a liquidation or bankruptcy.

Risks Affecting Specific Issuers – The value of a security may decline in response to developments affecting the specific issuer of the security, even if the overall industry or economy is unaffected. These developments may include a variety of factors, including but not limited to management issues or other corporate disruption, a decline in revenues or profitability, an increase in costs, or an adverse effect on the issuer’s competitive position.

Foreign Investment Risk – Investments in securities of foreign issuers may involve risks including adverse fluctuations in currency exchange rates, political instability, confiscations, taxes or restrictions on currency exchange, difficulty in selling foreign investments, and reduced legal protection.

Developing Country Risk – The risks which may affect investments in foreign issuers (see “Foreign Investment Risk,” above) may be more pronounced for investments in developing countries because the economies of those countries are usually less diversified, communications, transportation and economic infrastructures are less developed, and developing countries ordinarily have less established legal, political, business and social frameworks. At times the prices of equity securities of a developing country issuer may be extremely volatile. An issuer domiciled in a developed country may be similarly affected by these developing country risks to the extent that the issuer conducts its business in developing countries.

Foreign Currency Risk – Fluctuations in currency exchange rates can adversely affect the value of the Fund’s foreign investments. Such fluctuations may occur for a number of reasons, including market and economic conditions, or a government’s decision to devalue its currency or impose currency controls.

Risks Affecting Specific Countries or Regions – If a significant portion of the Fund’s assets is invested in issuers that are economically exposed to one country or region, the Fund’s share value may be more susceptible to the conditions and developments in that country or region, and potentially more volatile than the share value of a more geographically diversified fund. A specific country or region could also be adversely affected by conditions or developments arising in other countries. For example, the U.S. government could take actions to prohibit or restrict individuals or companies within the U.S. from purchasing or holding the shares of issuers in another country, which may limit the Fund’s ability to invest in that country or cause the Fund to have to sell investments in that country at less than desired prices. The nature and degree of the risks affecting a given country or region, and the extent of the Fund’s exposure to any such country or region, is expected to vary over time.

Small and Mid-Cap Company Risk – Investments in small-capitalization companies and mid-capitalization companies may involve additional risks, which may be relatively higher with smaller companies. These additional risks may result from limited product lines, more limited access to markets and financial resources, greater vulnerability to competition and changes in markets, lack of management depth, increased volatility in share price, and possible difficulties in valuing or selling these investments.

Credit Risk – The inability of an issuer to pay principal and interest on its debt obligations when due, or the downgrading of an issuer’s debt obligations by ratings agencies, may adversely affect the market’s perceptions of the issuer’s financial strength and may therefore result in declines in the issuer’s stock price.

Liquidity Risk – Due to a lack of demand in the marketplace or other factors, the Fund may not be able to sell some or all of its investments promptly, or may only be able to sell investments at less than desired prices. This risk may be more pronounced for the Fund’s investments in developing countries.

Real Estate Risk – The Fund’s investments in publicly traded real estate investment trusts (“REITs”) are subject to risks affecting real estate investments generally (including market conditions, competition, property obsolescence, changes in interest rates and casualty to real estate), as well as risks specifically affecting REITs (the quality and skill of REIT management and the internal expenses of the REIT).

 

Cybersecurity and Operational Risk – Operational failures, cyber-attacks or other disruptions that affect the Fund’s service providers, the Fund’s counterparties, other market participants or the issuers of securities held by the Fund may adversely affect the Fund and its shareholders, including by causing losses for the Fund or impairing Fund operations.

Additional information about Fund investments, investment strategies and risks of investing in the Fund appears below beginning on page 61 of the Prospectus.
Risk Lose Money [Text] rr_RiskLoseMoney Accordingly, the loss of money is a risk of investing in the Fund.
RIsk Not Insured [Text] rr_RiskNotInsured An investment in the Fund is not a deposit in any bank and is not insured or guaranteed by the Federal Deposit Insurance Corporation or any other governmental agency.
Bar Chart and Performance Table [Heading] rr_BarChartAndPerformanceTableHeading Past Performance of the Fund
Performance Narrative [Text Block] rr_PerformanceNarrativeTextBlock

The following information provides some indication of the risks of investing in Global Opportunities Fund by showing how the Fund’s investment results vary from year to year. The bar chart shows how the annual total returns for Class R3 shares of the Fund vary in each full year shown. The average annual total return figures compare Class R3, Class R4, Class R5 and Class R6 share performance to the MSCI ACWI Net Total Return USD Index, which represents a broad measure of both domestic and foreign equity market performance. Past performance (before and after taxes) is not necessarily an indication of how the Fund will perform in the future. The performance information shown below is as of the calendar year ended December 31, 2021. Updated performance information may be obtained on the Thornburg website at www.thornburg.com or by calling 1-800-847-0200.
Performance Information Illustrates Variability of Returns [Text] rr_PerformanceInformationIllustratesVariabilityOfReturns The following information provides some indication of the risks of investing in Global Opportunities Fund by showing how the Fund’s investment results vary from year to year.
Performance Availability Phone [Text] rr_PerformanceAvailabilityPhone 1-800-847-0200
Performance Availability Website Address [Text] rr_PerformanceAvailabilityWebSiteAddress www.thornburg.com
Performance Past Does Not Indicate Future [Text] rr_PerformancePastDoesNotIndicateFuture Past performance (before and after taxes) is not necessarily an indication of how the Fund will perform in the future.
Bar Chart [Heading] rr_BarChartHeading Annual Total Returns – Class R3 Shares
Bar Chart Closing [Text Block] rr_BarChartClosingTextBlock

Total
Returns

Quarter
ended

Highest Quarterly Results

21.70%

6/30/2020

Lowest Quarterly Results

(24.86)%

3/31/2020
Performance Table Heading rr_PerformanceTableHeading Average Annual Total Returns (periods ended 12-31-21)
Performance Table Uses Highest Federal Rate rr_PerformanceTableUsesHighestFederalRate After-tax returns are calculated using the highest historical individual federal marginal income tax rates, and do not reflect state or local income taxes.
Performance Table Not Relevant to Tax Deferred rr_PerformanceTableNotRelevantToTaxDeferred Actual after-tax returns depend on an investor’s own tax situation and may differ from the returns shown, and after-tax returns shown are not relevant to investors who hold their Fund shares through tax-deferred arrangements, such as 401(k) plans or individual retirement accounts.
Performance Table One Class of after Tax Shown [Text] rr_PerformanceTableOneClassOfAfterTaxShown The after-tax returns shown relate only to Class R3 shares, and after-tax returns for other share classes will vary.
Performance Table Closing [Text Block] rr_PerformanceTableClosingTextBlock

After-tax returns are calculated using the highest historical individual federal marginal income tax rates, and do not reflect state or local income taxes. Actual after-tax returns depend on an investor’s own tax situation and may differ from the returns shown, and after-tax returns shown are not relevant to investors who hold their Fund shares through tax-deferred arrangements, such as 401(k) plans or individual retirement accounts. The after-tax returns shown relate only to Class R3 shares, and after-tax returns for other share classes will vary.
Retirement | Thornburg Global Opportunities Fund | Thornburg Global Opportunities Fund - Class R3  
Prospectus [Line Items] rr_ProspectusLineItems  
Trading Symbol dei_TradingSymbol THORX
Maximum Sales Charge Imposed on Purchases (as a percentage of Offering Price) rr_MaximumSalesChargeImposedOnPurchasesOverOfferingPrice none
Maximum Deferred Sales Charge (as a percentage) rr_MaximumDeferredSalesChargeOverOther none
Management Fees (as a percentage of Assets) rr_ManagementFeesOverAssets 0.85%
Distribution and Service (12b-1) Fees rr_DistributionAndService12b1FeesOverAssets 0.50%
Other Expenses (as a percentage of Assets): rr_OtherExpensesOverAssets 0.72%
Expenses (as a percentage of Assets) rr_ExpensesOverAssets 2.07%
Fee Waiver or Reimbursement rr_FeeWaiverOrReimbursementOverAssets (0.57%) [60]
Net Expenses (as a percentage of Assets) rr_NetExpensesOverAssets 1.50%
Expense Example, with Redemption, 1 Year rr_ExpenseExampleYear01 $ 153
Expense Example, with Redemption, 3 Years rr_ExpenseExampleYear03 594
Expense Example, with Redemption, 5 Years rr_ExpenseExampleYear05 1,061
Expense Example, with Redemption, 10 Years rr_ExpenseExampleYear10 $ 2,355
Annual Return 2012 rr_AnnualReturn2012 21.62%
Annual Return 2013 rr_AnnualReturn2013 28.07%
Annual Return 2014 rr_AnnualReturn2014 18.31%
Annual Return 2015 rr_AnnualReturn2015 0.95%
Annual Return 2016 rr_AnnualReturn2016 3.49%
Annual Return 2017 rr_AnnualReturn2017 21.37%
Annual Return 2018 rr_AnnualReturn2018 (21.07%)
Annual Return 2019 rr_AnnualReturn2019 28.09%
Annual Return 2020 rr_AnnualReturn2020 22.05%
Annual Return 2021 rr_AnnualReturn2021 14.18%
Highest Quarterly Return, Label rr_HighestQuarterlyReturnLabel Highest Quarterly Results
Highest Quarterly Return, Date rr_BarChartHighestQuarterlyReturnDate Jun. 30, 2020
Highest Quarterly Return rr_BarChartHighestQuarterlyReturn 21.70%
Lowest Quarterly Return, Label rr_LowestQuarterlyReturnLabel Lowest Quarterly Results
Lowest Quarterly Return, Date rr_BarChartLowestQuarterlyReturnDate Mar. 31, 2020
Lowest Quarterly Return rr_BarChartLowestQuarterlyReturn (24.86%)
1 Year rr_AverageAnnualReturnYear01 14.18%
5 Years rr_AverageAnnualReturnYear05 11.33%
10 Years rr_AverageAnnualReturnYear10 12.66%
Retirement | Thornburg Global Opportunities Fund | Thornburg Global Opportunities Fund - Class R3 | After Taxes on Distributions  
Prospectus [Line Items] rr_ProspectusLineItems  
1 Year rr_AverageAnnualReturnYear01 10.57%
5 Years rr_AverageAnnualReturnYear05 9.93%
10 Years rr_AverageAnnualReturnYear10 11.85%
Retirement | Thornburg Global Opportunities Fund | Thornburg Global Opportunities Fund - Class R3 | After Taxes on Distributions and Sales  
Prospectus [Line Items] rr_ProspectusLineItems  
1 Year rr_AverageAnnualReturnYear01 10.58%
5 Years rr_AverageAnnualReturnYear05 8.71%
10 Years rr_AverageAnnualReturnYear10 10.39%
Retirement | Thornburg Global Opportunities Fund | Thornburg Global Opportunities Fund - Class R3 | MSCI AC World Index (reflects no deduction for fees, expenses, or U.S. taxes)  
Prospectus [Line Items] rr_ProspectusLineItems  
1 Year rr_AverageAnnualReturnYear01 18.54%
5 Years rr_AverageAnnualReturnYear05 14.40%
10 Years rr_AverageAnnualReturnYear10 11.85%
Retirement | Thornburg Global Opportunities Fund | Thornburg Global Opportunities Fund - Class R4  
Prospectus [Line Items] rr_ProspectusLineItems  
Trading Symbol dei_TradingSymbol THOVX
Maximum Sales Charge Imposed on Purchases (as a percentage of Offering Price) rr_MaximumSalesChargeImposedOnPurchasesOverOfferingPrice none
Maximum Deferred Sales Charge (as a percentage) rr_MaximumDeferredSalesChargeOverOther none
Management Fees (as a percentage of Assets) rr_ManagementFeesOverAssets 0.85%
Distribution and Service (12b-1) Fees rr_DistributionAndService12b1FeesOverAssets 0.25%
Other Expenses (as a percentage of Assets): rr_OtherExpensesOverAssets 0.73%
Expenses (as a percentage of Assets) rr_ExpensesOverAssets 1.83%
Fee Waiver or Reimbursement rr_FeeWaiverOrReimbursementOverAssets (0.43%) [60]
Net Expenses (as a percentage of Assets) rr_NetExpensesOverAssets 1.40%
Expense Example, with Redemption, 1 Year rr_ExpenseExampleYear01 $ 143
Expense Example, with Redemption, 3 Years rr_ExpenseExampleYear03 534
Expense Example, with Redemption, 5 Years rr_ExpenseExampleYear05 950
Expense Example, with Redemption, 10 Years rr_ExpenseExampleYear10 $ 2,113
1 Year rr_AverageAnnualReturnYear01 14.28%
5 Years rr_AverageAnnualReturnYear05 11.44%
10 Years rr_AverageAnnualReturnYear10 12.76%
Retirement | Thornburg Global Opportunities Fund | Thornburg Global Opportunities Fund - Class R4 | MSCI AC World Index (reflects no deduction for fees, expenses, or U.S. taxes)  
Prospectus [Line Items] rr_ProspectusLineItems  
1 Year rr_AverageAnnualReturnYear01 18.54%
5 Years rr_AverageAnnualReturnYear05 14.40%
10 Years rr_AverageAnnualReturnYear10 11.85%
Retirement | Thornburg Global Opportunities Fund | Thornburg Global Opportunities Fund - Class R5  
Prospectus [Line Items] rr_ProspectusLineItems  
Trading Symbol dei_TradingSymbol THOFX
Maximum Sales Charge Imposed on Purchases (as a percentage of Offering Price) rr_MaximumSalesChargeImposedOnPurchasesOverOfferingPrice none
Maximum Deferred Sales Charge (as a percentage) rr_MaximumDeferredSalesChargeOverOther none
Management Fees (as a percentage of Assets) rr_ManagementFeesOverAssets 0.85%
Distribution and Service (12b-1) Fees rr_DistributionAndService12b1FeesOverAssets none
Other Expenses (as a percentage of Assets): rr_OtherExpensesOverAssets 0.51%
Expenses (as a percentage of Assets) rr_ExpensesOverAssets 1.36%
Fee Waiver or Reimbursement rr_FeeWaiverOrReimbursementOverAssets (0.37%) [60]
Net Expenses (as a percentage of Assets) rr_NetExpensesOverAssets 0.99%
Expense Example, with Redemption, 1 Year rr_ExpenseExampleYear01 $ 101
Expense Example, with Redemption, 3 Years rr_ExpenseExampleYear03 394
Expense Example, with Redemption, 5 Years rr_ExpenseExampleYear05 709
Expense Example, with Redemption, 10 Years rr_ExpenseExampleYear10 $ 1,603
1 Year rr_AverageAnnualReturnYear01 14.73%
5 Years rr_AverageAnnualReturnYear05 11.89%
10 Years rr_AverageAnnualReturnYear10 13.22%
Retirement | Thornburg Global Opportunities Fund | Thornburg Global Opportunities Fund - Class R5 | MSCI AC World Index (reflects no deduction for fees, expenses, or U.S. taxes)  
Prospectus [Line Items] rr_ProspectusLineItems  
1 Year rr_AverageAnnualReturnYear01 18.54%
5 Years rr_AverageAnnualReturnYear05 14.40%
10 Years rr_AverageAnnualReturnYear10 11.85%
Retirement | Thornburg Global Opportunities Fund | Thornburg Global Opportunities Fund - Class R6  
Prospectus [Line Items] rr_ProspectusLineItems  
Trading Symbol dei_TradingSymbol THOGX
Maximum Sales Charge Imposed on Purchases (as a percentage of Offering Price) rr_MaximumSalesChargeImposedOnPurchasesOverOfferingPrice none
Maximum Deferred Sales Charge (as a percentage) rr_MaximumDeferredSalesChargeOverOther none
Management Fees (as a percentage of Assets) rr_ManagementFeesOverAssets 0.85%
Distribution and Service (12b-1) Fees rr_DistributionAndService12b1FeesOverAssets none
Other Expenses (as a percentage of Assets): rr_OtherExpensesOverAssets 0.15%
Expenses (as a percentage of Assets) rr_ExpensesOverAssets 1.00%
Fee Waiver or Reimbursement rr_FeeWaiverOrReimbursementOverAssets (0.15%) [60]
Net Expenses (as a percentage of Assets) rr_NetExpensesOverAssets 0.85%
Expense Example, with Redemption, 1 Year rr_ExpenseExampleYear01 $ 87
Expense Example, with Redemption, 3 Years rr_ExpenseExampleYear03 303
Expense Example, with Redemption, 5 Years rr_ExpenseExampleYear05 538
Expense Example, with Redemption, 10 Years rr_ExpenseExampleYear10 $ 1,211
1 Year rr_AverageAnnualReturnYear01 14.91%
Since Inception rr_AverageAnnualReturnSinceInception 11.00%
Inception Date rr_AverageAnnualReturnInceptionDate Apr. 10, 2017
Retirement | Thornburg Global Opportunities Fund | Thornburg Global Opportunities Fund - Class R6 | MSCI AC World Index (reflects no deduction for fees, expenses, or U.S. taxes)  
Prospectus [Line Items] rr_ProspectusLineItems  
1 Year rr_AverageAnnualReturnYear01 18.54%
Since Inception rr_AverageAnnualReturnSinceInception 13.74%
Retirement | Thornburg International Equity Fund  
Prospectus [Line Items] rr_ProspectusLineItems  
Risk/Return [Heading] rr_RiskReturnHeading International Equity Fund
Objective [Heading] rr_ObjectiveHeading Investment Goal
Objective, Primary [Text Block] rr_ObjectivePrimaryTextBlock

The Fund seeks long-term capital appreciation by investing in equity and debt securities of all types. The goal of the Fund is to seek some current income.

Expense [Heading] rr_ExpenseHeading Fees and Expenses of the Fund
Expense Narrative [Text Block] rr_ExpenseNarrativeTextBlock

This table describes the fees and expenses that you may pay if you buy and hold shares of the Fund.
Shareholder Fees Caption [Text] rr_ShareholderFeesCaption Shareholder Fees (fees paid directly from your investment)
Operating Expenses Caption [Text] rr_OperatingExpensesCaption Annual Fund Operating Expenses (expenses that you pay each year as a percentage of the value of your investment)
Fee Waiver or Reimbursement over Assets, Date of Termination rr_FeeWaiverOrReimbursementOverAssetsDateOfTermination February 1, 2023
Portfolio Turnover [Heading] rr_PortfolioTurnoverHeading Portfolio Turnover.
Portfolio Turnover [Text Block] rr_PortfolioTurnoverTextBlock

The Fund pays transaction costs, such as commissions, when it buys and sells securities (or “turns over”) its portfolio. A higher portfolio turnover rate may indicate higher transaction costs and may result in higher taxes when Fund shares are held in a taxable account. These costs, which are not reflected in Annual Fund Operating Expenses or in the Example, affect the Fund’s performance. During the most recent fiscal year, the Fund’s portfolio turnover rate was 42.85% of the average value of its portfolio.
Portfolio Turnover, Rate rr_PortfolioTurnoverRate 42.85%
Expense Example [Heading] rr_ExpenseExampleHeading Example.
Expense Example Narrative [Text Block] rr_ExpenseExampleNarrativeTextBlock

This Example is intended to help you compare the cost of investing in the Fund with the cost of investing in other mutual funds.

The Example assumes that you invest $10,000 in the Fund for the time periods indicated and then redeem all of your shares at the end of those periods. The Example also assumes that your investment has a 5% return each year, dividends and distributions are reinvested, and that the Fund’s operating expenses remain the same. Although your actual costs may be higher or lower, based on these assumptions (and giving effect to fee waivers and expense reimbursements in the first year), your costs would be:
Strategy [Heading] rr_StrategyHeading Principal Investment Strategies
Strategy Narrative [Text Block] rr_StrategyNarrativeTextBlock

The Fund invests primarily in common stocks of non-U.S. companies and depositary receipts associated with such stocks. The Fund may invest in developing countries, but under normal conditions those investments are expected to comprise a smaller proportion of the Fund than investments in developed countries. Under normal conditions, the Fund will invest at least 80% of its net assets in common stocks or depositary receipts.

The Fund’s investment advisor, Thornburg Investment Management, Inc. (“Thornburg”), intends to invest on an opportunistic basis where the Fund’s portfolio managers believe intrinsic value is not recognized by the marketplace. The Fund seeks to identify value in a broad or different context by investing in a diversified portfolio of stocks the Fund categorizes as basic values, consistent earners, and emerging franchises, when the portfolio managers believe these issues are value priced. The relative proportions of securities invested in each of those categories will vary over time. The Fund seeks to invest in promising companies, and may invest in stocks that reflect unfavorable market perceptions of the company or industry fundamentals. The Fund may invest in companies of any size, but invests primarily in the large and middle capitalization range of publicly traded companies.

Thornburg primarily uses individual issuer and industry analysis to make investment decisions. Value, for purposes of the Fund’s selection criteria, may consider both current and projected measures. Among the specific factors considered by Thornburg in identifying securities for inclusion in the Fund are:

•profitability

•price/earnings ratio

•price/book value ratio

•price/cash flow ratio

•debt/capital ratio

•dividend characteristics

•security and consistency of revenues

•EV (enterprise value)/EBITDA (earnings before interest, taxes, depreciation and amortization) ratio

•undervalued assets

•earnings growth potential

•industry growth characteristics

•industry leadership

•franchise value

•potential for favorable developments

•EBIT (earnings before interest and taxes)/interest expense ratio

The Fund categorizes its equity investments in the following three categories:

Basic Value: Companies generally operating in mature or cyclical industries and which generally exhibit more economic sensitivity and/or higher volatility in earnings and cash flow.

Consistent Earner: Companies which generally exhibit predictable growth, profitability, cash flow and/or dividends.

Emerging Franchise: Companies with the potential to grow at an above average rate because of a product or service that is establishing a new market and/or taking share from existing participants.

Inclusion of any investment in any of the three described categories represents the opinion of the advisor concerning the characteristics and prospects of the investment. There is no assurance that any company selected for investment will, once categorized in one of the three described investment categories, continue to have the positive characteristics or fulfill the expectations that the advisor had for the company when it was selected for investment, and any such company may not grow or may decline in earnings and size.

The Fund may sell an investment if Thornburg has identified a better investment opportunity, in response to changes in the conditions or business of the investment’s issuer or changes in overall market conditions, if Thornburg has a target price for the investment and that target price has been achieved, or if, in Thornburg’s opinion, the investment no longer serves to achieve the Fund’s investment goals.

The Fund’s policy of investing at least 80% of its net assets in common stocks or depositary receipts may be changed by the Fund’s Trustees without a shareholder vote upon 60 days’ notice to shareholders.
Risk [Heading] rr_RiskHeading Principal Investment Risks
Risk Narrative [Text Block] rr_RiskNarrativeTextBlock

An investment in the Fund is not a deposit in any bank and is not insured or guaranteed by the Federal Deposit Insurance Corporation or any other governmental agency. Accordingly, the loss of money is a risk of investing in the Fund. The value of the Fund’s shares varies from day to day and over time, and when you sell your shares they may be worth less than what you paid for them. The following is a summary of the principal risks of investing in the Fund.

Management Risk – The Fund is an actively managed portfolio, and the value of the Fund may be reduced if Thornburg pursues unsuccessful investments or fails to correctly identify risks affecting the broad economy or specific issuers in which the Fund invests.

Market and Economic Risk – The value of the Fund’s investments may decline and its share value may be reduced due to changes in general economic and market conditions. The value of a security may change in response to developments affecting entire economies, markets or industries, including changes in interest rates, political and legal developments, and general market volatility.

Equity Risk – The value of the Fund’s equity investments may fluctuate significantly over time in response to factors affecting individual issuers, particular industries, or the market as a whole. Additionally, common stock ranks below preferred stock and debt securities in claims for dividends and for assets of a company in a liquidation or bankruptcy.

Risks Affecting Specific Issuers – The value of a security may decline in response to developments affecting the specific issuer of the security, even if the overall industry or economy is unaffected. These developments may include a variety of factors, including but not limited to management issues or other corporate disruption, a decline in revenues or profitability, an increase in costs, or an adverse effect on the issuer’s competitive position.

Foreign Investment Risk – Investments in securities of foreign issuers may involve risks including adverse fluctuations in currency exchange rates, political instability, confiscations, taxes or restrictions on currency exchange, difficulty in selling foreign investments, and reduced legal protection.

Developing Country Risk – The risks which may affect investments in foreign issuers (see “Foreign Investment Risk,” above) may be more pronounced for investments in developing countries because the economies of those countries are usually less diversified, communications, transportation and economic infrastructures are less developed, and developing countries ordinarily have less established legal, political, business and social frameworks. At times the prices of equity securities of a developing country issuer may be extremely volatile. An issuer domiciled in a developed country may be similarly affected by these developing country risks to the extent that the issuer conducts its business in developing countries.

Foreign Currency Risk – Fluctuations in currency exchange rates can adversely affect the value of the Fund’s foreign investments. Such fluctuations may occur for a number of reasons, including market and economic conditions, or a government’s decision to devalue its currency or impose currency controls.

Risks Affecting Specific Countries or Regions – If a significant portion of the Fund’s assets is invested in issuers that are economically exposed to one country or region, the Fund’s share value may be more susceptible to the conditions and developments in that country or region, and potentially more volatile than the share value of a more geographically diversified fund. A specific country or region could also be adversely affected by conditions or developments arising in other countries. For example, the U.S. government could take actions to prohibit or restrict individuals or companies within the U.S. from purchasing or holding the shares of issuers in another country, which may limit the Fund’s ability to invest in that country or cause the Fund to have to sell investments in that country at less than desired prices. The nature and degree of the risks affecting a given country or region, and the extent of the Fund’s exposure to any such country or region, is expected to vary over time.

Risks Affecting Investments in China – A significant portion of the Fund’s assets may be invested in companies exposed to China. Risks affecting investments in China include a potential downturn in the Chinese economy, reduced liquidity or increased price volatility in the Chinese securities markets as a result of trading suspensions affecting Chinese issuers or other factors, the potential that the Chinese government may expand restrictions on foreign investments or the repatriation of capital, and the implementation of new tariffs or other trade barriers by China or its trading partners. A lack of transparency respecting Chinese companies may also reduce the Fund’s ability to conduct diligence respecting those companies’ accounting and governance standards, which may in turn reduce the Fund’s ability to detect fraudulent practices that may adversely affect the companies’ stock prices.

Small and Mid-Cap Company Risk – Investments in small-capitalization companies and mid-capitalization companies may involve additional risks, which may be relatively higher with smaller companies. These additional risks may result from limited product lines, more limited access to markets and financial resources, greater vulnerability to competition and changes in markets, lack of management depth, increased volatility in share price, and possible difficulties in valuing or selling these investments.

Credit Risk – The inability of an issuer to pay principal and interest on its debt obligations when due, or the downgrading of an issuer’s debt obligations by ratings agencies, may adversely affect the market’s perceptions of the issuer’s financial strength and may therefore result in declines in the issuer’s stock price.

Liquidity Risk – Due to a lack of demand in the marketplace or other factors, the Fund may not be able to sell some or all of its investments promptly, or may only be able to sell investments at less than desired prices.

Cybersecurity and Operational Risk – Operational failures, cyber-attacks or other disruptions that affect the Fund’s service providers, the Fund’s counterparties, other market participants or the issuers of securities held by the Fund may adversely affect the Fund and its shareholders, including by causing losses for the Fund or impairing Fund operations.

Additional information about Fund investments, investment strategies, and risks of investing in the Fund appears beginning on page 61 of the Prospectus.
Risk Lose Money [Text] rr_RiskLoseMoney Accordingly, the loss of money is a risk of investing in the Fund.
RIsk Not Insured [Text] rr_RiskNotInsured An investment in the Fund is not a deposit in any bank and is not insured or guaranteed by the Federal Deposit Insurance Corporation or any other governmental agency.
Bar Chart and Performance Table [Heading] rr_BarChartAndPerformanceTableHeading Past Performance of the Fund
Performance Narrative [Text Block] rr_PerformanceNarrativeTextBlock

The following information provides some indication of the risks of investing in International Value Fund by showing how the Fund’s investment results vary from year to year. The bar chart shows how the annual total returns for Class R3 shares vary in each full year shown. The average annual total return figures compare Class R3, Class R4, Class R5 and Class R6 share performance to the MSCI ACWI ex USA Net Total Return USD Index (primary index) and the MSCI EAFE Net Total Return USD Index (secondary index), each of which is a broad measure of market performance. Past performance (before and after taxes) is not necessarily an indication of how the Fund will perform in the future. The performance information shown below is as of the calendar year ended December 31, 2021. Updated performance information may be obtained on the Thornburg website at www.thornburg.com or by calling 1-800-847-0200.

Effective as of February 1, 2022, the MSCI ACWI ex USA Net Total Return USD Index replaced the MSCI EAFE Net Total Return USD Index as the Fund’s primary index. Thornburg believes that the MSCI ACWI ex USA Net Total Return USD Index more closely aligns with the Fund’s investment strategies than the MSCI EAFE Net Total Return USD Index.
Performance Information Illustrates Variability of Returns [Text] rr_PerformanceInformationIllustratesVariabilityOfReturns The following information provides some indication of the risks of investing in International Value Fund by showing how the Fund’s investment results vary from year to year.
Performance Availability Phone [Text] rr_PerformanceAvailabilityPhone 1-800-847-0200
Performance Availability Website Address [Text] rr_PerformanceAvailabilityWebSiteAddress www.thornburg.com
Performance Past Does Not Indicate Future [Text] rr_PerformancePastDoesNotIndicateFuture Past performance (before and after taxes) is not necessarily an indication of how the Fund will perform in the future.
Bar Chart [Heading] rr_BarChartHeading Annual Total Returns – Class R3 Shares
Bar Chart Closing [Text Block] rr_BarChartClosingTextBlock

Total
Returns

Quarter
ended

Highest Quarterly Results

18.40%

6/30/2020

Lowest Quarterly Results

(20.95)%

9/30/2011
Performance Table Heading rr_PerformanceTableHeading Average Annual Total Returns (periods ended 12-31-21)
Performance Table Market Index Changed rr_PerformanceTableMarketIndexChanged Effective as of February 1, 2022, the MSCI ACWI ex USA Net Total Return USD Index replaced the MSCI EAFE Net Total Return USD Index as the Fund’s primary index.
Performance Table Uses Highest Federal Rate rr_PerformanceTableUsesHighestFederalRate After-tax returns are calculated using the highest historical individual federal marginal income tax rates, and do not reflect state or local income taxes.
Performance Table Not Relevant to Tax Deferred rr_PerformanceTableNotRelevantToTaxDeferred Actual after-tax returns depend on an investor’s own tax situation and may differ from the returns shown, and after-tax returns shown are not relevant to investors who hold their Fund shares through tax-deferred arrangements, such as 401(k) plans or individual retirement accounts.
Performance Table One Class of after Tax Shown [Text] rr_PerformanceTableOneClassOfAfterTaxShown The after-tax returns shown relate only to Class R3 shares, and after-tax returns for other share classes will vary.
Performance Table Closing [Text Block] rr_PerformanceTableClosingTextBlock

After-tax returns are calculated using the highest historical individual federal marginal income tax rates, and do not reflect state or local income taxes. Actual after-tax returns depend on an investor’s own tax situation and may differ from the returns shown, and after-tax returns shown are not relevant to investors who hold their Fund shares through tax-deferred arrangements, such as 401(k) plans or individual retirement accounts. The after-tax returns shown relate only to Class R3 shares, and after-tax returns for other share classes will vary.
Retirement | Thornburg International Equity Fund | Thornburg International Equity Fund - Class R3  
Prospectus [Line Items] rr_ProspectusLineItems  
Trading Symbol dei_TradingSymbol TGVRX
Maximum Sales Charge Imposed on Purchases (as a percentage of Offering Price) rr_MaximumSalesChargeImposedOnPurchasesOverOfferingPrice none
Maximum Deferred Sales Charge (as a percentage) rr_MaximumDeferredSalesChargeOverOther none
Management Fees (as a percentage of Assets) rr_ManagementFeesOverAssets 0.74%
Distribution and Service (12b-1) Fees rr_DistributionAndService12b1FeesOverAssets 0.50%
Other Expenses (as a percentage of Assets): rr_OtherExpensesOverAssets 0.37% [61]
Expenses (as a percentage of Assets) rr_ExpensesOverAssets 1.61%
Fee Waiver or Reimbursement rr_FeeWaiverOrReimbursementOverAssets (0.25%) [62]
Net Expenses (as a percentage of Assets) rr_NetExpensesOverAssets 1.36%
Expense Example, with Redemption, 1 Year rr_ExpenseExampleYear01 $ 138
Expense Example, with Redemption, 3 Years rr_ExpenseExampleYear03 484
Expense Example, with Redemption, 5 Years rr_ExpenseExampleYear05 853
Expense Example, with Redemption, 10 Years rr_ExpenseExampleYear10 $ 1,890
Annual Return 2012 rr_AnnualReturn2012 15.18%
Annual Return 2013 rr_AnnualReturn2013 15.09%
Annual Return 2014 rr_AnnualReturn2014 (6.06%)
Annual Return 2015 rr_AnnualReturn2015 6.07%
Annual Return 2016 rr_AnnualReturn2016 (2.88%)
Annual Return 2017 rr_AnnualReturn2017 24.78%
Annual Return 2018 rr_AnnualReturn2018 (20.22%)
Annual Return 2019 rr_AnnualReturn2019 28.39%
Annual Return 2020 rr_AnnualReturn2020 22.12%
Annual Return 2021 rr_AnnualReturn2021 7.10%
Highest Quarterly Return, Label rr_HighestQuarterlyReturnLabel Highest Quarterly Results
Highest Quarterly Return, Date rr_BarChartHighestQuarterlyReturnDate Jun. 30, 2020
Highest Quarterly Return rr_BarChartHighestQuarterlyReturn 18.40%
Lowest Quarterly Return, Label rr_LowestQuarterlyReturnLabel Lowest Quarterly Results
Lowest Quarterly Return, Date rr_BarChartLowestQuarterlyReturnDate Sep. 30, 2011
Lowest Quarterly Return rr_BarChartLowestQuarterlyReturn (20.95%)
1 Year rr_AverageAnnualReturnYear01 7.10%
5 Years rr_AverageAnnualReturnYear05 10.83%
10 Years rr_AverageAnnualReturnYear10 7.93%
Retirement | Thornburg International Equity Fund | Thornburg International Equity Fund - Class R3 | After Taxes on Distributions  
Prospectus [Line Items] rr_ProspectusLineItems  
1 Year rr_AverageAnnualReturnYear01 2.98%
5 Years rr_AverageAnnualReturnYear05 8.40%
10 Years rr_AverageAnnualReturnYear10 5.94%
Retirement | Thornburg International Equity Fund | Thornburg International Equity Fund - Class R3 | After Taxes on Distributions and Sales  
Prospectus [Line Items] rr_ProspectusLineItems  
1 Year rr_AverageAnnualReturnYear01 5.55%
5 Years rr_AverageAnnualReturnYear05 7.90%
10 Years rr_AverageAnnualReturnYear10 5.80%
Retirement | Thornburg International Equity Fund | Thornburg International Equity Fund - Class R3 | MSCI AC World ex-U.S. Index (reflects no deduction for fees, expenses, or U.S. taxes)  
Prospectus [Line Items] rr_ProspectusLineItems  
1 Year rr_AverageAnnualReturnYear01 7.82%
5 Years rr_AverageAnnualReturnYear05 9.61%
10 Years rr_AverageAnnualReturnYear10 7.28%
Retirement | Thornburg International Equity Fund | Thornburg International Equity Fund - Class R3 | MSCI EAFE Index (reflects no deduction for fees, expenses, or U.S. taxes)  
Prospectus [Line Items] rr_ProspectusLineItems  
1 Year rr_AverageAnnualReturnYear01 11.26%
5 Years rr_AverageAnnualReturnYear05 9.55%
10 Years rr_AverageAnnualReturnYear10 8.03%
Retirement | Thornburg International Equity Fund | Thornburg International Equity Fund - Class R4  
Prospectus [Line Items] rr_ProspectusLineItems  
Trading Symbol dei_TradingSymbol THVRX
Maximum Sales Charge Imposed on Purchases (as a percentage of Offering Price) rr_MaximumSalesChargeImposedOnPurchasesOverOfferingPrice none
Maximum Deferred Sales Charge (as a percentage) rr_MaximumDeferredSalesChargeOverOther none
Management Fees (as a percentage of Assets) rr_ManagementFeesOverAssets 0.74%
Distribution and Service (12b-1) Fees rr_DistributionAndService12b1FeesOverAssets 0.25%
Other Expenses (as a percentage of Assets): rr_OtherExpensesOverAssets 0.41% [61]
Expenses (as a percentage of Assets) rr_ExpensesOverAssets 1.40%
Fee Waiver or Reimbursement rr_FeeWaiverOrReimbursementOverAssets (0.24%) [62]
Net Expenses (as a percentage of Assets) rr_NetExpensesOverAssets 1.16%
Expense Example, with Redemption, 1 Year rr_ExpenseExampleYear01 $ 118
Expense Example, with Redemption, 3 Years rr_ExpenseExampleYear03 420
Expense Example, with Redemption, 5 Years rr_ExpenseExampleYear05 743
Expense Example, with Redemption, 10 Years rr_ExpenseExampleYear10 $ 1,659
1 Year rr_AverageAnnualReturnYear01 7.30%
5 Years rr_AverageAnnualReturnYear05 11.05%
10 Years rr_AverageAnnualReturnYear10 8.14%
Retirement | Thornburg International Equity Fund | Thornburg International Equity Fund - Class R4 | MSCI AC World ex-U.S. Index (reflects no deduction for fees, expenses, or U.S. taxes)  
Prospectus [Line Items] rr_ProspectusLineItems  
1 Year rr_AverageAnnualReturnYear01 7.82%
5 Years rr_AverageAnnualReturnYear05 9.61%
10 Years rr_AverageAnnualReturnYear10 7.28%
Retirement | Thornburg International Equity Fund | Thornburg International Equity Fund - Class R4 | MSCI EAFE Index (reflects no deduction for fees, expenses, or U.S. taxes)  
Prospectus [Line Items] rr_ProspectusLineItems  
1 Year rr_AverageAnnualReturnYear01 11.26%
5 Years rr_AverageAnnualReturnYear05 9.55%
10 Years rr_AverageAnnualReturnYear10 8.03%
Retirement | Thornburg International Equity Fund | Thornburg International Equity Fund - Class R5  
Prospectus [Line Items] rr_ProspectusLineItems  
Trading Symbol dei_TradingSymbol TIVRX
Maximum Sales Charge Imposed on Purchases (as a percentage of Offering Price) rr_MaximumSalesChargeImposedOnPurchasesOverOfferingPrice none
Maximum Deferred Sales Charge (as a percentage) rr_MaximumDeferredSalesChargeOverOther none
Management Fees (as a percentage of Assets) rr_ManagementFeesOverAssets 0.74%
Distribution and Service (12b-1) Fees rr_DistributionAndService12b1FeesOverAssets none
Other Expenses (as a percentage of Assets): rr_OtherExpensesOverAssets 0.42% [61]
Expenses (as a percentage of Assets) rr_ExpensesOverAssets 1.16%
Fee Waiver or Reimbursement rr_FeeWaiverOrReimbursementOverAssets (0.26%) [62]
Net Expenses (as a percentage of Assets) rr_NetExpensesOverAssets 0.90%
Expense Example, with Redemption, 1 Year rr_ExpenseExampleYear01 $ 92
Expense Example, with Redemption, 3 Years rr_ExpenseExampleYear03 343
Expense Example, with Redemption, 5 Years rr_ExpenseExampleYear05 613
Expense Example, with Redemption, 10 Years rr_ExpenseExampleYear10 $ 1,386
1 Year rr_AverageAnnualReturnYear01 7.57%
5 Years rr_AverageAnnualReturnYear05 11.34%
10 Years rr_AverageAnnualReturnYear10 8.43%
Retirement | Thornburg International Equity Fund | Thornburg International Equity Fund - Class R5 | MSCI AC World ex-U.S. Index (reflects no deduction for fees, expenses, or U.S. taxes)  
Prospectus [Line Items] rr_ProspectusLineItems  
1 Year rr_AverageAnnualReturnYear01 7.82%
5 Years rr_AverageAnnualReturnYear05 9.61%
10 Years rr_AverageAnnualReturnYear10 7.28%
Retirement | Thornburg International Equity Fund | Thornburg International Equity Fund - Class R5 | MSCI EAFE Index (reflects no deduction for fees, expenses, or U.S. taxes)  
Prospectus [Line Items] rr_ProspectusLineItems  
1 Year rr_AverageAnnualReturnYear01 11.26%
5 Years rr_AverageAnnualReturnYear05 9.55%
10 Years rr_AverageAnnualReturnYear10 8.03%
Retirement | Thornburg International Equity Fund | Thornburg International Equity Fund - Class R6  
Prospectus [Line Items] rr_ProspectusLineItems  
Trading Symbol dei_TradingSymbol TGIRX
Maximum Sales Charge Imposed on Purchases (as a percentage of Offering Price) rr_MaximumSalesChargeImposedOnPurchasesOverOfferingPrice none
Maximum Deferred Sales Charge (as a percentage) rr_MaximumDeferredSalesChargeOverOther none
Management Fees (as a percentage of Assets) rr_ManagementFeesOverAssets 0.74%
Distribution and Service (12b-1) Fees rr_DistributionAndService12b1FeesOverAssets none
Other Expenses (as a percentage of Assets): rr_OtherExpensesOverAssets 0.14% [61]
Expenses (as a percentage of Assets) rr_ExpensesOverAssets 0.88%
Fee Waiver or Reimbursement rr_FeeWaiverOrReimbursementOverAssets (0.18%) [62]
Net Expenses (as a percentage of Assets) rr_NetExpensesOverAssets 0.70%
Expense Example, with Redemption, 1 Year rr_ExpenseExampleYear01 $ 72
Expense Example, with Redemption, 3 Years rr_ExpenseExampleYear03 263
Expense Example, with Redemption, 5 Years rr_ExpenseExampleYear05 470
Expense Example, with Redemption, 10 Years rr_ExpenseExampleYear10 $ 1,068
1 Year rr_AverageAnnualReturnYear01 7.77%
5 Years rr_AverageAnnualReturnYear05 11.56%
Since Inception rr_AverageAnnualReturnSinceInception 7.82%
Inception Date rr_AverageAnnualReturnInceptionDate May 01, 2012
Retirement | Thornburg International Equity Fund | Thornburg International Equity Fund - Class R6 | MSCI AC World ex-U.S. Index (reflects no deduction for fees, expenses, or U.S. taxes)  
Prospectus [Line Items] rr_ProspectusLineItems  
1 Year rr_AverageAnnualReturnYear01 7.82%
5 Years rr_AverageAnnualReturnYear05 9.61%
Since Inception rr_AverageAnnualReturnSinceInception 6.55%
Retirement | Thornburg International Equity Fund | Thornburg International Equity Fund - Class R6 | MSCI EAFE Index (reflects no deduction for fees, expenses, or U.S. taxes)  
Prospectus [Line Items] rr_ProspectusLineItems  
1 Year rr_AverageAnnualReturnYear01 11.26%
5 Years rr_AverageAnnualReturnYear05 9.55%
Since Inception rr_AverageAnnualReturnSinceInception 7.41%
Retirement | Thornburg International Growth Fund  
Prospectus [Line Items] rr_ProspectusLineItems  
Risk/Return [Heading] rr_RiskReturnHeading International Growth Fund
Objective [Heading] rr_ObjectiveHeading Investment Goal
Objective, Primary [Text Block] rr_ObjectivePrimaryTextBlock

The Fund seeks long-term growth of capital by investing in equity securities selected for their growth potential.

Expense [Heading] rr_ExpenseHeading Fees and Expenses of the Fund
Expense Narrative [Text Block] rr_ExpenseNarrativeTextBlock

This table describes the fees and expenses that you may pay if you buy and hold shares of the Fund.
Shareholder Fees Caption [Text] rr_ShareholderFeesCaption Shareholder Fees (fees paid directly from your investment)
Operating Expenses Caption [Text] rr_OperatingExpensesCaption Annual Fund Operating Expenses (expenses that you pay each year as a percentage of the value of your investment)
Fee Waiver or Reimbursement over Assets, Date of Termination rr_FeeWaiverOrReimbursementOverAssetsDateOfTermination February 1, 2023
Portfolio Turnover [Heading] rr_PortfolioTurnoverHeading Portfolio Turnover.
Portfolio Turnover [Text Block] rr_PortfolioTurnoverTextBlock

The Fund pays transaction costs, such as commissions, when it buys and sells securities (or “turns over”) its portfolio. A higher portfolio turnover rate may indicate higher transaction costs and may result in higher taxes when Fund shares are held in a taxable account. These costs, which are not reflected in Annual Fund Operating Expenses or in the Example, affect the Fund’s performance. During the most recent fiscal year, the Fund’s portfolio turnover rate was 34.41% of the average value of its portfolio.
Portfolio Turnover, Rate rr_PortfolioTurnoverRate 34.41%
Expense Example [Heading] rr_ExpenseExampleHeading Example.
Expense Example Narrative [Text Block] rr_ExpenseExampleNarrativeTextBlock

This Example is intended to help you compare the cost of investing in the Fund with the cost of investing in other mutual funds.

The Example assumes that you invest $10,000 in the Fund for the time periods indicated and then redeem all of your shares at the end of those periods. The Example also assumes that your investment has a 5% return each year, dividends and distributions are reinvested, and that the Fund’s operating expenses remain the same. Although your actual costs may be higher or lower, based on these assumptions (and giving effect to fee waivers and expense reimbursements in the first year), your costs would be:
Strategy [Heading] rr_StrategyHeading Principal Investment Strategies
Strategy Narrative [Text Block] rr_StrategyNarrativeTextBlock

The Fund expects to invest primarily in equity securities from issuers around the world (primarily common stocks) selected for their growth potential and, under normal market conditions, invests at least 75% of its assets in foreign securities or depositary receipts of foreign securities. However, the Fund may own a variety of securities, including domestic equity securities. The Fund may invest in developing countries.

The Fund’s investment advisor, Thornburg Investment Management, Inc. (“Thornburg”) intends to invest in companies that it believes will have growing revenues and earnings. The Fund can invest in companies of any size, from larger, well-established companies to smaller, emerging growth companies.

Thornburg primarily uses individual issuer and industry analysis to make investment decisions. Among the specific factors considered by Thornburg in identifying securities for inclusion in the Fund are:

•earnings growth potential

•business model

•industry growth potential

•industry leadership

•asset appreciation potential

•potential size of business

•price/earnings ratio

•price/revenue ratio

•PE/growth rate ratio

•price/cash flow ratio

•enterprise value/EBITDA (earnings before interest, taxes, depreciation and amortization) ratio

•management strength

•debt/capital ratio

The Fund typically makes equity investments in the following three types of companies:

Growth Industry Leaders: Companies in this category often have leadership positions in growing markets. In some cases these companies may have dominant market share. These companies tend to be larger and more established.

Consistent Growers: Companies in this category generally exhibit steady earnings or revenue growth, or both. These companies may have subscription or other recurring revenue profiles. Given their business models, these companies may outperform in weak markets.

Emerging Growth Companies: Companies often addressing a new market or carving out a niche in an existing market. Companies in this category may experience rapid growth, and tend to be smaller, earlier stage companies. These companies may exhibit high volatility.

Inclusion of any investment in any of the three described categories represents the opinion of the advisor concerning the characteristics and prospects of the investment. There is no assurance that any company selected for investment will, once categorized in one of the three described investment categories, continue to have the positive characteristics or fulfill the expectations that the advisor had for the company when it was selected for investment, and any such company may not grow or may decline in earnings and size.

In conjunction with individual issuer analysis, Thornburg may identify and invest at times with a greater emphasis in industries or economic sectors it expects to experience growth. This approach may at times produce a greater emphasis on investment in certain industries or economic sectors, such as technology, financial services, healthcare or biotechnology. The Fund does not have a strategy to invest in particular industry or economic sectors, and its exposures to particular industries or economic sectors are expected to vary over time. Investment decisions are also based on domestic and international economic developments, outlooks for securities markets, interest rates and inflation, and the supply and demand for securities.

The Fund may sell an investment if Thornburg has identified a better investment opportunity, in response to changes in the conditions or business of the investment’s issuer or changes in overall market conditions, if Thornburg has a target price for the investment and that target price has been achieved, or if, in Thornburg’s opinion, the investment no longer serves to achieve the Fund’s investment goals.
Risk [Heading] rr_RiskHeading Principal Investment Risks
Risk Narrative [Text Block] rr_RiskNarrativeTextBlock

An investment in the Fund is not a deposit in any bank and is not insured or guaranteed by the Federal Deposit Insurance Corporation or any other governmental agency. Accordingly, the loss of money is a risk of investing in the Fund. The value of the Fund’s shares varies from day to day and over time, and when you sell your shares they may be worth less than what you paid for them. The following is a summary of the principal risks of investing in the Fund.

Management Risk – The Fund is an actively managed portfolio, and the value of the Fund may be reduced if Thornburg pursues unsuccessful investments or fails to correctly identify risks affecting the broad economy or specific issuers in which the Fund invests.

Market and Economic Risk – The value of the Fund’s investments may decline and its share value may be reduced due to changes in general economic and market conditions. The value of a security may change in response to developments affecting entire economies, markets or industries, including changes in interest rates, political and legal developments, and general market volatility.

Equity Risk – The value of the Fund’s equity investments may fluctuate significantly over time in response to factors affecting individual issuers, particular industries, or the market as a whole. Additionally, common stock ranks below preferred stock and debt securities in claims for dividends and for assets of a company in a liquidation or bankruptcy.

Risks Affecting Specific Issuers – The value of a security may decline in response to developments affecting the specific issuer of the security, even if the overall industry or economy is unaffected. These developments may include a variety of factors, including but not limited to management issues or other corporate disruption, a decline in revenues or profitability, an increase in costs, or an adverse effect on the issuer’s competitive position.

Foreign Investment Risk – Investments in securities of foreign issuers may involve risks including adverse fluctuations in currency exchange rates, political instability, confiscations, taxes or restrictions on currency exchange, difficulty in selling foreign investments, and reduced legal protection.

Developing Country Risk – The risks which may affect investments in foreign issuers (see “Foreign Investment Risk,” above) may be more pronounced for investments in developing countries because the economies of those countries are usually less diversified, communications, transportation and economic infrastructures are less developed, and developing countries ordinarily have less established legal, political, business and social frameworks. At times the prices of equity securities of a developing country issuer may be extremely volatile. An issuer domiciled in a developed country may be similarly affected by these developing country risks to the extent that the issuer conducts its business in developing countries.

Foreign Currency Risk – Fluctuations in currency exchange rates can adversely affect the value of the Fund’s foreign investments. Such fluctuations may occur for a number of reasons, including market and economic conditions, or a government’s decision to devalue its currency or impose currency controls.

Risks Affecting Specific Countries or Regions – If a significant portion of the Fund’s assets is invested in issuers that are economically exposed to one country or region, the Fund’s share value may be more susceptible to the conditions and developments in that country or region, and potentially more volatile than the share value of a more geographically diversified fund. A specific country or region could also be adversely affected by conditions or developments arising in other countries. For example, the U.S. government could take actions to prohibit or restrict individuals or companies within the U.S. from purchasing or holding the shares of issuers in another country, which may limit the Fund’s ability to invest in that country or cause the Fund to have to sell investments in that country at less than desired prices. The nature and degree of the risks affecting a given country or region, and the extent of the Fund’s exposure to any such country or region, is expected to vary over time.

Small and Mid-Cap Company Risk – Investments in small-capitalization companies and mid-capitalization companies, including smaller, earlier stage companies, may involve additional risks. These risks may be relatively higher with smaller companies. These additional risks may result from limited product lines, more limited access to markets and financial resources, greater vulnerability to competition and changes in markets, lack of management depth, increased volatility in share price, and possible difficulties in valuing or selling these investments.

Credit Risk – The inability of an issuer to pay principal and interest on its debt obligations when due, or the downgrading of an issuer’s debt obligations by ratings agencies, may adversely affect the market’s perceptions of the issuer’s financial strength and may therefore result in declines in the issuer’s stock price.

Liquidity Risk – Due to a lack of demand in the marketplace or other factors, the Fund may not be able to sell some or all of its investments promptly, or may only be able to sell investments at less than desired prices. This risk may be more pronounced for the Fund’s investments in developing countries.

Cybersecurity and Operational Risk – Operational failures, cyber-attacks or other disruptions that affect the Fund’s service providers, the Fund’s counterparties, other market participants or the issuers of securities held by the Fund may adversely affect the Fund and its shareholders, including by causing losses for the Fund or impairing Fund operations.

Additional information about Fund investments, investment strategies, and risks of investing in the Fund appears beginning on page 61 of the Prospectus.
Risk Lose Money [Text] rr_RiskLoseMoney Accordingly, the loss of money is a risk of investing in the Fund.
RIsk Not Insured [Text] rr_RiskNotInsured An investment in the Fund is not a deposit in any bank and is not insured or guaranteed by the Federal Deposit Insurance Corporation or any other governmental agency.
Bar Chart and Performance Table [Heading] rr_BarChartAndPerformanceTableHeading Past Performance of the Fund
Performance Narrative [Text Block] rr_PerformanceNarrativeTextBlock

The following information provides some indication of the risks of investing in International Growth Fund by showing how the Fund’s investment results vary from year to year. The bar chart shows how the annual total returns for Class R3 shares vary in each full year shown. The average annual total return figures compare Class R3, Class R4, Class R5 and Class R6 share performance to the MSCI ACWI ex USA Growth Net Total Return USD Index, a market capitalization weighted index which includes growth companies in developed and emerging markets throughout the world, excluding the United States. Past performance (before and after taxes) is not necessarily an indication of how the Fund will perform in the future. The performance information shown below is as of the calendar year ended December 31, 2021. Updated performance information may be obtained on the Thornburg website at www.thornburg.com or by calling 1-800-847-0200.
Performance Information Illustrates Variability of Returns [Text] rr_PerformanceInformationIllustratesVariabilityOfReturns The following information provides some indication of the risks of investing in International Growth Fund by showing how the Fund’s investment results vary from year to year.
Performance Availability Phone [Text] rr_PerformanceAvailabilityPhone 1-800-847-0200
Performance Availability Website Address [Text] rr_PerformanceAvailabilityWebSiteAddress www.thornburg.com
Performance Past Does Not Indicate Future [Text] rr_PerformancePastDoesNotIndicateFuture Past performance (before and after taxes) is not necessarily an indication of how the Fund will perform in the future.
Bar Chart [Heading] rr_BarChartHeading Annual Total Returns – Class R3 Shares
Bar Chart Closing [Text Block] rr_BarChartClosingTextBlock

Total
Returns

Quarter
ended

Highest Quarterly Results

25.89%

6/30/2020

Lowest Quarterly Results

(17.77)%

12/31/2018
Performance Table Heading rr_PerformanceTableHeading Average Annual Total Returns (periods ended 12-31-21)
Performance Table Uses Highest Federal Rate rr_PerformanceTableUsesHighestFederalRate After-tax returns are calculated using the highest historical individual federal marginal income tax rates, and do not reflect state or local income taxes.
Performance Table Not Relevant to Tax Deferred rr_PerformanceTableNotRelevantToTaxDeferred Actual after-tax returns depend on an investor’s own tax situation and may differ from the returns shown, and after-tax returns shown are not relevant to investors who hold their Fund shares through tax-deferred arrangements, such as 401(k) plans or individual retirement accounts.
Performance Table One Class of after Tax Shown [Text] rr_PerformanceTableOneClassOfAfterTaxShown The after-tax returns shown relate only to Class R3 shares, and after-tax returns for other share classes will vary.
Performance Table Closing [Text Block] rr_PerformanceTableClosingTextBlock

After-tax returns are calculated using the highest historical individual federal marginal income tax rates, and do not reflect state or local income taxes. Actual after-tax returns depend on an investor’s own tax situation and may differ from the returns shown, and after-tax returns shown are not relevant to investors who hold their Fund shares through tax-deferred arrangements, such as 401(k) plans or individual retirement accounts. The after-tax returns shown relate only to Class R3 shares, and after-tax returns for other share classes will vary.
Retirement | Thornburg International Growth Fund | Thornburg International Growth Fund - Class R3  
Prospectus [Line Items] rr_ProspectusLineItems  
Trading Symbol dei_TradingSymbol TIGVX
Maximum Sales Charge Imposed on Purchases (as a percentage of Offering Price) rr_MaximumSalesChargeImposedOnPurchasesOverOfferingPrice none
Maximum Deferred Sales Charge (as a percentage) rr_MaximumDeferredSalesChargeOverOther none
Management Fees (as a percentage of Assets) rr_ManagementFeesOverAssets 0.80%
Distribution and Service (12b-1) Fees rr_DistributionAndService12b1FeesOverAssets 0.50%
Other Expenses (as a percentage of Assets): rr_OtherExpensesOverAssets 0.58% [63]
Expenses (as a percentage of Assets) rr_ExpensesOverAssets 1.88%
Fee Waiver or Reimbursement rr_FeeWaiverOrReimbursementOverAssets (0.38%) [64]
Net Expenses (as a percentage of Assets) rr_NetExpensesOverAssets 1.50%
Expense Example, with Redemption, 1 Year rr_ExpenseExampleYear01 $ 153
Expense Example, with Redemption, 3 Years rr_ExpenseExampleYear03 554
Expense Example, with Redemption, 5 Years rr_ExpenseExampleYear05 981
Expense Example, with Redemption, 10 Years rr_ExpenseExampleYear10 $ 2,170
Annual Return 2012 rr_AnnualReturn2012 21.88%
Annual Return 2013 rr_AnnualReturn2013 36.21%
Annual Return 2014 rr_AnnualReturn2014 (12.56%)
Annual Return 2015 rr_AnnualReturn2015 6.25%
Annual Return 2016 rr_AnnualReturn2016 (5.16%)
Annual Return 2017 rr_AnnualReturn2017 34.22%
Annual Return 2018 rr_AnnualReturn2018 (17.18%)
Annual Return 2019 rr_AnnualReturn2019 25.66%
Annual Return 2020 rr_AnnualReturn2020 33.64%
Annual Return 2021 rr_AnnualReturn2021 (4.69%)
Highest Quarterly Return, Label rr_HighestQuarterlyReturnLabel Highest Quarterly Results
Highest Quarterly Return, Date rr_BarChartHighestQuarterlyReturnDate Jun. 30, 2020
Highest Quarterly Return rr_BarChartHighestQuarterlyReturn 25.89%
Lowest Quarterly Return, Label rr_LowestQuarterlyReturnLabel Lowest Quarterly Results
Lowest Quarterly Return, Date rr_BarChartLowestQuarterlyReturnDate Dec. 31, 2018
Lowest Quarterly Return rr_BarChartLowestQuarterlyReturn (17.77%)
1 Year rr_AverageAnnualReturnYear01 (4.69%)
5 Years rr_AverageAnnualReturnYear05 12.21%
10 Years rr_AverageAnnualReturnYear10 10.04%
Retirement | Thornburg International Growth Fund | Thornburg International Growth Fund - Class R3 | After Taxes on Distributions  
Prospectus [Line Items] rr_ProspectusLineItems  
1 Year rr_AverageAnnualReturnYear01 (6.19%)
5 Years rr_AverageAnnualReturnYear05 11.34%
10 Years rr_AverageAnnualReturnYear10 9.34%
Retirement | Thornburg International Growth Fund | Thornburg International Growth Fund - Class R3 | After Taxes on Distributions and Sales  
Prospectus [Line Items] rr_ProspectusLineItems  
1 Year rr_AverageAnnualReturnYear01 (1.67%)
5 Years rr_AverageAnnualReturnYear05 9.63%
10 Years rr_AverageAnnualReturnYear10 8.10%
Retirement | Thornburg International Growth Fund | Thornburg International Growth Fund - Class R3 | MSCI AC World ex-U.S. Growth Index (reflects no deduction for fees, expenses, or U.S. taxes)  
Prospectus [Line Items] rr_ProspectusLineItems  
1 Year rr_AverageAnnualReturnYear01 5.09%
5 Years rr_AverageAnnualReturnYear05 13.06%
10 Years rr_AverageAnnualReturnYear10 9.13%
Retirement | Thornburg International Growth Fund | Thornburg International Growth Fund - Class R4  
Prospectus [Line Items] rr_ProspectusLineItems  
Trading Symbol dei_TradingSymbol TINVX
Maximum Sales Charge Imposed on Purchases (as a percentage of Offering Price) rr_MaximumSalesChargeImposedOnPurchasesOverOfferingPrice none
Maximum Deferred Sales Charge (as a percentage) rr_MaximumDeferredSalesChargeOverOther none
Management Fees (as a percentage of Assets) rr_ManagementFeesOverAssets 0.80%
Distribution and Service (12b-1) Fees rr_DistributionAndService12b1FeesOverAssets 0.25%
Other Expenses (as a percentage of Assets): rr_OtherExpensesOverAssets 0.57% [63]
Expenses (as a percentage of Assets) rr_ExpensesOverAssets 1.62%
Fee Waiver or Reimbursement rr_FeeWaiverOrReimbursementOverAssets (0.22%) [64]
Net Expenses (as a percentage of Assets) rr_NetExpensesOverAssets 1.40%
Expense Example, with Redemption, 1 Year rr_ExpenseExampleYear01 $ 143
Expense Example, with Redemption, 3 Years rr_ExpenseExampleYear03 490
Expense Example, with Redemption, 5 Years rr_ExpenseExampleYear05 861
Expense Example, with Redemption, 10 Years rr_ExpenseExampleYear10 $ 1,903
1 Year rr_AverageAnnualReturnYear01 (4.56%)
5 Years rr_AverageAnnualReturnYear05 12.35%
10 Years rr_AverageAnnualReturnYear10 10.15%
Retirement | Thornburg International Growth Fund | Thornburg International Growth Fund - Class R4 | MSCI AC World ex-U.S. Growth Index (reflects no deduction for fees, expenses, or U.S. taxes)  
Prospectus [Line Items] rr_ProspectusLineItems  
1 Year rr_AverageAnnualReturnYear01 5.09%
5 Years rr_AverageAnnualReturnYear05 13.06%
10 Years rr_AverageAnnualReturnYear10 9.13%
Retirement | Thornburg International Growth Fund | Thornburg International Growth Fund - Class R5  
Prospectus [Line Items] rr_ProspectusLineItems  
Trading Symbol dei_TradingSymbol TINFX
Maximum Sales Charge Imposed on Purchases (as a percentage of Offering Price) rr_MaximumSalesChargeImposedOnPurchasesOverOfferingPrice none
Maximum Deferred Sales Charge (as a percentage) rr_MaximumDeferredSalesChargeOverOther none
Management Fees (as a percentage of Assets) rr_ManagementFeesOverAssets 0.80%
Distribution and Service (12b-1) Fees rr_DistributionAndService12b1FeesOverAssets none
Other Expenses (as a percentage of Assets): rr_OtherExpensesOverAssets 0.46% [63]
Expenses (as a percentage of Assets) rr_ExpensesOverAssets 1.26%
Fee Waiver or Reimbursement rr_FeeWaiverOrReimbursementOverAssets (0.27%) [64]
Net Expenses (as a percentage of Assets) rr_NetExpensesOverAssets 0.99%
Expense Example, with Redemption, 1 Year rr_ExpenseExampleYear01 $ 101
Expense Example, with Redemption, 3 Years rr_ExpenseExampleYear03 373
Expense Example, with Redemption, 5 Years rr_ExpenseExampleYear05 666
Expense Example, with Redemption, 10 Years rr_ExpenseExampleYear10 $ 1,499
1 Year rr_AverageAnnualReturnYear01 (4.22%)
5 Years rr_AverageAnnualReturnYear05 12.79%
10 Years rr_AverageAnnualReturnYear10 10.59%
Retirement | Thornburg International Growth Fund | Thornburg International Growth Fund - Class R5 | MSCI AC World ex-U.S. Growth Index (reflects no deduction for fees, expenses, or U.S. taxes)  
Prospectus [Line Items] rr_ProspectusLineItems  
1 Year rr_AverageAnnualReturnYear01 5.09%
5 Years rr_AverageAnnualReturnYear05 13.06%
10 Years rr_AverageAnnualReturnYear10 9.13%
Retirement | Thornburg International Growth Fund | Thornburg International Growth Fund - Class R6  
Prospectus [Line Items] rr_ProspectusLineItems  
Trading Symbol dei_TradingSymbol THGIX
Maximum Sales Charge Imposed on Purchases (as a percentage of Offering Price) rr_MaximumSalesChargeImposedOnPurchasesOverOfferingPrice none
Maximum Deferred Sales Charge (as a percentage) rr_MaximumDeferredSalesChargeOverOther none
Management Fees (as a percentage of Assets) rr_ManagementFeesOverAssets 0.80%
Distribution and Service (12b-1) Fees rr_DistributionAndService12b1FeesOverAssets none
Other Expenses (as a percentage of Assets): rr_OtherExpensesOverAssets 0.15% [63]
Expenses (as a percentage of Assets) rr_ExpensesOverAssets 0.95%
Fee Waiver or Reimbursement rr_FeeWaiverOrReimbursementOverAssets (0.06%) [64]
Net Expenses (as a percentage of Assets) rr_NetExpensesOverAssets 0.89%
Expense Example, with Redemption, 1 Year rr_ExpenseExampleYear01 $ 91
Expense Example, with Redemption, 3 Years rr_ExpenseExampleYear03 297
Expense Example, with Redemption, 5 Years rr_ExpenseExampleYear05 520
Expense Example, with Redemption, 10 Years rr_ExpenseExampleYear10 $ 1,161
1 Year rr_AverageAnnualReturnYear01 (4.08%)
5 Years rr_AverageAnnualReturnYear05 12.91%
Since Inception rr_AverageAnnualReturnSinceInception 8.93%
Inception Date rr_AverageAnnualReturnInceptionDate Feb. 01, 2013
Retirement | Thornburg International Growth Fund | Thornburg International Growth Fund - Class R6 | MSCI AC World ex-U.S. Growth Index (reflects no deduction for fees, expenses, or U.S. taxes)  
Prospectus [Line Items] rr_ProspectusLineItems  
1 Year rr_AverageAnnualReturnYear01 5.09%
5 Years rr_AverageAnnualReturnYear05 13.06%
Since Inception rr_AverageAnnualReturnSinceInception 7.89%
Retirement | Thornburg Developing World Fund  
Prospectus [Line Items] rr_ProspectusLineItems  
Risk/Return [Heading] rr_RiskReturnHeading Developing World Fund
Objective [Heading] rr_ObjectiveHeading Investment Goal
Objective, Primary [Text Block] rr_ObjectivePrimaryTextBlock

The Fund’s primary investment goal is long-term capital appreciation.

Expense [Heading] rr_ExpenseHeading Fees and Expenses of the Fund
Expense Narrative [Text Block] rr_ExpenseNarrativeTextBlock

This table describes the fees and expenses that you may pay if you buy and hold shares of the Fund.

Shareholder Fees Caption [Text] rr_ShareholderFeesCaption Shareholder Fees (fees paid directly from your investment)
Operating Expenses Caption [Text] rr_OperatingExpensesCaption Annual Fund Operating Expenses (expenses that you pay each year as a percentage of the value of your investment)
Fee Waiver or Reimbursement over Assets, Date of Termination rr_FeeWaiverOrReimbursementOverAssetsDateOfTermination February 1, 2023
Portfolio Turnover [Heading] rr_PortfolioTurnoverHeading Portfolio Turnover.
Portfolio Turnover [Text Block] rr_PortfolioTurnoverTextBlock

The Fund pays transaction costs, such as commissions, when it buys and sells securities (or “turns over” its portfolio). A higher portfolio turnover rate may indicate higher transaction costs and may result in higher taxes when Fund shares are held in a taxable account. These costs, which are not reflected in Annual Fund Operating Expenses or in the Example, affect the Fund’s performance. During the most recent fiscal year, the Fund’s portfolio turnover rate was 61.50% of the average value of its portfolio.
Portfolio Turnover, Rate rr_PortfolioTurnoverRate 61.50%
Expense Example [Heading] rr_ExpenseExampleHeading Example.
Expense Example Narrative [Text Block] rr_ExpenseExampleNarrativeTextBlock

This Example is intended to help you compare the cost of investing in the Fund with the cost of investing in other mutual funds.

The Example assumes that you invest $10,000 in the Fund for the time periods indicated and then redeem all of your shares at the end of those periods. The Example also assumes that your investment has a 5% return each year, dividends and distributions are reinvested, and that the Fund’s operating expenses remain the same. Although your actual costs may be higher or lower, based on these assumptions (and giving effect to fee waivers and expense reimbursements in the first year), your costs would be:
Strategy [Heading] rr_StrategyHeading Principal Investment Strategies
Strategy Narrative [Text Block] rr_StrategyNarrativeTextBlock

Under normal market conditions the Fund invests at least 80% of its assets in equity securities of developing country issuers. A developing country issuer is a company or sovereign entity that is domiciled or otherwise tied economically to one or more developing countries. The Fund may invest in issuers of any size of capitalization, including small companies.

Currently, the Fund’s investment advisor, Thornburg Investment Management, Inc. (“Thornburg”) considers developing countries to include most Central and South American, African, Asian and Eastern European nations, including, but not limited to, Argentina, Austria, Brazil, Chile, China, Colombia, Czech Republic, Egypt, Greece, Hong Kong, Hungary, India, Indonesia, Israel, South Korea, Malaysia, Mexico, Morocco, Nigeria, Pakistan, Peru, Philippines, Poland, Qatar, Romania, the Russian Federation, Slovenia, South Africa, Taiwan, Thailand, Turkey, Ukraine, the United Arab Emirates and Vietnam. Thornburg identifies what it considers to be developing countries based upon its own analysis of measures of industrialization, economic growth, population growth and other factors, and may also consider classifications by the World Bank, the International Finance Corporation, the United Nations and independent financial services firms that maintain indices of developing countries.

Thornburg considers a variety of factors to determine whether an investment is tied economically to one or more developing countries, including (i) whether or not a significant portion of the issuer’s revenues or assets are derived from or are located in developing countries, (ii) the primary trading market of the issuer’s securities, (iii) the locations of its principal offices or operations, (iv) the source of any governmental guarantees or other supports, (v) identification of the issuer’s securities within an index or other listing indicating its location in a particular developing country or region, and (vi) the extent to which the investment is otherwise exposed to the economic fortunes and risks of developing countries.

The Fund expects that under normal conditions its assets will be invested in issuers domiciled in or tied economically to a variety of different countries.

The Fund’s policy of investing at least 80% of its assets in developing country issuers may be changed by the Fund’s Trustees without a shareholder vote upon 60 days’ notice to shareholders.

Among the specific factors considered in identifying securities for inclusion in the Fund are domestic and international economic developments, outlooks for securities markets, the supply and demand for equity securities, and analysis of specific issuers. The Fund typically makes its equity investments in the following three types of issuers:

Basic Value: Companies generally operating in mature or cyclical industries and which generally exhibit more economic sensitivity and/or higher volatility in earnings and cash flow.

Consistent Earner: Companies which generally exhibit predictable growth, profitability, cash flow and/or dividends.

Emerging Franchise: Companies with the potential to grow at an above average rate because of a product or service that is establishing a new market and/or taking share from existing participants.

Inclusion of any investment in any of the three described categories represents the opinion of the advisor concerning the characteristics and prospects of the investment. There is no assurance that any company selected for investment will, once categorized in one of the three described investment categories, continue to have the positive characteristics or fulfill the expectations that the advisor had for the company when it was selected for investment, and any such company may not grow or may decline in earnings and size.

The Fund may sell an investment if Thornburg has identified a better investment opportunity, in response to changes in the conditions or business of the investment’s issuer or changes in overall market conditions, if Thornburg has a target price for the investment and that target price has been achieved, or if, in Thornburg’s opinion, the investment no longer serves to achieve the Fund’s investment goals.
Risk [Heading] rr_RiskHeading Principal Investment Risks
Risk Narrative [Text Block] rr_RiskNarrativeTextBlock

An investment in the Fund is not a deposit in any bank and is not insured or guaranteed by the Federal Deposit Insurance Corporation or any other governmental agency. Accordingly, the loss of money is a risk of investing in the Fund. The value of the Fund’s shares varies from day to day and over time, and when you sell your shares they may be worth less than what you paid for them. The following is a summary of the principal risks of investing in the Fund.

Management Risk – The Fund is an actively managed portfolio, and the value of the Fund may be reduced if Thornburg pursues unsuccessful investments or fails to correctly identify risks affecting the broad economy or specific issuers in which the Fund invests.

Market and Economic Risk – The value of the Fund’s investments may decline and its share value may be reduced due to changes in general economic and market conditions. The value of a security may change in response to developments affecting entire economies, markets or industries, including changes in interest rates, political and legal developments, and general market volatility. These risks may be more pronounced for the Fund’s investments in developing countries.

Equity Risk – The value of the Fund’s equity investments may fluctuate significantly over time in response to factors affecting individual issuers, particular industries, or the market as a whole. Additionally, common stock ranks below preferred stock and debt securities in claims for dividends and for assets of a company in a liquidation or bankruptcy.

Risks Affecting Specific Issuers – The value of an equity security may decline in response to developments affecting the specific issuer of the security or obligation, even if the overall industry or economy is unaffected. These developments may include a variety of factors, including but not limited to management issues or other corporate disruption, a decline in revenues or profitability, an increase in costs, or an adverse effect on the issuer’s competitive position.

Foreign Investment Risk – Investments in securities of foreign issuers may involve risks including adverse fluctuations in currency exchange rates, political instability, confiscations, taxes or restrictions on currency exchange, difficulty in selling foreign investments, and reduced legal protections.

Developing Country Risk – The risks which may affect investments in foreign issuers (see “Foreign Investment Risk,” above) may be more pronounced for investments in developing countries because the economies of those countries are usually less diversified, communications, transportation and economic infrastructures are less developed, and developing countries ordinarily have less established legal, political, business and social frameworks. At times the prices of equity securities of a developing country issuer may be extremely volatile. An issuer domiciled in a developed country may be similarly affected by these developing country risks to the extent that the issuer conducts its business in developing countries.

Foreign Currency Risk – Fluctuations in currency exchange rates can adversely affect the value of the Fund’s foreign investments. Such fluctuations may occur for a number of reasons, including market and economic conditions, or a government’s decision to devalue its currency or impose currency controls.

Risks Affecting Specific Countries or Regions – If a significant portion of the Fund’s assets is invested in issuers that are economically exposed to one country or region, the Fund’s share value may be more susceptible to the conditions and developments in that country or region, and potentially more volatile than the share value of a more geographically diversified fund. A specific country or region could also be adversely affected by conditions or developments arising in other countries. For example, the U.S. government could take actions to prohibit or restrict individuals or companies within the U.S. from purchasing or holding the shares of issuers in another country, which may limit the Fund’s ability to invest in that country or cause the Fund to have to sell investments in that country at less than desired prices. The nature and degree of the risks affecting a given country or region, and the extent of the Fund’s exposure to any such country or region, is expected to vary over time.

Risks Affecting Investments in China – A significant portion of the Fund’s assets may be invested in companies exposed to China. Risks affecting investments in China include a potential downturn in the Chinese economy, reduced liquidity or increased price volatility in the Chinese securities markets as a result of trading suspensions affecting Chinese issuers or other factors, the potential that the Chinese government may expand restrictions on foreign investments or the repatriation of capital, and the implementation of new tariffs or other trade barriers by China or its trading partners. A lack of transparency respecting Chinese companies may also reduce the Fund’s ability to conduct diligence respecting those companies’ accounting and governance standards, which may in turn reduce the Fund’s ability to detect fraudulent practices that may adversely affect the companies’ stock prices.

Small and Mid-Cap Company Risk – Investments in small-capitalization companies and mid-capitalization companies may involve additional risks, which may be relatively higher with smaller companies. These additional risks may result from limited product lines, more limited access to markets and financial resources, greater vulnerability to competition and changes in markets, lack of management depth, increased volatility in share price, and possible difficulties in valuing or selling these investments.

Credit Risk – The inability of an issuer to pay principal and interest on its debt obligations when due, or the downgrading of an issuer’s debt obligations by ratings agencies, may adversely affect the market’s perceptions of the issuer’s financial strength and may therefore result in declines in the issuer’s stock price.

Liquidity Risk – Due to a lack of demand in the marketplace or other factors, the Fund may not be able to sell some or all of its investments promptly, or may only be able to sell investments at less than desired prices. This risk may be more pronounced for the Fund’s investments in developing countries.

Cybersecurity and Operational Risk – Operational failures, cyber-attacks or other disruptions that affect the Fund’s service providers, the Fund’s counterparties, other market participants or the issuers of securities held by the Fund may adversely affect the Fund and its shareholders, including by causing losses for the Fund or impairing Fund operations.

Additional information about Fund investments, investment strategies and risks of investing in the Fund appears below beginning on page 61 of the Prospectus.
Risk Lose Money [Text] rr_RiskLoseMoney Accordingly, the loss of money is a risk of investing in the Fund.
RIsk Not Insured [Text] rr_RiskNotInsured An investment in the Fund is not a deposit in any bank and is not insured or guaranteed by the Federal Deposit Insurance Corporation or any other governmental agency.
Bar Chart and Performance Table [Heading] rr_BarChartAndPerformanceTableHeading Past Performance of the Fund
Performance Narrative [Text Block] rr_PerformanceNarrativeTextBlock

The following information provides some indication of the risks of investing in Developing World Fund by showing how the Fund’s investment results vary from year to year. The bar chart shows how the annual total returns for Class R5 shares have been different in each full year shown. The average annual total return figures compare Class R5 and Class R6 share performance to the MSCI Emerging Markets Net Total Return USD Index, which represents a broad measure of equity market performance of emerging markets. Past performance (before and after taxes) is not necessarily an indication of how the Fund will perform in the future. The performance information shown below is as of the calendar year ended December 31, 2021. Updated performance information may be obtained on the Thornburg website at www.thornburg.com or by calling 1-800-847-0200.
Performance Information Illustrates Variability of Returns [Text] rr_PerformanceInformationIllustratesVariabilityOfReturns The following information provides some indication of the risks of investing in Developing World Fund by showing how the Fund’s investment results vary from year to year.
Performance Availability Phone [Text] rr_PerformanceAvailabilityPhone 1-800-847-0200
Performance Availability Website Address [Text] rr_PerformanceAvailabilityWebSiteAddress www.thornburg.com
Performance Past Does Not Indicate Future [Text] rr_PerformancePastDoesNotIndicateFuture Past performance (before and after taxes) is not necessarily an indication of how the Fund will perform in the future.
Bar Chart [Heading] rr_BarChartHeading Annual Total Returns – Class R5 Shares
Bar Chart Closing [Text Block] rr_BarChartClosingTextBlock

Total
Returns

Quarter
ended

Highest Quarterly Results

21.77%

6/30/2020

Lowest Quarterly Results

(24.75)%

3/31/2020
Performance Table Heading rr_PerformanceTableHeading Average Annual Total Returns (periods ended 12-31-21)
Performance Table Uses Highest Federal Rate rr_PerformanceTableUsesHighestFederalRate After-tax returns are calculated using the historical highest individual federal marginal income tax rates, and do not reflect state or local income taxes.
Performance Table Not Relevant to Tax Deferred rr_PerformanceTableNotRelevantToTaxDeferred Actual after-tax returns depend on an investor’s own tax situation and may differ from the returns shown, and after-tax returns shown are not relevant to investors who hold their Fund shares through tax-deferred arrangements, such as 401(k) plans or individual retirement accounts.
Performance Table One Class of after Tax Shown [Text] rr_PerformanceTableOneClassOfAfterTaxShown The after-tax returns shown relate only to Class R5 shares, and after-tax returns for other share classes will vary.
Performance Table Closing [Text Block] rr_PerformanceTableClosingTextBlock

After-tax returns are calculated using the historical highest individual federal marginal income tax rates, and do not reflect state or local income taxes. Actual after-tax returns depend on an investor’s own tax situation and may differ from the returns shown, and after-tax returns shown are not relevant to investors who hold their Fund shares through tax-deferred arrangements, such as 401(k) plans or individual retirement accounts. The after-tax returns shown relate only to Class R5 shares, and after-tax returns for other share classes will vary.
Retirement | Thornburg Developing World Fund | Thornburg Developing World Fund Class R5  
Prospectus [Line Items] rr_ProspectusLineItems  
Trading Symbol dei_TradingSymbol THDRX
Maximum Sales Charge Imposed on Purchases (as a percentage of Offering Price) rr_MaximumSalesChargeImposedOnPurchasesOverOfferingPrice none
Maximum Deferred Sales Charge (as a percentage) rr_MaximumDeferredSalesChargeOverOther none
Management Fees (as a percentage of Assets) rr_ManagementFeesOverAssets 0.94%
Distribution and Service (12b-1) Fees rr_DistributionAndService12b1FeesOverAssets none
Other Expenses (as a percentage of Assets): rr_OtherExpensesOverAssets 0.76%
Expenses (as a percentage of Assets) rr_ExpensesOverAssets 1.70%
Fee Waiver or Reimbursement rr_FeeWaiverOrReimbursementOverAssets (0.66%) [65]
Net Expenses (as a percentage of Assets) rr_NetExpensesOverAssets 1.04%
Expense Example, with Redemption, 1 Year rr_ExpenseExampleYear01 $ 106
Expense Example, with Redemption, 3 Years rr_ExpenseExampleYear03 471
Expense Example, with Redemption, 5 Years rr_ExpenseExampleYear05 861
Expense Example, with Redemption, 10 Years rr_ExpenseExampleYear10 $ 1,954
Annual Return 2014 rr_AnnualReturn2014 (2.69%)
Annual Return 2015 rr_AnnualReturn2015 (14.94%)
Annual Return 2016 rr_AnnualReturn2016 3.08%
Annual Return 2017 rr_AnnualReturn2017 35.84%
Annual Return 2018 rr_AnnualReturn2018 (14.88%)
Annual Return 2019 rr_AnnualReturn2019 29.53%
Annual Return 2020 rr_AnnualReturn2020 23.08%
Annual Return 2021 rr_AnnualReturn2021 (2.65%)
Highest Quarterly Return, Label rr_HighestQuarterlyReturnLabel Highest Quarterly Results
Highest Quarterly Return, Date rr_BarChartHighestQuarterlyReturnDate Jun. 30, 2020
Highest Quarterly Return rr_BarChartHighestQuarterlyReturn 21.77%
Lowest Quarterly Return, Label rr_LowestQuarterlyReturnLabel Lowest Quarterly Results
Lowest Quarterly Return, Date rr_BarChartLowestQuarterlyReturnDate Mar. 31, 2020
Lowest Quarterly Return rr_BarChartLowestQuarterlyReturn (24.75%)
1 Year rr_AverageAnnualReturnYear01 (2.65%)
5 Years rr_AverageAnnualReturnYear05 12.41%
Since Inception rr_AverageAnnualReturnSinceInception 5.91%
Inception Date rr_AverageAnnualReturnInceptionDate Feb. 01, 2013
Retirement | Thornburg Developing World Fund | Thornburg Developing World Fund Class R5 | After Taxes on Distributions  
Prospectus [Line Items] rr_ProspectusLineItems  
1 Year rr_AverageAnnualReturnYear01 (2.65%)
5 Years rr_AverageAnnualReturnYear05 12.07%
Since Inception rr_AverageAnnualReturnSinceInception 5.63%
Retirement | Thornburg Developing World Fund | Thornburg Developing World Fund Class R5 | After Taxes on Distributions and Sales  
Prospectus [Line Items] rr_ProspectusLineItems  
1 Year rr_AverageAnnualReturnYear01 (1.57%)
5 Years rr_AverageAnnualReturnYear05 9.74%
Since Inception rr_AverageAnnualReturnSinceInception 4.56%
Retirement | Thornburg Developing World Fund | Thornburg Developing World Fund Class R5 | MSCI Emerging Markets Index (reflects no deduction for fees, expenses, or U.S. taxes)  
Prospectus [Line Items] rr_ProspectusLineItems  
1 Year rr_AverageAnnualReturnYear01 (2.54%)
5 Years rr_AverageAnnualReturnYear05 9.87%
Since Inception rr_AverageAnnualReturnSinceInception 4.00%
Retirement | Thornburg Developing World Fund | Thornburg Developing World Fund Class R6  
Prospectus [Line Items] rr_ProspectusLineItems  
Trading Symbol dei_TradingSymbol TDWRX
Maximum Sales Charge Imposed on Purchases (as a percentage of Offering Price) rr_MaximumSalesChargeImposedOnPurchasesOverOfferingPrice none
Maximum Deferred Sales Charge (as a percentage) rr_MaximumDeferredSalesChargeOverOther none
Management Fees (as a percentage of Assets) rr_ManagementFeesOverAssets 0.94%
Distribution and Service (12b-1) Fees rr_DistributionAndService12b1FeesOverAssets none
Other Expenses (as a percentage of Assets): rr_OtherExpensesOverAssets 0.17%
Expenses (as a percentage of Assets) rr_ExpensesOverAssets 1.11%
Fee Waiver or Reimbursement rr_FeeWaiverOrReimbursementOverAssets (0.17%) [65]
Net Expenses (as a percentage of Assets) rr_NetExpensesOverAssets 0.94%
Expense Example, with Redemption, 1 Year rr_ExpenseExampleYear01 $ 96
Expense Example, with Redemption, 3 Years rr_ExpenseExampleYear03 336
Expense Example, with Redemption, 5 Years rr_ExpenseExampleYear05 595
Expense Example, with Redemption, 10 Years rr_ExpenseExampleYear10 $ 1,336
1 Year rr_AverageAnnualReturnYear01 (2.56%)
5 Years rr_AverageAnnualReturnYear05 12.52%
Since Inception rr_AverageAnnualReturnSinceInception 6.01%
Inception Date rr_AverageAnnualReturnInceptionDate Feb. 01, 2013
Retirement | Thornburg Developing World Fund | Thornburg Developing World Fund Class R6 | MSCI Emerging Markets Index (reflects no deduction for fees, expenses, or U.S. taxes)  
Prospectus [Line Items] rr_ProspectusLineItems  
1 Year rr_AverageAnnualReturnYear01 (2.54%)
5 Years rr_AverageAnnualReturnYear05 9.87%
Since Inception rr_AverageAnnualReturnSinceInception 4.00%
Retirement | Thornburg Small/Mid Cap Core Fund  
Prospectus [Line Items] rr_ProspectusLineItems  
Risk/Return [Heading] rr_RiskReturnHeading Small/Mid Cap Core Fund
Objective [Heading] rr_ObjectiveHeading Investment Goal
Objective, Primary [Text Block] rr_ObjectivePrimaryTextBlock

The Fund seeks long-term capital appreciation by investing in equity and debt securities of all types.
Objective, Secondary [Text Block] rr_ObjectiveSecondaryTextBlock

The secondary, non-fundamental goal of the Fund is to seek some current income.
Expense [Heading] rr_ExpenseHeading Fees and Expenses of the Fund
Expense Narrative [Text Block] rr_ExpenseNarrativeTextBlock

This table describes the fees and expenses that you may pay if you buy and hold shares of the Fund.
Shareholder Fees Caption [Text] rr_ShareholderFeesCaption Shareholder Fees (fees paid directly from your investment)
Operating Expenses Caption [Text] rr_OperatingExpensesCaption Annual Fund Operating Expenses (expenses that you pay each year as a percentage of the value of your investment)
Fee Waiver or Reimbursement over Assets, Date of Termination rr_FeeWaiverOrReimbursementOverAssetsDateOfTermination February 1, 2023
Portfolio Turnover [Heading] rr_PortfolioTurnoverHeading Portfolio Turnover.
Portfolio Turnover [Text Block] rr_PortfolioTurnoverTextBlock

The Fund pays transaction costs, such as commissions, when it buys and sells securities (or “turns over”) its portfolio. A higher portfolio turnover rate may indicate higher transaction costs and may result in higher taxes when Fund shares are held in a taxable account. These costs, which are not reflected in Annual Fund Operating Expenses or in the Example, affect the Fund’s performance. During the most recent fiscal year, the Fund’s portfolio turnover rate was 135.80% of the average value of its portfolio.
Portfolio Turnover, Rate rr_PortfolioTurnoverRate 135.80%
Expense Example [Heading] rr_ExpenseExampleHeading Example.
Expense Example Narrative [Text Block] rr_ExpenseExampleNarrativeTextBlock

This Example is intended to help you compare the cost of investing in the Fund with the cost of investing in other mutual funds.

The Example assumes that you invest $10,000 in the Fund for the time periods indicated and then redeem all of your shares at the end of those periods. The Example also assumes that your investment has a 5% return each year, dividends and distributions are reinvested, and that the Fund’s operating expenses remain the same. Although your actual costs may be higher or lower, based on these assumptions (and giving effect to fee waivers and expense reimbursements in the first year), your costs would be:
Strategy [Heading] rr_StrategyHeading Principal Investment Strategies
Strategy Narrative [Text Block] rr_StrategyNarrativeTextBlock

Under normal conditions, the Fund invests at least 80% of its net assets in small- and mid-capitalization companies. The Fund currently defines small- and mid-capitalization companies to be those within the market capitalization range comprised by the Russell 2500 Index – Total Return. As of November 30, 2021, the market capitalization range of the Russell 2500 Index – Total Return was approximately $14 million to $33 billion. The market capitalization range of the Russell 2500 Index – Total Return changes over time and, as a result, the capitalization range of companies in which the Fund invests will also change. The Fund may change the definition of what constitutes “small- and mid-capitalization companies” without advance notice to shareholders.

The Fund expects to invest primarily in domestic common stocks. However, the Fund may own foreign common stocks which, in the opinion of the Fund’s investment advisor, Thornburg Investment Management, Inc. (“Thornburg”), offer prospects for meeting the Fund’s investment goals.

With its core approach to stock selection, the Fund seeks to invest in a broadly diversified portfolio of companies the Fund categorizes as basic values, consistent earners, and emerging franchises, as described in more detail below. The relative proportions of securities invested in each of those categories will vary over time.

Thornburg primarily takes a bottom-up, fundamental view in determining the attractiveness of individual securities and in making investment decisions. Among the specific factors considered by Thornburg in identifying securities for inclusion in the Fund are:

•earnings growth potential

•durable business model

•industry growth potential

•innovation driving the potential to disrupt entrenched competitors

•intrinsic value appreciation potential

•potential size of addressable market

•management strength

•leverage

•return on invested capital

•valuation metrics, including: price/earnings (“PE”) ratio; enterprise value/revenue ratio; PE/growth rate ratio, enterprise value/EBITDA (earnings before interest, taxes, depreciation and amortization) ratio; and free cash flow yield.

The Fund categorizes its investments in the following three categories:

Basic Value: Companies generally operating in mature or cyclical industries and which generally exhibit more economic sensitivity and/or higher volatility in earnings and cash flow.

Consistent Earner: Companies which generally exhibit predictable growth and profitability, and consistent cash flow and/or dividends.

Emerging Franchise: Companies with the potential to grow at an above average rate because of a product or service that is establishing a new market and/or taking share from existing participants.

Inclusion of any investment in any of the three described categories represents the opinion of the advisor concerning the characteristics and prospects of the investment. There is no assurance that any company selected for investment will, once categorized in one of the three described investment categories, continue to have the positive characteristics or fulfill the expectations that the advisor had for the company when it was selected for investment, and any such company may not grow or may decline in earnings and size.

The Fund selects foreign securities issued by companies domiciled in countries whose currencies are freely convertible into U.S. dollars, or in companies in other countries whose business is conducted primarily in U.S. dollars.

The Fund may sell an investment if Thornburg has identified a better investment opportunity, in response to changes in the conditions or business of the investment’s issuer or changes in overall market conditions, if Thornburg has a target price for the investment and that target price has been achieved, or if, in Thornburg’s opinion, the investment no longer serves to achieve the Fund’s investment goals.

The Fund’s policy of investing at least 80% of its assets in small- and mid-capitalization companies may be changed by the Fund’s Trustees without a shareholder vote upon 60 days’ notice to shareholders.
Risk [Heading] rr_RiskHeading Principal Investment Risks
Risk Narrative [Text Block] rr_RiskNarrativeTextBlock

An investment in the Fund is not a deposit in any bank and is not insured or guaranteed by the Federal Deposit Insurance Corporation or any other governmental agency. Accordingly, the loss of money is a risk of investing in the Fund. The value of the Fund’s shares varies from day to day and over time, and when you sell your shares they may be worth less than what you paid for them. The following is a summary of the principal risks of investing in the Fund.

Management Risk – The Fund is an actively managed portfolio, and the value of the Fund may be reduced if Thornburg pursues unsuccessful investments or fails to correctly identify risks affecting the broad economy or specific issuers in which the Fund invests.

Market and Economic Risk – The value of the Fund’s investments may decline and its share value may be reduced due to changes in general economic and market conditions. The value of a security may change in response to developments affecting entire economies, markets or industries, including changes in interest rates, political and legal developments, and general market volatility.

Equity Risk – The value of the Fund’s equity investments may fluctuate significantly over time in response to factors affecting individual issuers, particular industries, or the market as a whole. Additionally, common stock ranks below preferred stock and debt securities in claims for dividends and for assets of a company in a liquidation or bankruptcy.

Risks Affecting Specific Issuers – The value of an equity security may decline in response to developments affecting the specific issuer of the security or obligation, even if the overall industry or economy is unaffected. These developments may include a variety of factors, including but not limited to management issues or other corporate disruption, a decline in revenues or profitability, an increase in costs, or an adverse effect on the issuer’s competitive position.

Small and Mid-Cap Company Risk – Investments in small-capitalization companies and mid-capitalization companies may involve additional risks, which may be relatively higher with smaller companies. These additional risks may result from limited product lines, earlier stages of development and lack of well-established businesses, more limited access to markets and financial resources, greater vulnerability to competition and market risks and fluctuations, lack of management depth, increased volatility in share price, and possible difficulties in valuing or selling these investments. Relative to the stocks of large capitalization companies, the stocks of small- and mid-capitalization companies may be thinly traded and sales may result in higher transaction costs. Also, small- and mid-capitalization companies may perform poorly during times of economic stress.

Foreign Investment Risk – Investments in securities of foreign issuers may involve risks including adverse fluctuations in currency exchange rates, political instability, confiscations, taxes or restrictions on currency exchange, difficulty in selling foreign investments, and reduced legal protection.

Liquidity Risk – Due to a lack of demand in the marketplace or other factors, the Fund may not be able to sell some or all of its investments promptly, or may only be able to sell investments at less than desired prices.

Cybersecurity and Operational Risk – Operational failures, cyber-attacks or other disruptions that affect the Fund’s service providers, the Fund’s counterparties, other market participants or the issuers of securities held by the Fund may adversely affect the Fund and its shareholders, including by causing losses for the Fund or impairing Fund operations.

Additional information about Fund investments, investment strategies, and risks of investing in the Fund appears beginning on page 61 of the Prospectus.
Risk Lose Money [Text] rr_RiskLoseMoney Accordingly, the loss of money is a risk of investing in the Fund.
RIsk Not Insured [Text] rr_RiskNotInsured An investment in the Fund is not a deposit in any bank and is not insured or guaranteed by the Federal Deposit Insurance Corporation or any other governmental agency.
Bar Chart and Performance Table [Heading] rr_BarChartAndPerformanceTableHeading Past Performance of the Fund
Performance Narrative [Text Block] rr_PerformanceNarrativeTextBlock

The following information provides some indication of the risks of investing in the Small/Mid Cap Core Fund by showing how the Fund’s investment results vary from year to year. The bar chart shows how the annual total returns for Class R3 shares have been different in each full year shown. The average annual total return figures compare Class R3, Class R4 and Class R5 share performance to Russell 2500 Index—Total Return, a broad measure of market performance. Past performance (before and after taxes) is not necessarily an indication of how the Fund will perform in the future. The performance information shown below is as of the calendar year ended December 31, 2021. Updated performance information may be obtained on the Thornburg website at www.thornburg.com or by calling 1-800-847-0200.
Performance Information Illustrates Variability of Returns [Text] rr_PerformanceInformationIllustratesVariabilityOfReturns The following information provides some indication of the risks of investing in the Small/Mid Cap Core Fund by showing how the Fund’s investment results vary from year to year.
Performance Availability Phone [Text] rr_PerformanceAvailabilityPhone 1-800-847-0200
Performance Availability Website Address [Text] rr_PerformanceAvailabilityWebSiteAddress www.thornburg.com
Performance Past Does Not Indicate Future [Text] rr_PerformancePastDoesNotIndicateFuture Past performance (before and after taxes) is not necessarily an indication of how the Fund will perform in the future.
Bar Chart [Heading] rr_BarChartHeading Annual Total Returns – Class R3 Shares
Bar Chart Closing [Text Block] rr_BarChartClosingTextBlock

Total
Returns

Quarter
ended

Highest Quarterly Results

18.90%

6/30/2020

Lowest Quarterly Results

(26.31)%

3/31/2020
Performance Table Heading rr_PerformanceTableHeading Average Annual Total Returns (periods ended 12-31-21)
Performance Table Uses Highest Federal Rate rr_PerformanceTableUsesHighestFederalRate After-tax returns are calculated using the highest historical individual federal marginal income tax rates, and do not reflect state or local income taxes.
Performance Table Not Relevant to Tax Deferred rr_PerformanceTableNotRelevantToTaxDeferred Actual after-tax returns depend on an investor’s own tax situation and may differ from the returns shown, and after-tax returns shown are not relevant to investors who hold their Fund shares through tax-deferred arrangements, such as 401(k) plans or individual retirement accounts.
Performance Table One Class of after Tax Shown [Text] rr_PerformanceTableOneClassOfAfterTaxShown The after-tax returns shown relate only to Class R3 shares, and after-tax returns for other share classes will vary.
Performance Table Closing [Text Block] rr_PerformanceTableClosingTextBlock

After-tax returns are calculated using the highest historical individual federal marginal income tax rates, and do not reflect state or local income taxes. Actual after-tax returns depend on an investor’s own tax situation and may differ from the returns shown, and after-tax returns shown are not relevant to investors who hold their Fund shares through tax-deferred arrangements, such as 401(k) plans or individual retirement accounts. The after-tax returns shown relate only to Class R3 shares, and after-tax returns for other share classes will vary.

The performance information shown above may include gains attributable to the Fund’s investments in shares of companies through initial public offerings (“IPOs”). There can be no assurance that the Fund will have continued access to profitable IPOs and, as the Fund’s assets grow, the impact of the Fund’s investment in IPOs on the performance of the Fund may decline.
Retirement | Thornburg Small/Mid Cap Core Fund | Thornburg Small/Mid Cap Core Fund - Class R3  
Prospectus [Line Items] rr_ProspectusLineItems  
Trading Symbol dei_TradingSymbol TVRFX
Maximum Sales Charge Imposed on Purchases (as a percentage of Offering Price) rr_MaximumSalesChargeImposedOnPurchasesOverOfferingPrice none
Maximum Deferred Sales Charge (as a percentage) rr_MaximumDeferredSalesChargeOverOther none
Management Fees (as a percentage of Assets) rr_ManagementFeesOverAssets 0.85%
Distribution and Service (12b-1) Fees rr_DistributionAndService12b1FeesOverAssets 0.50%
Other Expenses (as a percentage of Assets): rr_OtherExpensesOverAssets 0.44% [66]
Expenses (as a percentage of Assets) rr_ExpensesOverAssets 1.79%
Fee Waiver or Reimbursement rr_FeeWaiverOrReimbursementOverAssets (0.48%) [67]
Net Expenses (as a percentage of Assets) rr_NetExpensesOverAssets 1.31%
Expense Example, with Redemption, 1 Year rr_ExpenseExampleYear01 $ 133
Expense Example, with Redemption, 3 Years rr_ExpenseExampleYear03 517
Expense Example, with Redemption, 5 Years rr_ExpenseExampleYear05 925
Expense Example, with Redemption, 10 Years rr_ExpenseExampleYear10 $ 2,066
Annual Return 2012 rr_AnnualReturn2012 10.66%
Annual Return 2013 rr_AnnualReturn2013 39.56%
Annual Return 2014 rr_AnnualReturn2014 11.51%
Annual Return 2015 rr_AnnualReturn2015 3.45%
Annual Return 2016 rr_AnnualReturn2016 6.65%
Annual Return 2017 rr_AnnualReturn2017 23.35%
Annual Return 2018 rr_AnnualReturn2018 (9.72%)
Annual Return 2019 rr_AnnualReturn2019 28.86%
Annual Return 2020 rr_AnnualReturn2020 11.70%
Annual Return 2021 rr_AnnualReturn2021 13.78%
Highest Quarterly Return, Label rr_HighestQuarterlyReturnLabel Highest Quarterly Results
Highest Quarterly Return, Date rr_BarChartHighestQuarterlyReturnDate Jun. 30, 2020
Highest Quarterly Return rr_BarChartHighestQuarterlyReturn 18.90%
Lowest Quarterly Return, Label rr_LowestQuarterlyReturnLabel Lowest Quarterly Results
Lowest Quarterly Return, Date rr_BarChartLowestQuarterlyReturnDate Mar. 31, 2020
Lowest Quarterly Return rr_BarChartLowestQuarterlyReturn (26.31%)
1 Year rr_AverageAnnualReturnYear01 13.78%
5 Years rr_AverageAnnualReturnYear05 12.77%
10 Years rr_AverageAnnualReturnYear10 13.23%
Retirement | Thornburg Small/Mid Cap Core Fund | Thornburg Small/Mid Cap Core Fund - Class R3 | After Taxes on Distributions  
Prospectus [Line Items] rr_ProspectusLineItems  
1 Year rr_AverageAnnualReturnYear01 5.06%
5 Years rr_AverageAnnualReturnYear05 10.88%
10 Years rr_AverageAnnualReturnYear10 12.23%
Retirement | Thornburg Small/Mid Cap Core Fund | Thornburg Small/Mid Cap Core Fund - Class R3 | After Taxes on Distributions and Sales  
Prospectus [Line Items] rr_ProspectusLineItems  
1 Year rr_AverageAnnualReturnYear01 11.89%
5 Years rr_AverageAnnualReturnYear05 9.85%
10 Years rr_AverageAnnualReturnYear10 10.91%
Retirement | Thornburg Small/Mid Cap Core Fund | Thornburg Small/Mid Cap Core Fund - Class R3 | Russell 2500 Index-Total Return (reflects no deduction for fees, expenses, or taxes)  
Prospectus [Line Items] rr_ProspectusLineItems  
1 Year rr_AverageAnnualReturnYear01 18.18%
5 Years rr_AverageAnnualReturnYear05 13.75%
10 Years rr_AverageAnnualReturnYear10 14.15%
Retirement | Thornburg Small/Mid Cap Core Fund | Thornburg Small/Mid Cap Core Fund - Class R4  
Prospectus [Line Items] rr_ProspectusLineItems  
Trading Symbol dei_TradingSymbol TVIRX
Maximum Sales Charge Imposed on Purchases (as a percentage of Offering Price) rr_MaximumSalesChargeImposedOnPurchasesOverOfferingPrice none
Maximum Deferred Sales Charge (as a percentage) rr_MaximumDeferredSalesChargeOverOther none
Management Fees (as a percentage of Assets) rr_ManagementFeesOverAssets 0.85%
Distribution and Service (12b-1) Fees rr_DistributionAndService12b1FeesOverAssets 0.25%
Other Expenses (as a percentage of Assets): rr_OtherExpensesOverAssets 0.66% [66]
Expenses (as a percentage of Assets) rr_ExpensesOverAssets 1.76%
Fee Waiver or Reimbursement rr_FeeWaiverOrReimbursementOverAssets (0.55%) [67]
Net Expenses (as a percentage of Assets) rr_NetExpensesOverAssets 1.21%
Expense Example, with Redemption, 1 Year rr_ExpenseExampleYear01 $ 123
Expense Example, with Redemption, 3 Years rr_ExpenseExampleYear03 501
Expense Example, with Redemption, 5 Years rr_ExpenseExampleYear05 903
Expense Example, with Redemption, 10 Years rr_ExpenseExampleYear10 $ 2,028
1 Year rr_AverageAnnualReturnYear01 13.90%
5 Years rr_AverageAnnualReturnYear05 12.88%
10 Years rr_AverageAnnualReturnYear10 13.35%
Retirement | Thornburg Small/Mid Cap Core Fund | Thornburg Small/Mid Cap Core Fund - Class R4 | Russell 2500 Index-Total Return (reflects no deduction for fees, expenses, or taxes)  
Prospectus [Line Items] rr_ProspectusLineItems  
1 Year rr_AverageAnnualReturnYear01 18.18%
5 Years rr_AverageAnnualReturnYear05 13.75%
10 Years rr_AverageAnnualReturnYear10 14.15%
Retirement | Thornburg Small/Mid Cap Core Fund | Thornburg Small/Mid Cap Core Fund - Class R5  
Prospectus [Line Items] rr_ProspectusLineItems  
Trading Symbol dei_TradingSymbol TVRRX
Maximum Sales Charge Imposed on Purchases (as a percentage of Offering Price) rr_MaximumSalesChargeImposedOnPurchasesOverOfferingPrice none
Maximum Deferred Sales Charge (as a percentage) rr_MaximumDeferredSalesChargeOverOther none
Management Fees (as a percentage of Assets) rr_ManagementFeesOverAssets 0.85%
Distribution and Service (12b-1) Fees rr_DistributionAndService12b1FeesOverAssets none
Other Expenses (as a percentage of Assets): rr_OtherExpensesOverAssets 0.61% [66]
Expenses (as a percentage of Assets) rr_ExpensesOverAssets 1.46%
Fee Waiver or Reimbursement rr_FeeWaiverOrReimbursementOverAssets (0.51%) [67]
Net Expenses (as a percentage of Assets) rr_NetExpensesOverAssets 0.95%
Expense Example, with Redemption, 1 Year rr_ExpenseExampleYear01 $ 97
Expense Example, with Redemption, 3 Years rr_ExpenseExampleYear03 412
Expense Example, with Redemption, 5 Years rr_ExpenseExampleYear05 749
Expense Example, with Redemption, 10 Years rr_ExpenseExampleYear10 $ 1,703
1 Year rr_AverageAnnualReturnYear01 14.19%
5 Years rr_AverageAnnualReturnYear05 13.18%
10 Years rr_AverageAnnualReturnYear10 13.64%
Retirement | Thornburg Small/Mid Cap Core Fund | Thornburg Small/Mid Cap Core Fund - Class R5 | Russell 2500 Index-Total Return (reflects no deduction for fees, expenses, or taxes)  
Prospectus [Line Items] rr_ProspectusLineItems  
1 Year rr_AverageAnnualReturnYear01 18.18%
5 Years rr_AverageAnnualReturnYear05 13.75%
10 Years rr_AverageAnnualReturnYear10 14.15%
Retirement | Thornburg Small/Mid Cap Growth Fund  
Prospectus [Line Items] rr_ProspectusLineItems  
Risk/Return [Heading] rr_RiskReturnHeading Small/Mid Cap Growth Fund
Objective [Heading] rr_ObjectiveHeading Investment Goal
Objective, Primary [Text Block] rr_ObjectivePrimaryTextBlock

The Fund seeks long-term growth of capital by investing in equity securities selected for their growth potential.

Expense [Heading] rr_ExpenseHeading Fees and Expenses of the Fund
Expense Narrative [Text Block] rr_ExpenseNarrativeTextBlock

This table describes the fees and expenses that you may pay if you buy and hold shares of the Fund.
Shareholder Fees Caption [Text] rr_ShareholderFeesCaption Shareholder Fees (fees paid directly from your investment)
Operating Expenses Caption [Text] rr_OperatingExpensesCaption Annual Fund Operating Expenses (expenses that you pay each year as a percentage of the value of your investment)
Fee Waiver or Reimbursement over Assets, Date of Termination rr_FeeWaiverOrReimbursementOverAssetsDateOfTermination February 1, 2023
Portfolio Turnover [Heading] rr_PortfolioTurnoverHeading Portfolio Turnover.
Portfolio Turnover [Text Block] rr_PortfolioTurnoverTextBlock

The Fund pays transaction costs, such as commissions, when it buys and sells securities (or “turns over”) its portfolio. A higher portfolio turnover rate may indicate higher transaction costs and may result in higher taxes when Fund shares are held in a taxable account. These costs, which are not reflected in Annual Fund Operating Expenses or in the Example, affect the Fund’s performance. During the most recent fiscal year, the Fund’s portfolio turnover rate was 161.43% of the average value of its portfolio.
Portfolio Turnover, Rate rr_PortfolioTurnoverRate 161.43%
Expense Example [Heading] rr_ExpenseExampleHeading Example.
Expense Example Narrative [Text Block] rr_ExpenseExampleNarrativeTextBlock

This Example is intended to help you compare the cost of investing in the Fund with the cost of investing in other mutual funds.

The Example assumes that you invest $10,000 in the Fund for the time periods indicated and then redeem all of your shares at the end of those periods. The Example also assumes that your investment has a 5% return each year, dividends and distributions are reinvested, and that the Fund’s operating expenses remain the same. Although your actual costs may be higher or lower, based on these assumptions (and giving effect to fee waivers and expense reimbursements in the first year), your costs would be:
Strategy [Heading] rr_StrategyHeading Principal Investment Strategies
Strategy Narrative [Text Block] rr_StrategyNarrativeTextBlock

Under normal conditions, the Fund invests at least 80% of its net assets in small- and mid-capitalization companies. The Fund currently defines small- and mid-capitalization companies to be those within the market capitalization range comprised by the Russell 2500 Growth Index – Total Return. As of November 30, 2021, the market capitalization range of the Russell 2500 Growth Index – Total Return was approximately $5 million to $33 billion. The market capitalization range of the Russell 2500 Growth Index – Total Return changes over time and, as a result, the capitalization range of companies in which the Fund invests will also change. The Fund may change the definition of what constitutes “small- and mid-capitalization companies” without advance notice to shareholders.

The Fund expects to invest primarily in domestic common stocks. However, the Fund may own foreign common stocks which, in the opinion of the Fund’s investment advisor, Thornburg Investment Management, Inc. (“Thornburg”), offer prospects for meeting the Fund’s investment goal.

The Fund seeks to invest in a diversified portfolio of companies the Fund categorizes as consistent growers, disruptors, and emerging franchises, as described in more detail below. The relative proportions of securities invested in each of those categories will vary over time.

Thornburg primarily takes a bottom-up, fundamental view in determining the attractiveness of individual securities and in making investment decisions. Among the specific factors considered by Thornburg in identifying securities for inclusion in the Fund are:

•earnings growth potential

•durable business model

•industry growth potential

•innovation driving the potential to disrupt entrenched competitors

•intrinsic value appreciation potential

•potential size of addressable market

•management strength

•leverage

•return on invested capital

•valuation metrics, including: price/earnings (“PE”) ratio; enterprise value/revenue ratio; PE/growth rate ratio, enterprise value/EBITDA (earnings before interest, taxes, depreciation and amortization) ratio; and free cash flow yield.

The Fund categorizes its equity investments in the following three categories:

Consistent Growers: Companies in this category generally exhibit steady earnings or revenue growth, or both. These companies may have subscription or other recurring revenue profiles. Given their business models, these companies may outperform in weak markets.

Disruptors: Companies which are at the early stages of growth; which usually possess highly innovative or differentiated products and services, but which may require substantial additional time or investment to capitalize on market opportunities and achieve profitability. Companies in this category often are in leadership positions in growing markets. These companies may operate in niche markets with large or dominant share.

Emerging Franchises: Companies with the potential to grow at an above average rate because of a product or service that is establishing a new market and/or taking share from existing participants.

Inclusion of any investment in any of the three described categories represents the opinion of the advisor concerning the characteristics and prospects of the investment. There is no assurance that any company selected for investment will, once categorized in one of the three described investment categories, continue to have the positive characteristics or fulfill the expectations that the advisor had for the company when it was selected for investment, and any such company may not grow or may decline in earnings and size.

The Fund selects foreign securities issued by companies domiciled in countries whose currencies are freely convertible into U.S. dollars, or in companies in other countries whose business is conducted primarily in U.S. dollars.

The Fund may sell an investment if Thornburg has identified a better investment opportunity, in response to changes in the conditions or business of the investment’s issuer or changes in overall market conditions, if Thornburg has a target price for the investment and that target price has been achieved, or if, in Thornburg’s opinion, the investment no longer serves to achieve the Fund’s investment goals.

The Fund’s policy of investing at least 80% of its assets in small- and mid-capitalization companies may be changed by the Fund’s Trustees without a shareholder vote upon 60 days’ notice to shareholders.
Risk [Heading] rr_RiskHeading Principal Investment Risks
Risk Narrative [Text Block] rr_RiskNarrativeTextBlock

An investment in the Fund is not a deposit in any bank and is not insured or guaranteed by the Federal Deposit Insurance Corporation or any other governmental agency. Accordingly, the loss of money is a risk of investing in the Fund. The value of the Fund’s shares varies from day to day and over time, and when you sell your shares they may be worth less than what you paid for them. The following is a summary of the principal risks of investing in the Fund.

Management Risk – The Fund is an actively managed portfolio, and the value of the Fund may be reduced if Thornburg pursues unsuccessful investments or fails to correctly identify risks affecting the broad economy or specific issuers in which the Fund invests.

Market and Economic Risk – The value of the Fund’s investments may decline and its share value may be reduced due to changes in general economic and market conditions. The value of a security may change in response to developments affecting entire economies, markets or industries, including changes in interest rates, political and legal developments, and general market volatility.

Equity Risk – The value of the Fund’s equity investments may fluctuate significantly over time in response to factors affecting individual issuers, particular industries, or the market as a whole. Additionally, common stock ranks below preferred stock and debt securities in claims for dividends and for assets of a company in a liquidation or bankruptcy.

Risks Affecting Specific Issuers – The value of a security may decline in response to developments affecting the specific issuer of the security, even if the overall industry or economy is unaffected. These developments may include a variety of factors, including but not limited to management issues or other corporate disruption, a decline in revenues or profitability, an increase in costs, or an adverse effect on the issuer’s competitive position.

Small and Mid-Cap Company Risk – Investments in small-capitalization companies and mid-capitalization companies may involve additional risks, which may be relatively higher with smaller companies. These additional risks may result from limited product lines, earlier stages of development and lack of well-established businesses, more limited access to markets

and financial resources, greater vulnerability to competition and market risks and fluctuations, lack of management depth, increased volatility in share price, and possible difficulties in valuing or selling these investments. Relative to the stocks of large capitalization companies, the stocks of small- and mid-capitalization companies may be thinly traded and sales may result in higher transaction costs. Also, small- and mid-capitalization companies may perform poorly during times of economic stress.

Foreign Investment Risk – Investments in securities of foreign issuers may involve risks including adverse fluctuations in currency exchange rates, political instability, confiscations, taxes or restrictions on currency exchange, difficulty in selling foreign investments, and reduced legal protection.

Liquidity Risk – Due to a lack of demand in the marketplace or other factors, the Fund may not be able to sell some or all of its investments promptly, or may only be able to sell investments at less than desired prices.

Cybersecurity and Operational Risk – Operational failures, cyber-attacks or other disruptions that affect the Fund’s service providers, the Fund’s counterparties, other market participants or the issuers of securities held by the Fund may adversely affect the Fund and its shareholders, including by causing losses for the Fund or impairing Fund operations.

Additional information about Fund investments, investment strategies, and risks of investing in the Fund appears beginning on page 61 of the Prospectus.
Risk Lose Money [Text] rr_RiskLoseMoney Accordingly, the loss of money is a risk of investing in the Fund.
RIsk Not Insured [Text] rr_RiskNotInsured An investment in the Fund is not a deposit in any bank and is not insured or guaranteed by the Federal Deposit Insurance Corporation or any other governmental agency.
Bar Chart and Performance Table [Heading] rr_BarChartAndPerformanceTableHeading Past Performance of the Fund
Performance Narrative [Text Block] rr_PerformanceNarrativeTextBlock

The following information provides some indication of the risks of investing in the Small/Mid Cap Growth Fund by showing how the Fund’s investment results vary from year to year. The bar chart shows how the annual total returns for Class R3 shares vary in each full year shown. The average annual total return figures compare Class R3, Class R4 and Class R5 share performance to the Russell 2500 Growth Index—Total Return, a broad measure of market performance. Past performance (before and after taxes) is not necessarily an indication of how the Fund will perform in the future. The performance information shown below is as of the calendar year ended December 31, 2021. Updated performance information may be obtained on the Thornburg website at www.thornburg.com or by calling 1-800-847-0200.

Performance Information Illustrates Variability of Returns [Text] rr_PerformanceInformationIllustratesVariabilityOfReturns The following information provides some indication of the risks of investing in the Small/Mid Cap Growth Fund by showing how the Fund’s investment results vary from year to year.
Performance Availability Phone [Text] rr_PerformanceAvailabilityPhone 1-800-847-0200
Performance Availability Website Address [Text] rr_PerformanceAvailabilityWebSiteAddress www.thornburg.com
Performance Past Does Not Indicate Future [Text] rr_PerformancePastDoesNotIndicateFuture Past performance (before and after taxes) is not necessarily an indication of how the Fund will perform in the future.
Bar Chart [Heading] rr_BarChartHeading Annual Total Returns – Class R3 Shares
Bar Chart Closing [Text Block] rr_BarChartClosingTextBlock

Total
Returns

Quarter
ended

Highest Quarterly Results

30.91%

6/30/2020

Lowest Quarterly Results

(18.72)%

9/30/2011
Performance Table Heading rr_PerformanceTableHeading Average Annual Total Returns (periods ended 12-31-21)
Performance Table Uses Highest Federal Rate rr_PerformanceTableUsesHighestFederalRate After-tax returns are calculated using the highest historical individual federal marginal income tax rates, and do not reflect state or local income taxes.
Performance Table Not Relevant to Tax Deferred rr_PerformanceTableNotRelevantToTaxDeferred Actual after-tax returns depend on an investor’s own tax situation and may differ from the returns shown, and after-tax returns shown are not relevant to investors who hold their Fund shares through tax-deferred arrangements, such as 401(k) plans or individual retirement accounts.
Performance Table One Class of after Tax Shown [Text] rr_PerformanceTableOneClassOfAfterTaxShown The after-tax returns shown relate only to Class R3 shares, and after-tax returns for other share classes will vary.
Performance Table Closing [Text Block] rr_PerformanceTableClosingTextBlock

After-tax returns are calculated using the highest historical individual federal marginal income tax rates, and do not reflect state or local income taxes. Actual after-tax returns depend on an investor’s own tax situation and may differ from the returns shown, and after-tax returns shown are not relevant to investors who hold their Fund shares through tax-deferred arrangements, such as 401(k) plans or individual retirement accounts. The after-tax returns shown relate only to Class R3 shares, and after-tax returns for other share classes will vary.
Retirement | Thornburg Small/Mid Cap Growth Fund | Thornburg Small/Mid Cap Growth Fund - Class R3  
Prospectus [Line Items] rr_ProspectusLineItems  
Trading Symbol dei_TradingSymbol THCRX
Maximum Sales Charge Imposed on Purchases (as a percentage of Offering Price) rr_MaximumSalesChargeImposedOnPurchasesOverOfferingPrice none
Maximum Deferred Sales Charge (as a percentage) rr_MaximumDeferredSalesChargeOverOther none
Management Fees (as a percentage of Assets) rr_ManagementFeesOverAssets 0.86%
Distribution and Service (12b-1) Fees rr_DistributionAndService12b1FeesOverAssets 0.50%
Other Expenses (as a percentage of Assets): rr_OtherExpensesOverAssets 0.43%
Expenses (as a percentage of Assets) rr_ExpensesOverAssets 1.79%
Fee Waiver or Reimbursement rr_FeeWaiverOrReimbursementOverAssets (0.33%) [68]
Net Expenses (as a percentage of Assets) rr_NetExpensesOverAssets 1.46%
Expense Example, with Redemption, 1 Year rr_ExpenseExampleYear01 $ 149
Expense Example, with Redemption, 3 Years rr_ExpenseExampleYear03 531
Expense Example, with Redemption, 5 Years rr_ExpenseExampleYear05 939
Expense Example, with Redemption, 10 Years rr_ExpenseExampleYear10 $ 2,078
Annual Return 2012 rr_AnnualReturn2012 21.36%
Annual Return 2013 rr_AnnualReturn2013 42.45%
Annual Return 2014 rr_AnnualReturn2014 none
Annual Return 2015 rr_AnnualReturn2015 2.68%
Annual Return 2016 rr_AnnualReturn2016 (2.46%)
Annual Return 2017 rr_AnnualReturn2017 23.79%
Annual Return 2018 rr_AnnualReturn2018 (2.72%)
Annual Return 2019 rr_AnnualReturn2019 28.72%
Annual Return 2020 rr_AnnualReturn2020 41.38%
Annual Return 2021 rr_AnnualReturn2021 (4.47%)
Highest Quarterly Return, Label rr_HighestQuarterlyReturnLabel Highest Quarterly Results
Highest Quarterly Return, Date rr_BarChartHighestQuarterlyReturnDate Jun. 30, 2020
Highest Quarterly Return rr_BarChartHighestQuarterlyReturn 30.91%
Lowest Quarterly Return, Label rr_LowestQuarterlyReturnLabel Lowest Quarterly Results
Lowest Quarterly Return, Date rr_BarChartLowestQuarterlyReturnDate Sep. 30, 2011
Lowest Quarterly Return rr_BarChartLowestQuarterlyReturn (18.72%)
1 Year rr_AverageAnnualReturnYear01 (4.47%)
5 Years rr_AverageAnnualReturnYear05 15.92%
10 Years rr_AverageAnnualReturnYear10 13.74%
Retirement | Thornburg Small/Mid Cap Growth Fund | Thornburg Small/Mid Cap Growth Fund - Class R3 | After Taxes on Distributions  
Prospectus [Line Items] rr_ProspectusLineItems  
1 Year rr_AverageAnnualReturnYear01 (12.29%)
5 Years rr_AverageAnnualReturnYear05 13.08%
10 Years rr_AverageAnnualReturnYear10 12.34%
Retirement | Thornburg Small/Mid Cap Growth Fund | Thornburg Small/Mid Cap Growth Fund - Class R3 | After Taxes on Distributions and Sales  
Prospectus [Line Items] rr_ProspectusLineItems  
1 Year rr_AverageAnnualReturnYear01 3.54%
5 Years rr_AverageAnnualReturnYear05 12.80%
10 Years rr_AverageAnnualReturnYear10 11.57%
Retirement | Thornburg Small/Mid Cap Growth Fund | Thornburg Small/Mid Cap Growth Fund - Class R3 | Russell 2500 Growth Index-Total Return (reflects no deduction for fees, expenses, or taxes)  
Prospectus [Line Items] rr_ProspectusLineItems  
1 Year rr_AverageAnnualReturnYear01 5.04%
5 Years rr_AverageAnnualReturnYear05 17.65%
10 Years rr_AverageAnnualReturnYear10 15.75%
Retirement | Thornburg Small/Mid Cap Growth Fund | Thornburg Small/Mid Cap Growth Fund - Class R4  
Prospectus [Line Items] rr_ProspectusLineItems  
Trading Symbol dei_TradingSymbol TCGRX
Maximum Sales Charge Imposed on Purchases (as a percentage of Offering Price) rr_MaximumSalesChargeImposedOnPurchasesOverOfferingPrice none
Maximum Deferred Sales Charge (as a percentage) rr_MaximumDeferredSalesChargeOverOther none
Management Fees (as a percentage of Assets) rr_ManagementFeesOverAssets 0.86%
Distribution and Service (12b-1) Fees rr_DistributionAndService12b1FeesOverAssets 0.25%
Other Expenses (as a percentage of Assets): rr_OtherExpensesOverAssets 1.06%
Expenses (as a percentage of Assets) rr_ExpensesOverAssets 2.17%
Fee Waiver or Reimbursement rr_FeeWaiverOrReimbursementOverAssets (0.81%) [68]
Net Expenses (as a percentage of Assets) rr_NetExpensesOverAssets 1.36%
Expense Example, with Redemption, 1 Year rr_ExpenseExampleYear01 $ 138
Expense Example, with Redemption, 3 Years rr_ExpenseExampleYear03 601
Expense Example, with Redemption, 5 Years rr_ExpenseExampleYear05 1,090
Expense Example, with Redemption, 10 Years rr_ExpenseExampleYear10 $ 2,440
1 Year rr_AverageAnnualReturnYear01 (4.38%)
5 Years rr_AverageAnnualReturnYear05 16.04%
10 Years rr_AverageAnnualReturnYear10 13.86%
Retirement | Thornburg Small/Mid Cap Growth Fund | Thornburg Small/Mid Cap Growth Fund - Class R4 | Russell 2500 Growth Index-Total Return (reflects no deduction for fees, expenses, or taxes)  
Prospectus [Line Items] rr_ProspectusLineItems  
1 Year rr_AverageAnnualReturnYear01 5.04%
5 Years rr_AverageAnnualReturnYear05 17.65%
10 Years rr_AverageAnnualReturnYear10 15.75%
Retirement | Thornburg Small/Mid Cap Growth Fund | Thornburg Small/Mid Cap Growth Fund - Class R5  
Prospectus [Line Items] rr_ProspectusLineItems  
Trading Symbol dei_TradingSymbol THGRX
Maximum Sales Charge Imposed on Purchases (as a percentage of Offering Price) rr_MaximumSalesChargeImposedOnPurchasesOverOfferingPrice none
Maximum Deferred Sales Charge (as a percentage) rr_MaximumDeferredSalesChargeOverOther none
Management Fees (as a percentage of Assets) rr_ManagementFeesOverAssets 0.86%
Distribution and Service (12b-1) Fees rr_DistributionAndService12b1FeesOverAssets none
Other Expenses (as a percentage of Assets): rr_OtherExpensesOverAssets 0.45%
Expenses (as a percentage of Assets) rr_ExpensesOverAssets 1.31%
Fee Waiver or Reimbursement rr_FeeWaiverOrReimbursementOverAssets (0.36%) [68]
Net Expenses (as a percentage of Assets) rr_NetExpensesOverAssets 0.95%
Expense Example, with Redemption, 1 Year rr_ExpenseExampleYear01 $ 97
Expense Example, with Redemption, 3 Years rr_ExpenseExampleYear03 380
Expense Example, with Redemption, 5 Years rr_ExpenseExampleYear05 684
Expense Example, with Redemption, 10 Years rr_ExpenseExampleYear10 $ 1,548
1 Year rr_AverageAnnualReturnYear01 (4.00%)
5 Years rr_AverageAnnualReturnYear05 16.51%
10 Years rr_AverageAnnualReturnYear10 14.32%
Retirement | Thornburg Small/Mid Cap Growth Fund | Thornburg Small/Mid Cap Growth Fund - Class R5 | Russell 2500 Growth Index-Total Return (reflects no deduction for fees, expenses, or taxes)  
Prospectus [Line Items] rr_ProspectusLineItems  
1 Year rr_AverageAnnualReturnYear01 5.04%
5 Years rr_AverageAnnualReturnYear05 17.65%
10 Years rr_AverageAnnualReturnYear10 15.75%
Retirement | Thornburg Investment Income Builder Fund  
Prospectus [Line Items] rr_ProspectusLineItems  
Risk/Return [Heading] rr_RiskReturnHeading Income Builder Fund
Objective [Heading] rr_ObjectiveHeading Investment Goal
Objective, Primary [Text Block] rr_ObjectivePrimaryTextBlock

The Fund’s primary investment goal is to provide a level of current income which exceeds the average yield on U.S. stocks generally, and which will generally grow, subject to periodic fluctuations, over the years on a per share basis.
Objective, Secondary [Text Block] rr_ObjectiveSecondaryTextBlock

The Fund’s secondary investment goal is long-term capital appreciation.
Expense [Heading] rr_ExpenseHeading Fees and Expenses of the Fund
Expense Narrative [Text Block] rr_ExpenseNarrativeTextBlock

This table describes the fees and expenses that you may pay if you buy and hold shares of the Fund.
Shareholder Fees Caption [Text] rr_ShareholderFeesCaption Shareholder Fees (fees paid directly from your investment)
Operating Expenses Caption [Text] rr_OperatingExpensesCaption Annual Fund Operating Expenses (expenses that you pay each year as a percentage of the value of your investment)
Fee Waiver or Reimbursement over Assets, Date of Termination rr_FeeWaiverOrReimbursementOverAssetsDateOfTermination February 1, 2023
Portfolio Turnover [Heading] rr_PortfolioTurnoverHeading Portfolio Turnover.
Portfolio Turnover [Text Block] rr_PortfolioTurnoverTextBlock

The Fund pays transaction costs, such as commissions, when it buys and sells securities (or “turns over”) its portfolio. A higher portfolio turnover rate may indicate higher transaction costs and may result in higher taxes when Fund shares are held in a taxable account. These costs, which are not reflected in Annual Fund Operating Expenses or in the Example, affect the Fund’s performance. During the most recent fiscal year, the Fund’s portfolio turnover rate was 18.99% of the average value of its portfolio.
Portfolio Turnover, Rate rr_PortfolioTurnoverRate 18.99%
Expense Example [Heading] rr_ExpenseExampleHeading Example.
Expense Example Narrative [Text Block] rr_ExpenseExampleNarrativeTextBlock

This Example is intended to help you compare the cost of investing in the Fund with the cost of investing in other mutual funds.

The Example assumes that you invest $10,000 in the Fund for the time periods indicated and then redeem all of your shares at the end of those periods. The Example also assumes that your investment has a 5% return each year, dividends and distributions are reinvested, and that the Fund’s operating expenses remain the same. Although your actual costs may be higher or lower, based on these assumptions (and giving effect to fee waivers and expense reimbursements in the first year), your costs would be:
Strategy [Heading] rr_StrategyHeading Principal Investment Strategies
Strategy Narrative [Text Block] rr_StrategyNarrativeTextBlock

The Fund pursues its investment goals by investing in a broad range of income producing securities, primarily including stocks and bonds, as described below. The Fund will under normal conditions invest at least 80% of its assets in income-producing securities, and at least 50% of its assets in common stocks.

The Fund may invest in any stock or other equity security which the investment advisor believes may assist the Fund in pursuing its investment goals (including smaller companies with market capitalization of less than $500 million and companies in developing countries), including preferred stock and publicly traded real estate investment trusts. The Fund expects that equity investments in the Fund’s portfolio normally will be weighted in favor of companies which pay dividends or other current income.

The Fund may invest in debt obligations of any kind, including corporate bonds and other obligations, mortgage- and other asset-backed securities and government obligations. The Fund may purchase debt obligations of any maturity and of any credit quality, including “high yield” or “junk” bonds. There is no minimum credit quality or rating of debt obligation the Fund may purchase. The Fund also may invest in debt obligations which have a combination of equity and debt characteristics, such as convertible bonds.

The Fund may invest a significant portion of its assets in securities of issuers domiciled in or economically tied to countries outside the United States, including developing countries.

The Fund’s investments are determined by individual issuer and industry analysis. Investment decisions are based on domestic and international economic developments, outlooks for securities markets, interest rates and inflation, the supply and demand for debt and equity securities, and analysis of specific issuers. The Fund ordinarily acquires and holds debt obligations for investment rather than for realization of gains by short-term trading on market fluctuations. However, the Fund

may dispose of any such security prior to its scheduled maturity to enhance income or reduce loss, to change the portfolio’s average maturity, or otherwise to respond to market conditions.

The Fund may sell an investment if Thornburg has identified a better investment opportunity, in response to changes in the conditions or business of the investment’s issuer or changes in overall market conditions, if Thornburg has a target price for the investment and that target price has been achieved, or if, in Thornburg’s opinion, the investment no longer serves to achieve the Fund’s investment goals.
Risk [Heading] rr_RiskHeading Principal Investment Risks
Risk Narrative [Text Block] rr_RiskNarrativeTextBlock

An investment in the Fund is not a deposit in any bank and is not insured or guaranteed by the Federal Deposit Insurance Corporation or any other government agency. Accordingly, the loss of money is a risk of investing in the Fund. The value of the Fund’s shares varies from day to day and over time, and when you sell your shares they may be worth less than what you paid for them. The following is a summary of the principal risks of investing in the Fund.

Management Risk – The Fund is an actively managed portfolio, and the value of the Fund may be reduced if Thornburg pursues unsuccessful investments or fails to correctly identify risks affecting the broad economy or specific issuers in which the Fund invests.

Market and Economic Risk – The value of the Fund’s investments may decline and its share value may be reduced due to changes in general economic and market conditions. The value of a security may change in response to developments affecting entire economies, markets or industries, including changes in interest rates, political and legal developments, and general market volatility.

Equity Risk – The value of the Fund’s equity investments may fluctuate significantly over time in response to factors affecting individual issuers, particular industries, or the market as a whole. Additionally, common stock ranks below preferred stock and debt securities in claims for dividends and for assets of a company in a liquidation or bankruptcy.

Risks Affecting Specific Issuers – The value of an equity security or debt obligation may decline in response to developments affecting the specific issuer of the security or obligation, even if the overall industry or economy is unaffected. These developments may include a variety of factors, including but not limited to management issues or other corporate disruption, a decline in revenues or profitability, an increase in costs, or an adverse effect on the issuer’s competitive position.

Small and Mid-Cap Company Risk – Investments in small-capitalization companies and mid-capitalization companies may involve additional risks, which may be relatively higher with smaller companies. These additional risks may result from limited product lines, more limited access to markets and financial resources, greater vulnerability to competition and changes in markets, lack of management depth, increased volatility in share price, and possible difficulties in valuing or selling these investments.

Credit Risk – If debt obligations held by the Fund are downgraded by ratings agencies or go into default, or if management action, legislation or other government action reduces the ability of issuers to pay principal and interest when due, the value of those obligations may decline and the Fund’s share value and the dividends paid by the Fund may be reduced. Because the ability of an issuer of a lower-rated or unrated obligation to pay principal and interest when due is typically less certain than for an issuer of a higher-rated obligation, lower-rated and unrated obligations are generally more vulnerable than higher-rated obligations to default, to ratings downgrades, and to liquidity risk. The inability of an issuer to pay principal and interest on its debt obligations when due, or the downgrading of an issuer’s debt obligations by ratings agencies, may adversely affect the market’s perceptions of the issuer’s financial strength and may therefore result in declines in the issuer’s stock price.

High Yield Risk – Debt obligations that are rated below investment grade and unrated obligations of similar credit quality (commonly referred to as “junk” or “high yield” bonds) may have a substantial risk of loss. These obligations are generally considered to be speculative with respect to the issuer’s ability to pay interest and principal when due. These obligations may be subject to greater price volatility than investment grade obligations, and their prices may decline significantly in periods of general economic difficulty or in response to adverse publicity, changes in investor perceptions or other factors. These obligations may also be subject to greater liquidity risk.

Interest Rate Risk – When interest rates increase, the value of the Fund’s investments in debt obligations may decline and the Fund’s share value may be reduced. This effect is typically more pronounced for intermediate and longer-term obligations. This effect is also typically more pronounced for mortgage- and other asset-backed securities, the value of which may fluctuate more significantly in response to interest rate changes. When interest rates decrease, the Fund’s dividends may decline.

Prepayment and Extension Risk – When market interest rates decline, certain debt obligations held by the Fund may be repaid more quickly than anticipated, requiring the Fund to reinvest the proceeds of those repayments in obligations which bear a lower interest rate. Conversely, when market interest rates increase, certain debt obligations held by the Fund may be repaid more slowly than anticipated, causing assets of the Fund to remain invested in relatively lower yielding obligations. These risks may be more pronounced for the Fund’s investments in mortgage-backed and asset-backed securities.

Foreign Investment Risk – Investments in securities of foreign issuers may involve risks including adverse fluctuations in currency exchange rates, political instability, confiscations, taxes or restrictions on currency exchange, difficulty in selling foreign investments, and reduced legal protection. In addition, some foreign government debt obligations may be subject to default, delays in payment, adverse legislation or government action, or could be downgraded by ratings agencies.

Developing Country Risk – The risks which may affect investments in foreign issuers (see “Foreign Investment Risk,” above) may be more pronounced for investments in developing countries because the economies of those countries are usually less diversified, communications, transportation and economic infrastructures are less developed, and developing countries ordinarily have less established legal, political, business and social frameworks. At times the prices of equity securities or debt obligations of a developing country issuer may be extremely volatile. An issuer domiciled in a developed country may be similarly affected by these developing country risks to the extent that the issuer conducts its business in developing countries.

Foreign Currency Risk – Fluctuations in currency exchange rates can adversely affect the value of the Fund’s foreign investments. Such fluctuations may occur for a number of reasons, including market and economic conditions, or a government’s decision to devalue its currency or impose currency controls.

Risks Affecting Specific Countries or Regions – If a significant portion of the Fund’s assets is invested in issuers that are economically exposed to one country or region, the Fund’s share value may be more susceptible to the conditions and developments in that country or region, and potentially more volatile than the share value of a more geographically diversified fund. A specific country or region could also be adversely affected by conditions or developments arising in other countries. For example, the U.S. government could take actions to prohibit or restrict individuals or companies within the U.S. from purchasing or holding the shares of issuers in another country, which may limit the Fund’s ability to invest in that country or cause the Fund to have to sell investments in that country at less than desired prices. The nature and degree of the risks affecting a given country or region, and the extent of the Fund’s exposure to any such country or region, is expected to vary over time.

Liquidity Risk – Due to a lack of demand in the marketplace or other factors, the Fund may not be able to sell some or all of its investments promptly, or may only be able to sell investments at less than desired prices.

Real Estate Risk – The Fund’s investments in publicly traded real estate investment trusts (“REITs”) are subject to risks affecting real estate investments generally (including market conditions, competition, property obsolescence, changes in interest rates and casualty to real estate), as well as risks specifically affecting REITs (the quality and skill of REIT management and the internal expenses of the REIT).

Cybersecurity and Operational Risk – Operational failures, cyber-attacks or other disruptions that affect the Fund’s service providers, the Fund’s counterparties, other market participants or the issuers of securities held by the Fund may adversely affect the Fund and its shareholders, including by causing losses for the Fund or impairing Fund operations.

Additional information about Fund investments, investment strategies and risks of investing in the Fund appears below beginning on page 61 of the Prospectus.
Risk Lose Money [Text] rr_RiskLoseMoney Accordingly, the loss of money is a risk of investing in the Fund.
RIsk Not Insured [Text] rr_RiskNotInsured An investment in the Fund is not a deposit in any bank and is not insured or guaranteed by the Federal Deposit Insurance Corporation or any other government agency.
Bar Chart and Performance Table [Heading] rr_BarChartAndPerformanceTableHeading Past Performance of the Fund
Performance Narrative [Text Block] rr_PerformanceNarrativeTextBlock

The following information provides some indication of the risks of investing in Income Builder Fund by showing how the Fund’s investment results vary from year to year. The bar chart shows how the annual total returns for Class R3 shares vary in each full year shown. The average annual total return figures compare Class R3, Class R4, Class R5 and Class R6 share performance to a Blended Benchmark, comprised of 25% Bloomberg Barclays US Aggregate Bond Total Return Value USD, which represents a broad measure of bond market performance, and 75% MSCI World Net Total Return USD Index, which represents a broad measure of equity market performance in developed markets. Past performance (before and after taxes) is not necessarily an indication of how the Fund will perform in the future. The performance information shown below is as of the calendar year ended December 31, 2021. Updated performance information may be obtained on the Thornburg website at www.thornburg.com or by calling 1-800-847-0200.
Performance Information Illustrates Variability of Returns [Text] rr_PerformanceInformationIllustratesVariabilityOfReturns The following information provides some indication of the risks of investing in Income Builder Fund by showing how the Fund’s investment results vary from year to year.
Performance Availability Phone [Text] rr_PerformanceAvailabilityPhone 1-800-847-0200
Performance Availability Website Address [Text] rr_PerformanceAvailabilityWebSiteAddress www.thornburg.com
Performance Past Does Not Indicate Future [Text] rr_PerformancePastDoesNotIndicateFuture Past performance (before and after taxes) is not necessarily an indication of how the Fund will perform in the future.
Bar Chart [Heading] rr_BarChartHeading Annual Total Returns – Class R3 Shares
Bar Chart Closing [Text Block] rr_BarChartClosingTextBlock

Total
Returns

Quarter
ended

Highest Quarterly Results

15.81%

12/31/2020

Lowest Quarterly Results

(26.02)%

3/31/2020
Performance Table Heading rr_PerformanceTableHeading Average Annual Total Returns (periods ended 12-31-21)
Performance Table Uses Highest Federal Rate rr_PerformanceTableUsesHighestFederalRate After-tax returns are calculated using the highest historical individual federal marginal income tax rates, and do not reflect state or local income taxes.
Performance Table Not Relevant to Tax Deferred rr_PerformanceTableNotRelevantToTaxDeferred Actual after-tax returns depend on an investor’s own tax situation and may differ from the returns shown, and after-tax returns shown are not relevant to investors who hold their Fund shares through tax-deferred arrangements, such as 401(k) plans or individual retirement accounts.
Performance Table One Class of after Tax Shown [Text] rr_PerformanceTableOneClassOfAfterTaxShown The after-tax returns shown relate only to Class R3 shares, and after-tax returns for other share classes will vary.
Performance Table Closing [Text Block] rr_PerformanceTableClosingTextBlock

After-tax returns are calculated using the highest historical individual federal marginal income tax rates, and do not reflect state or local income taxes. Actual after-tax returns depend on an investor’s own tax situation and may differ from the returns shown, and after-tax returns shown are not relevant to investors who hold their Fund shares through tax-deferred arrangements, such as 401(k) plans or individual retirement accounts. The after-tax returns shown relate only to Class R3 shares, and after-tax returns for other share classes will vary.
Retirement | Thornburg Investment Income Builder Fund | Thornburg Investment Income Builder Fund - Class R3  
Prospectus [Line Items] rr_ProspectusLineItems  
Trading Symbol dei_TradingSymbol TIBRX
Maximum Sales Charge Imposed on Purchases (as a percentage of Offering Price) rr_MaximumSalesChargeImposedOnPurchasesOverOfferingPrice none
Maximum Deferred Sales Charge (as a percentage) rr_MaximumDeferredSalesChargeOverOther none
Management Fees (as a percentage of Assets) rr_ManagementFeesOverAssets 0.70%
Distribution and Service (12b-1) Fees rr_DistributionAndService12b1FeesOverAssets 0.50%
Other Expenses (as a percentage of Assets): rr_OtherExpensesOverAssets 0.38% [69]
Acquired Fund Fees and Expenses rr_AcquiredFundFeesAndExpensesOverAssets 0.05%
Expenses (as a percentage of Assets) rr_ExpensesOverAssets 1.63%
Fee Waiver or Reimbursement rr_FeeWaiverOrReimbursementOverAssets (0.08%) [70]
Net Expenses (as a percentage of Assets) rr_NetExpensesOverAssets 1.55% [71]
Expense Example, with Redemption, 1 Year rr_ExpenseExampleYear01 $ 158
Expense Example, with Redemption, 3 Years rr_ExpenseExampleYear03 506
Expense Example, with Redemption, 5 Years rr_ExpenseExampleYear05 879
Expense Example, with Redemption, 10 Years rr_ExpenseExampleYear10 $ 1,926
Annual Return 2012 rr_AnnualReturn2012 11.11%
Annual Return 2013 rr_AnnualReturn2013 16.09%
Annual Return 2014 rr_AnnualReturn2014 4.28%
Annual Return 2015 rr_AnnualReturn2015 (5.72%)
Annual Return 2016 rr_AnnualReturn2016 9.17%
Annual Return 2017 rr_AnnualReturn2017 14.49%
Annual Return 2018 rr_AnnualReturn2018 (5.01%)
Annual Return 2019 rr_AnnualReturn2019 17.28%
Annual Return 2020 rr_AnnualReturn2020 (1.02%)
Annual Return 2021 rr_AnnualReturn2021 19.59%
Highest Quarterly Return, Label rr_HighestQuarterlyReturnLabel Highest Quarterly Results
Highest Quarterly Return, Date rr_BarChartHighestQuarterlyReturnDate Dec. 31, 2020
Highest Quarterly Return rr_BarChartHighestQuarterlyReturn 15.81%
Lowest Quarterly Return, Label rr_LowestQuarterlyReturnLabel Lowest Quarterly Results
Lowest Quarterly Return, Date rr_BarChartLowestQuarterlyReturnDate Mar. 31, 2020
Lowest Quarterly Return rr_BarChartLowestQuarterlyReturn (26.02%)
1 Year rr_AverageAnnualReturnYear01 19.59%
5 Years rr_AverageAnnualReturnYear05 8.59%
10 Years rr_AverageAnnualReturnYear10 7.65%
Retirement | Thornburg Investment Income Builder Fund | Thornburg Investment Income Builder Fund - Class R3 | After Taxes on Distributions  
Prospectus [Line Items] rr_ProspectusLineItems  
1 Year rr_AverageAnnualReturnYear01 17.25%
5 Years rr_AverageAnnualReturnYear05 6.72%
10 Years rr_AverageAnnualReturnYear10 5.77%
Retirement | Thornburg Investment Income Builder Fund | Thornburg Investment Income Builder Fund - Class R3 | After Taxes on Distributions and Sales  
Prospectus [Line Items] rr_ProspectusLineItems  
1 Year rr_AverageAnnualReturnYear01 11.53%
5 Years rr_AverageAnnualReturnYear05 5.81%
10 Years rr_AverageAnnualReturnYear10 5.14%
Retirement | Thornburg Investment Income Builder Fund | Thornburg Investment Income Builder Fund - Class R3 | Blended Index (reflects no deduction for fees, expenses, or U.S. taxes)  
Prospectus [Line Items] rr_ProspectusLineItems  
1 Year rr_AverageAnnualReturnYear01 15.64%
5 Years rr_AverageAnnualReturnYear05 12.30%
10 Years rr_AverageAnnualReturnYear10 10.36%
Retirement | Thornburg Investment Income Builder Fund | Thornburg Investment Income Builder Fund - Class R4  
Prospectus [Line Items] rr_ProspectusLineItems  
Trading Symbol dei_TradingSymbol TIBGX
Maximum Sales Charge Imposed on Purchases (as a percentage of Offering Price) rr_MaximumSalesChargeImposedOnPurchasesOverOfferingPrice none
Maximum Deferred Sales Charge (as a percentage) rr_MaximumDeferredSalesChargeOverOther none
Management Fees (as a percentage of Assets) rr_ManagementFeesOverAssets 0.70%
Distribution and Service (12b-1) Fees rr_DistributionAndService12b1FeesOverAssets 0.25%
Other Expenses (as a percentage of Assets): rr_OtherExpensesOverAssets 0.51% [69]
Acquired Fund Fees and Expenses rr_AcquiredFundFeesAndExpensesOverAssets 0.05%
Expenses (as a percentage of Assets) rr_ExpensesOverAssets 1.51%
Fee Waiver or Reimbursement rr_FeeWaiverOrReimbursementOverAssets (0.06%) [70]
Net Expenses (as a percentage of Assets) rr_NetExpensesOverAssets 1.45% [71]
Expense Example, with Redemption, 1 Year rr_ExpenseExampleYear01 $ 148
Expense Example, with Redemption, 3 Years rr_ExpenseExampleYear03 471
Expense Example, with Redemption, 5 Years rr_ExpenseExampleYear05 818
Expense Example, with Redemption, 10 Years rr_ExpenseExampleYear10 $ 1,796
1 Year rr_AverageAnnualReturnYear01 19.69%
5 Years rr_AverageAnnualReturnYear05 8.69%
10 Years rr_AverageAnnualReturnYear10 7.75%
Retirement | Thornburg Investment Income Builder Fund | Thornburg Investment Income Builder Fund - Class R4 | Blended Index (reflects no deduction for fees, expenses, or U.S. taxes)  
Prospectus [Line Items] rr_ProspectusLineItems  
1 Year rr_AverageAnnualReturnYear01 15.64%
5 Years rr_AverageAnnualReturnYear05 12.30%
10 Years rr_AverageAnnualReturnYear10 10.36%
Retirement | Thornburg Investment Income Builder Fund | Thornburg Investment Income Builder Fund - Class R5  
Prospectus [Line Items] rr_ProspectusLineItems  
Trading Symbol dei_TradingSymbol TIBMX
Maximum Sales Charge Imposed on Purchases (as a percentage of Offering Price) rr_MaximumSalesChargeImposedOnPurchasesOverOfferingPrice none
Maximum Deferred Sales Charge (as a percentage) rr_MaximumDeferredSalesChargeOverOther none
Management Fees (as a percentage of Assets) rr_ManagementFeesOverAssets 0.70%
Distribution and Service (12b-1) Fees rr_DistributionAndService12b1FeesOverAssets none
Other Expenses (as a percentage of Assets): rr_OtherExpensesOverAssets 0.39% [69]
Acquired Fund Fees and Expenses rr_AcquiredFundFeesAndExpensesOverAssets 0.05%
Expenses (as a percentage of Assets) rr_ExpensesOverAssets 1.14%
Fee Waiver or Reimbursement rr_FeeWaiverOrReimbursementOverAssets (0.10%) [70]
Net Expenses (as a percentage of Assets) rr_NetExpensesOverAssets 1.04% [71]
Expense Example, with Redemption, 1 Year rr_ExpenseExampleYear01 $ 106
Expense Example, with Redemption, 3 Years rr_ExpenseExampleYear03 352
Expense Example, with Redemption, 5 Years rr_ExpenseExampleYear05 618
Expense Example, with Redemption, 10 Years rr_ExpenseExampleYear10 $ 1,377
1 Year rr_AverageAnnualReturnYear01 20.18%
5 Years rr_AverageAnnualReturnYear05 9.13%
10 Years rr_AverageAnnualReturnYear10 8.19%
Retirement | Thornburg Investment Income Builder Fund | Thornburg Investment Income Builder Fund - Class R5 | Blended Index (reflects no deduction for fees, expenses, or U.S. taxes)  
Prospectus [Line Items] rr_ProspectusLineItems  
1 Year rr_AverageAnnualReturnYear01 15.64%
5 Years rr_AverageAnnualReturnYear05 12.30%
10 Years rr_AverageAnnualReturnYear10 10.36%
Retirement | Thornburg Investment Income Builder Fund | Thornburg Investment Income Builder Fund - Class R6  
Prospectus [Line Items] rr_ProspectusLineItems  
Trading Symbol dei_TradingSymbol TIBOX
Maximum Sales Charge Imposed on Purchases (as a percentage of Offering Price) rr_MaximumSalesChargeImposedOnPurchasesOverOfferingPrice none
Maximum Deferred Sales Charge (as a percentage) rr_MaximumDeferredSalesChargeOverOther none
Management Fees (as a percentage of Assets) rr_ManagementFeesOverAssets 0.70%
Distribution and Service (12b-1) Fees rr_DistributionAndService12b1FeesOverAssets none
Other Expenses (as a percentage of Assets): rr_OtherExpensesOverAssets 0.14% [69]
Acquired Fund Fees and Expenses rr_AcquiredFundFeesAndExpensesOverAssets 0.05%
Expenses (as a percentage of Assets) rr_ExpensesOverAssets 0.89%
Fee Waiver or Reimbursement rr_FeeWaiverOrReimbursementOverAssets (0.04%) [70]
Net Expenses (as a percentage of Assets) rr_NetExpensesOverAssets 0.85% [71]
Expense Example, with Redemption, 1 Year rr_ExpenseExampleYear01 $ 87
Expense Example, with Redemption, 3 Years rr_ExpenseExampleYear03 280
Expense Example, with Redemption, 5 Years rr_ExpenseExampleYear05 489
Expense Example, with Redemption, 10 Years rr_ExpenseExampleYear10 $ 1,092
1 Year rr_AverageAnnualReturnYear01 20.38%
Since Inception rr_AverageAnnualReturnSinceInception 9.12%
Inception Date rr_AverageAnnualReturnInceptionDate Apr. 10, 2017
Retirement | Thornburg Investment Income Builder Fund | Thornburg Investment Income Builder Fund - Class R6 | Blended Index (reflects no deduction for fees, expenses, or U.S. taxes)  
Prospectus [Line Items] rr_ProspectusLineItems  
1 Year rr_AverageAnnualReturnYear01 15.64%
Since Inception rr_AverageAnnualReturnSinceInception 11.95%
Retirement | Thornburg Limited Term U.S. Government Fund  
Prospectus [Line Items] rr_ProspectusLineItems  
Risk/Return [Heading] rr_RiskReturnHeading Limited Term U.S. Government Fund
Objective [Heading] rr_ObjectiveHeading Investment Goal
Objective, Primary [Text Block] rr_ObjectivePrimaryTextBlock

The primary goal of Limited Term U.S. Government Fund is to provide as high a level of current income as is consistent, in the view of the Fund’s investment advisor, with safety of capital.
Objective, Secondary [Text Block] rr_ObjectiveSecondaryTextBlock

As a secondary goal, the Fund seeks to reduce changes in its share price compared to longer term portfolios.
Expense [Heading] rr_ExpenseHeading Fees and Expenses of the Fund
Expense Narrative [Text Block] rr_ExpenseNarrativeTextBlock

This table describes the fees and expenses that you may pay if you buy and hold shares of the Fund.
Shareholder Fees Caption [Text] rr_ShareholderFeesCaption Shareholder Fees (fees paid directly from your investment)
Operating Expenses Caption [Text] rr_OperatingExpensesCaption Annual Fund Operating Expenses (expenses that you pay each year as a percentage of the value of your investment)
Fee Waiver or Reimbursement over Assets, Date of Termination rr_FeeWaiverOrReimbursementOverAssetsDateOfTermination February 1, 2023
Portfolio Turnover [Heading] rr_PortfolioTurnoverHeading Portfolio Turnover.
Portfolio Turnover [Text Block] rr_PortfolioTurnoverTextBlock

The Fund pays transaction costs, such as commissions, when it buys and sells securities (or “turns over”) its portfolio. A higher portfolio turnover rate may indicate higher transaction costs and may result in higher taxes when Fund shares are held in a taxable account. These costs, which are not reflected in Annual Fund Operating Expenses or in the Example, affect the Fund’s performance. During the most recent fiscal year, the Fund’s portfolio turnover rate was 9.50% of the average value of its portfolio.
Portfolio Turnover, Rate rr_PortfolioTurnoverRate 9.50%
Expense Example [Heading] rr_ExpenseExampleHeading Example.
Expense Example Narrative [Text Block] rr_ExpenseExampleNarrativeTextBlock

This Example is intended to help you compare the cost of investing in the Fund with the cost of investing in other mutual funds.

The Example assumes that you invest $10,000 in the Fund for the time periods indicated and then redeem all of your shares at the end of those periods. The Example also assumes that your investment has a 5% return each year, dividends and distributions are reinvested, and that the Fund’s operating expenses remain the same. Although your actual costs may be higher or lower, based on these assumptions (and giving effect to fee waivers and expense reimbursements in the first year), your costs would be:
Strategy [Heading] rr_StrategyHeading Principal Investment Strategies
Strategy Narrative [Text Block] rr_StrategyNarrativeTextBlock

Thornburg Investment Management, Inc. (“Thornburg”) actively manages the Fund’s portfolio in pursuing the Fund’s investment goals. While Thornburg follows domestic and international economic developments, outlooks for securities markets, interest rates and inflation, the supply and demand for debt obligations, and other factors, the Fund’s investments are determined by individual security analysis. The Fund ordinarily acquires and holds securities for investment rather than for realization of gains by short-term trading on market fluctuations. However, it may dispose of any security before its scheduled maturity to enhance income or reduce loss, to change the portfolio’s average maturity, or to otherwise respond to market conditions.

Limited Term U.S. Government Fund invests at least 80% of its assets in U.S. Government Securities. For this purpose, “U.S. Government Securities” means:

Securities backed by the full faith and credit of the U.S. government, including direct obligations of the U.S. Treasury (such as U.S. Treasury Bonds) and obligations of U.S. government agencies and instrumentalities which are guaranteed by the U.S. Treasury (such as “Ginnie Mae” mortgage-backed certificates issued by the Government National Mortgage Association).

Securities issued or guaranteed by U.S. government agencies, instrumentalities or sponsored enterprises, but which are not backed by the full faith and credit of the U.S. government. These securities include mortgage-backed certificates, collateralized mortgage obligations (“CMOs”), and debentures issued by “Freddie Mac” (Federal Home Loan Mortgage Corporation) and “Fannie Mae” (Federal National Mortgage Association).

U.S. Government Securities include for this purpose repurchase agreements secured by the securities described above, and participations having economic characteristics similar to those securities. “Participations” are undivided interests in pools of securities where the underlying credit support passes through to the participants.

Because the magnitude of changes in the value of interest-bearing obligations is greater for obligations with longer terms given an equivalent change in interest rates, the Fund seeks to reduce changes in its share value by maintaining a portfolio of investments with a dollar-weighted average maturity or expected life of normally less than five years. There is no limitation on the maturity of any specific security the Fund may purchase, and the Fund may sell any security before it matures. The Fund also attempts to reduce changes in share value through credit analysis, selection and diversification.

The Fund ordinarily acquires and holds securities for investment rather than for realization of gains by short-term trading on market fluctuations. However, it may sell an investment prior to its scheduled maturity date to enhance income or reduce loss, to change the portfolio’s average duration or average maturity, to pursue other investment opportunities, in response to changes in the conditions or business of the investment’s issuer or changes in overall market conditions, or if, in Thornburg’s opinion, the investment no longer serves to achieve the Fund’s investment goals. The objective of preserving capital may prevent the Fund from obtaining the highest yields available.
Risk [Heading] rr_RiskHeading Principal Investment Risks
Risk Narrative [Text Block] rr_RiskNarrativeTextBlock

Although the Fund may acquire obligations issued or guaranteed by the U.S. government and its agencies, instrumentalities and enterprises, neither the Fund’s net asset value nor its dividends are guaranteed by the U.S. government. An investment in the Fund is not a deposit in any bank and is not insured or guaranteed by the Federal Deposit Insurance Corporation or any other government agency. Accordingly, the loss of money is a risk of investing in the Fund. The value of the Fund’s shares and its dividends may fluctuate from day to day and over time, and when you sell your shares they may be worth less than what you paid for them. If your sole objective is preservation of capital, then the Fund may not be suitable for you because the Fund’s share value will fluctuate, including as interest rates change. Investors whose sole objective is preservation of capital may wish to consider a high quality money market fund. The following is a summary of the principal risks of investing in the Fund.

Management Risk – The Fund is an actively managed portfolio, and the value of the Fund may be reduced if Thornburg pursues unsuccessful investments or fails to correctly identify risks affecting the broad economy or specific issuers in which the Fund invests.

Interest Rate Risk – When interest rates increase, the value of the Fund’s investments may decline and the Fund’s share value may be reduced. This effect is typically more pronounced for intermediate and longer-term obligations. This effect is also typically more pronounced for the Fund’s investment in mortgage-backed securities, the value of which may fluctuate more significantly in response to interest rate changes. When interest rates decrease, the Fund’s dividends may decline.

Prepayment and Extension Risk – When market interest rates decline, certain debt obligations held by the Fund may be repaid more quickly than anticipated, requiring the Fund to reinvest the proceeds of those repayments in obligations which bear a lower interest rate. Conversely, when market interest rates increase, certain debt obligations held by the Fund may be repaid more slowly than anticipated, causing assets of the Fund to remain invested in relatively lower yielding obligations. These risks may be more pronounced for the Fund’s investments in mortgage-backed securities.

Credit Risk – All securities owned by the Fund may be subject to default, delays in payment, adverse legislation or other government action, or could be downgraded by ratings agencies, reducing the value of the Fund’s shares. Securities backed by the full faith and credit of the U.S. government, such as U.S. Treasury obligations, are commonly regarded as having small exposure to credit risk. Obligations of certain U.S. government agencies, instrumentalities and government-sponsored enterprises (sometimes referred to as “agency obligations”) are not direct obligations of the United States, may not be backed by the full faith and credit of the U.S. government, and may have a greater exposure to credit risk. Although the U.S. government is required by law to provide credit support for some agency obligations, there is no assurance that the U.S. government would provide financial support for any such obligation on a default by the issuing agency, instrumentality or enterprise in the absence of a legal requirement to do so. As of the date of this Prospectus, securities backed by the full faith and credit of the U.S. government, and securities of U.S. government agencies, instrumentalities and enterprises which may be purchased by the Fund are rated “Aaa” by Moody’s Investors Services or “AA+” by S&P Global Ratings. Ratings agencies may reduce the ratings of any securities in the future.

Market and Economic Risk – The value of the Fund’s investments may decline and its share value may be reduced due to changes in general economic and market conditions. For example, a fall in worldwide demand for U.S. government securities or general economic decline could lower the value of those securities.

Liquidity Risk – Due to a lack of demand in the marketplace or other factors, the Fund may not be able to sell promptly some or all of the obligations that it holds, or may only be able to sell obligations at less than desired prices.

Structured Products Risk – Investments in securities that are backed by, or represent interests in, an underlying pool of securities or other assets, including investments in mortgage- and asset-backed securities and in collateralized mortgage obligations and collateralized debt obligations, involve the risks associated with the underlying assets (e.g., the risk of default by mortgagors whose mortgages are included in a mortgage-backed security or collateralized mortgage obligation), and may also involve different or greater risks, including the risk that distributions from the underlying assets will be inadequate to make interest or other payments to the Fund, the risk that the issuer of the securities will fail to administer the underlying assets properly or become insolvent, and the risk that the securities will be less liquid than other Fund investments.

Cybersecurity and Operational Risk – Operational failures, cyber-attacks or other disruptions that affect the Fund’s service providers, the Fund’s counterparties, other market participants or the issuers of securities held by the Fund may adversely affect the Fund and its shareholders, including by causing losses for the Fund or impairing Fund operations.

Additional information about Fund investments, investment strategies, and risks of investing in the Fund appears beginning on page 61 of the Prospectus.
Risk Lose Money [Text] rr_RiskLoseMoney Accordingly, the loss of money is a risk of investing in the Fund.
RIsk Not Insured [Text] rr_RiskNotInsured An investment in the Fund is not a deposit in any bank and is not insured or guaranteed by the Federal Deposit Insurance Corporation or any other government agency.
Bar Chart and Performance Table [Heading] rr_BarChartAndPerformanceTableHeading Past Performance of the Fund
Performance Narrative [Text Block] rr_PerformanceNarrativeTextBlock

The following information provides some indication of the risks of investing in Limited Term U.S. Government Fund by showing how the Fund’s investment results vary from year to year. The bar chart shows how the annual total returns for Class R3 shares have been different in each full year shown. The average annual total return figures compare Class R3, Class R4, and Class R5 share performance to the Bloomberg Barclays US Government Intermediate Total Return Index Value Unhedged, a broad measure of market performance. Past performance (before and after taxes) is not necessarily an indication of how the Fund will perform in the future. The performance information shown below is as of the calendar year ended December 31, 2021. Updated performance information may be obtained on the Thornburg website at www.thornburg.com or by calling 1-800-847-0200.
Performance Information Illustrates Variability of Returns [Text] rr_PerformanceInformationIllustratesVariabilityOfReturns The following information provides some indication of the risks of investing in Limited Term U.S. Government Fund by showing how the Fund’s investment results vary from year to year.
Performance Availability Phone [Text] rr_PerformanceAvailabilityPhone 1-800-847-0200
Performance Availability Website Address [Text] rr_PerformanceAvailabilityWebSiteAddress www.thornburg.com
Performance Past Does Not Indicate Future [Text] rr_PerformancePastDoesNotIndicateFuture Past performance (before and after taxes) is not necessarily an indication of how the Fund will perform in the future.
Bar Chart [Heading] rr_BarChartHeading Annual Total Returns – Class R3 Shares
Bar Chart Closing [Text Block] rr_BarChartClosingTextBlock

Total
Returns

Quarter
ended

Highest Quarterly Results

1.84%

3/31/2020

Lowest Quarterly Results

(1.71)%

3/31/2021
Performance Table Heading rr_PerformanceTableHeading Average Annual Total Returns (periods ended 12-31-21)
Performance Table Uses Highest Federal Rate rr_PerformanceTableUsesHighestFederalRate After-tax returns are calculated using the highest historical individual federal marginal income tax rates, and do not reflect state or local income taxes.
Performance Table Not Relevant to Tax Deferred rr_PerformanceTableNotRelevantToTaxDeferred Actual after-tax returns depend on an investor’s own tax situation and may differ from the returns shown, and after-tax returns shown are not relevant to investors who hold their Fund shares through tax-deferred arrangements, such as 401(k) plans or individual retirement accounts.
Performance Table One Class of after Tax Shown [Text] rr_PerformanceTableOneClassOfAfterTaxShown The after-tax returns shown relate only to Class R3 shares, and after-tax returns for other share classes will vary.
Performance Table Closing [Text Block] rr_PerformanceTableClosingTextBlock

After-tax returns are calculated using the highest historical individual federal marginal income tax rates, and do not reflect state or local income taxes. Actual after-tax returns depend on an investor’s own tax situation and may differ from the returns shown, and after-tax returns shown are not relevant to investors who hold their Fund shares through tax-deferred arrangements, such as 401(k) plans or individual retirement accounts. The after-tax returns shown relate only to Class R3 shares, and after-tax returns for other share classes will vary.
Retirement | Thornburg Limited Term U.S. Government Fund | Thornburg Limited Term U.S. Government Fund - Class R3  
Prospectus [Line Items] rr_ProspectusLineItems  
Trading Symbol dei_TradingSymbol LTURX
Maximum Sales Charge Imposed on Purchases (as a percentage of Offering Price) rr_MaximumSalesChargeImposedOnPurchasesOverOfferingPrice none
Maximum Deferred Sales Charge (as a percentage) rr_MaximumDeferredSalesChargeOverOther none
Management Fees (as a percentage of Assets) rr_ManagementFeesOverAssets 0.37%
Distribution and Service (12b-1) Fees rr_DistributionAndService12b1FeesOverAssets 0.50%
Other Expenses (as a percentage of Assets): rr_OtherExpensesOverAssets 0.44%
Expenses (as a percentage of Assets) rr_ExpensesOverAssets 1.31%
Fee Waiver or Reimbursement rr_FeeWaiverOrReimbursementOverAssets (0.32%) [72]
Net Expenses (as a percentage of Assets) rr_NetExpensesOverAssets 0.99%
Expense Example, with Redemption, 1 Year rr_ExpenseExampleYear01 $ 101
Expense Example, with Redemption, 3 Years rr_ExpenseExampleYear03 384
Expense Example, with Redemption, 5 Years rr_ExpenseExampleYear05 688
Expense Example, with Redemption, 10 Years rr_ExpenseExampleYear10 $ 1,551
Annual Return 2012 rr_AnnualReturn2012 1.91%
Annual Return 2013 rr_AnnualReturn2013 (1.96%)
Annual Return 2014 rr_AnnualReturn2014 2.19%
Annual Return 2015 rr_AnnualReturn2015 0.27%
Annual Return 2016 rr_AnnualReturn2016 0.91%
Annual Return 2017 rr_AnnualReturn2017 0.56%
Annual Return 2018 rr_AnnualReturn2018 0.73%
Annual Return 2019 rr_AnnualReturn2019 3.52%
Annual Return 2020 rr_AnnualReturn2020 3.66%
Annual Return 2021 rr_AnnualReturn2021 (1.94%)
Highest Quarterly Return, Label rr_HighestQuarterlyReturnLabel Highest Quarterly Results
Highest Quarterly Return, Date rr_BarChartHighestQuarterlyReturnDate Mar. 31, 2020
Highest Quarterly Return rr_BarChartHighestQuarterlyReturn 1.84%
Lowest Quarterly Return, Label rr_LowestQuarterlyReturnLabel Lowest Quarterly Results
Lowest Quarterly Return, Date rr_BarChartLowestQuarterlyReturnDate Mar. 31, 2021
Lowest Quarterly Return rr_BarChartLowestQuarterlyReturn (1.71%)
1 Year rr_AverageAnnualReturnYear01 (1.94%)
5 Years rr_AverageAnnualReturnYear05 1.28%
10 Years rr_AverageAnnualReturnYear10 0.97%
Retirement | Thornburg Limited Term U.S. Government Fund | Thornburg Limited Term U.S. Government Fund - Class R3 | After Taxes on Distributions  
Prospectus [Line Items] rr_ProspectusLineItems  
1 Year rr_AverageAnnualReturnYear01 (2.38%)
5 Years rr_AverageAnnualReturnYear05 0.69%
10 Years rr_AverageAnnualReturnYear10 0.29%
Retirement | Thornburg Limited Term U.S. Government Fund | Thornburg Limited Term U.S. Government Fund - Class R3 | After Taxes on Distributions and Sales  
Prospectus [Line Items] rr_ProspectusLineItems  
1 Year rr_AverageAnnualReturnYear01 (1.15%)
5 Years rr_AverageAnnualReturnYear05 0.73%
10 Years rr_AverageAnnualReturnYear10 0.45%
Retirement | Thornburg Limited Term U.S. Government Fund | Thornburg Limited Term U.S. Government Fund - Class R3 | Bloomberg Barclays Intermediate Government Bond Index (reflects no deduction for fees, expenses, or taxes)  
Prospectus [Line Items] rr_ProspectusLineItems  
1 Year rr_AverageAnnualReturnYear01 (1.69%)
5 Years rr_AverageAnnualReturnYear05 2.32%
10 Years rr_AverageAnnualReturnYear10 1.68%
Retirement | Thornburg Limited Term U.S. Government Fund | Thornburg Limited Term U.S. Government Fund - Class R4  
Prospectus [Line Items] rr_ProspectusLineItems  
Trading Symbol dei_TradingSymbol LTUGX
Maximum Sales Charge Imposed on Purchases (as a percentage of Offering Price) rr_MaximumSalesChargeImposedOnPurchasesOverOfferingPrice none
Maximum Deferred Sales Charge (as a percentage) rr_MaximumDeferredSalesChargeOverOther none
Management Fees (as a percentage of Assets) rr_ManagementFeesOverAssets 0.37%
Distribution and Service (12b-1) Fees rr_DistributionAndService12b1FeesOverAssets 0.25%
Other Expenses (as a percentage of Assets): rr_OtherExpensesOverAssets 1.01%
Expenses (as a percentage of Assets) rr_ExpensesOverAssets 1.63%
Fee Waiver or Reimbursement rr_FeeWaiverOrReimbursementOverAssets (0.64%) [72]
Net Expenses (as a percentage of Assets) rr_NetExpensesOverAssets 0.99%
Expense Example, with Redemption, 1 Year rr_ExpenseExampleYear01 $ 101
Expense Example, with Redemption, 3 Years rr_ExpenseExampleYear03 452
Expense Example, with Redemption, 5 Years rr_ExpenseExampleYear05 826
Expense Example, with Redemption, 10 Years rr_ExpenseExampleYear10 $ 1,879
1 Year rr_AverageAnnualReturnYear01 (1.95%)
5 Years rr_AverageAnnualReturnYear05 1.28%
Since Inception rr_AverageAnnualReturnSinceInception 1.11%
Inception Date rr_AverageAnnualReturnInceptionDate Feb. 01, 2014
Retirement | Thornburg Limited Term U.S. Government Fund | Thornburg Limited Term U.S. Government Fund - Class R4 | Bloomberg Barclays Intermediate Government Bond Index (reflects no deduction for fees, expenses, or taxes)  
Prospectus [Line Items] rr_ProspectusLineItems  
1 Year rr_AverageAnnualReturnYear01 (1.69%)
5 Years rr_AverageAnnualReturnYear05 2.32%
Since Inception rr_AverageAnnualReturnSinceInception 1.96%
Retirement | Thornburg Limited Term U.S. Government Fund | Thornburg Limited Term U.S. Government Fund - Class R5  
Prospectus [Line Items] rr_ProspectusLineItems  
Trading Symbol dei_TradingSymbol LTGRX
Maximum Sales Charge Imposed on Purchases (as a percentage of Offering Price) rr_MaximumSalesChargeImposedOnPurchasesOverOfferingPrice none
Maximum Deferred Sales Charge (as a percentage) rr_MaximumDeferredSalesChargeOverOther none
Management Fees (as a percentage of Assets) rr_ManagementFeesOverAssets 0.37%
Distribution and Service (12b-1) Fees rr_DistributionAndService12b1FeesOverAssets none
Other Expenses (as a percentage of Assets): rr_OtherExpensesOverAssets 1.19%
Expenses (as a percentage of Assets) rr_ExpensesOverAssets 1.56%
Fee Waiver or Reimbursement rr_FeeWaiverOrReimbursementOverAssets (0.89%) [72]
Net Expenses (as a percentage of Assets) rr_NetExpensesOverAssets 0.67%
Expense Example, with Redemption, 1 Year rr_ExpenseExampleYear01 $ 68
Expense Example, with Redemption, 3 Years rr_ExpenseExampleYear03 405
Expense Example, with Redemption, 5 Years rr_ExpenseExampleYear05 766
Expense Example, with Redemption, 10 Years rr_ExpenseExampleYear10 $ 1,781
1 Year rr_AverageAnnualReturnYear01 (1.63%)
5 Years rr_AverageAnnualReturnYear05 1.62%
Since Inception rr_AverageAnnualReturnSinceInception 1.26%
Inception Date rr_AverageAnnualReturnInceptionDate May 01, 2012
Retirement | Thornburg Limited Term U.S. Government Fund | Thornburg Limited Term U.S. Government Fund - Class R5 | Bloomberg Barclays Intermediate Government Bond Index (reflects no deduction for fees, expenses, or taxes)  
Prospectus [Line Items] rr_ProspectusLineItems  
1 Year rr_AverageAnnualReturnYear01 (1.69%)
5 Years rr_AverageAnnualReturnYear05 2.32%
Since Inception rr_AverageAnnualReturnSinceInception 1.69%
Retirement | Thornburg Limited Term Income Fund  
Prospectus [Line Items] rr_ProspectusLineItems  
Risk/Return [Heading] rr_RiskReturnHeading Limited Term Income Fund
Objective [Heading] rr_ObjectiveHeading Investment Goal
Objective, Primary [Text Block] rr_ObjectivePrimaryTextBlock

The primary goal of Limited Term Income Fund is to provide as high a level of current income as is consistent, in the view of the Fund’s investment advisor, with safety of capital.
Objective, Secondary [Text Block] rr_ObjectiveSecondaryTextBlock

As a secondary goal, the Fund seeks to reduce changes in its share prices compared to longer term portfolios.
Expense [Heading] rr_ExpenseHeading Fees and Expenses of the Fund
Expense Narrative [Text Block] rr_ExpenseNarrativeTextBlock

This table describes the fees and expenses that you may pay if you buy and hold shares of the Fund.
Shareholder Fees Caption [Text] rr_ShareholderFeesCaption Shareholder Fees (fees paid directly from your investment)
Operating Expenses Caption [Text] rr_OperatingExpensesCaption Annual Fund Operating Expenses (expenses that you pay each year as a percentage of the value of your investment)
Fee Waiver or Reimbursement over Assets, Date of Termination rr_FeeWaiverOrReimbursementOverAssetsDateOfTermination February 1, 2023
Portfolio Turnover [Heading] rr_PortfolioTurnoverHeading Portfolio Turnover.
Portfolio Turnover [Text Block] rr_PortfolioTurnoverTextBlock

The Fund pays transaction costs, such as commissions, when it buys and sells securities (or “turns over”) its portfolio. A higher portfolio turnover rate may indicate higher transaction costs and may result in higher taxes when Fund shares are held in a taxable account. These costs, which are not reflected in Annual Fund Operating Expenses or in the Example, affect the Fund’s performance. During the most recent fiscal year, the Fund’s portfolio turnover rate was 33.37% of the average value of its portfolio.
Portfolio Turnover, Rate rr_PortfolioTurnoverRate 33.37%
Expense Example [Heading] rr_ExpenseExampleHeading Example.
Expense Example Narrative [Text Block] rr_ExpenseExampleNarrativeTextBlock

This Example is intended to help you compare the cost of investing in the Fund with the cost of investing in other mutual funds.

The Example assumes that you invest $10,000 in the Fund for the time periods indicated and then redeem all of your shares at the end of those periods. The Example also assumes that your investment has a 5% return each year, dividends and distributions are reinvested, and that the Fund’s operating expenses remain the same. Although your actual costs may be higher or lower, based on these assumptions (and giving effect to fee waivers and expense reimbursements in the first year), your costs would be:
Strategy [Heading] rr_StrategyHeading Principal Investment Strategies
Strategy Narrative [Text Block] rr_StrategyNarrativeTextBlock

Thornburg Investment Management, Inc. (“Thornburg”) actively manages the Fund’s portfolio in pursuing the Fund’s investment goals. While Thornburg follows domestic and international economic developments, outlooks for securities markets, interest rates and inflation, the supply and demand for debt obligations, and other factors, the Fund’s investments are determined by individual security analysis. The Fund ordinarily acquires and holds securities for investment rather than for realization of gains by short-term trading on market fluctuations. However, it may dispose of any security prior to its scheduled maturity to enhance income or reduce loss, to change the portfolio’s average maturity, or to otherwise respond to current market conditions.

The Fund invests at least 65% of its net assets in (i) obligations of the U.S. government, its agencies and instrumentalities, and (ii) debt obligations rated at the time of purchase in one of the three highest principal long term rating categories of S&P Global Ratings (AAA, AA or A) or Moody’s Investors Services, Inc. (Aaa, Aa or A), or the equivalent three highest short term ratings of those ratings agencies, or, if no credit rating is available, judged to be of comparable quality as determined by Thornburg. The Fund will not invest in any debt obligation rated at the time of purchase lower than BBB by S&P, Baa by Moody’s, the of equivalent short term ratings of those ratings agencies, or, if no credit rating is available, judged to be of comparable quality as determined by Thornburg. The Fund may purchase debt obligations such as corporate debt obligations, mortgage-backed securities, other asset-backed securities, municipal securities, and commercial paper and bankers’ acceptances. The Fund may purchase foreign securities of the same types and quality as the domestic securities it purchases when Thornburg believes these investments are consistent with the Fund’s objectives.

Because the magnitude of changes in the value of interest-bearing obligations is greater for obligations with longer terms given an equivalent change in interest rates, the Fund seeks to reduce changes in its share value by maintaining a portfolio of investments with a dollar-weighted average maturity or expected life normally of less than five years. As a result, the Fund also maintains a portfolio of investments having a dollar-weighted average effective duration of normally no more than five years. Duration is a measure of estimated sensitivity to interest rate changes. A portfolio with a longer average effective duration will typically be more sensitive to interest rate changes than a portfolio with a shorter average effective duration. Duration is commonly expressed as a number, which is the expected percentage change in an obligation’s price upon a 1% change in interest rates. For example, an obligation with a duration of 5 would be expected to change in price by approximately 5% in response to a 1% change in interest rates. During temporary periods the Fund’s portfolio maturity and average effective duration may be reduced for defensive purposes. There is no limitation on the maturity of any specific security the Fund may purchase, and the Fund may sell any security before it matures. The Fund also attempts to reduce changes in share value through credit analysis, selection and diversification.

The Fund ordinarily acquires and holds securities for investment rather than for realization of gains by short-term trading on market fluctuations. However, it may sell an investment prior to its scheduled maturity date to enhance income or reduce loss, to change the portfolio’s average duration or average maturity, to pursue other investment opportunities, in response to changes in the conditions or business of the investment’s issuer or changes in overall market conditions, or if, in Thornburg’s opinion, the investment no longer serves to achieve the Fund’s investment goals. The objective of preserving capital may prevent the Fund from obtaining the highest yields available.
Risk [Heading] rr_RiskHeading Principal Investment Risks
Risk Narrative [Text Block] rr_RiskNarrativeTextBlock

Although the Fund may acquire obligations issued or guaranteed by the U.S. government and its agencies, instrumentalities and enterprises, neither the Fund’s net asset value nor its dividends are guaranteed by the U.S. government. An investment in the Fund is not a deposit in any bank and is not insured or guaranteed by the Federal Deposit Insurance Corporation or any other government agency. Accordingly, the loss of money is a risk of investing in the Fund. The value of the Fund’s shares and its dividends may fluctuate from day to day and over time, and when you sell your shares they may be worth less than what you paid for them. If your sole objective is preservation of capital, then the Fund may not be suitable for you because the Fund’s share value will fluctuate, including as interest rates change. Investors whose sole objective is preservation of capital may wish to consider a high quality money market fund. The following is a summary of the principal risks of investing in the Fund.

Management Risk – The Fund is an actively managed portfolio, and the value of the Fund may be reduced if Thornburg pursues unsuccessful investments or fails to correctly identify risks affecting the broad economy or specific issuers in which the Fund invests.

Interest Rate Risk – When interest rates increase, the value of the Fund’s investments may decline and the Fund’s share value may be reduced. This effect is typically more pronounced for intermediate and longer-term obligations. This effect is also typically more pronounced for the Fund’s investment in mortgage- and other asset-backed securities, the value of which may fluctuate more significantly in response to interest rate changes. When interest rates decrease, the Fund’s dividends may decline.

Prepayment and Extension Risk – When market interest rates decline, certain debt obligations held by the Fund may be repaid more quickly than anticipated, requiring the Fund to reinvest the proceeds of those repayments in obligations which bear a lower interest rate. Conversely, when market interest rates increase, certain debt obligations held by the Fund may be repaid more slowly than anticipated, causing assets of the Fund to remain invested in relatively lower yielding obligations. These risks may be more pronounced for the Fund’s investments in mortgage-backed and asset-backed securities.

Credit Risk – All securities owned by the Fund may be subject to default, delays in payment, adverse legislation or other government action, or could be downgraded by ratings agencies, reducing the value of the Fund’s shares. Securities backed by the full faith and credit of the U.S. government, such as U.S. Treasury obligations, are commonly regarded as having small exposure to credit risk. Obligations of certain U.S. government agencies, instrumentalities and government sponsored enterprises (sometimes referred to as “agency obligations”) are not direct obligations of the United States, may not be backed by the full faith and credit of the U.S. government, and may have a greater exposure to credit risk. Although the U.S. government is required by law to provide credit support for some agency obligations, there is no assurance that the U.S. government would provide financial support for any such obligation on a default by the issuing agency, instrumentality or enterprise in the absence of a legal requirement to do so. As of the date of this Prospectus, securities backed by the full faith and credit of the U.S. government, and securities of U.S. government agencies, instrumentalities and enterprises which may be purchased by the Fund, are rated “Aaa” by Moody’s Investors Services or “AA+” by S&P Global Ratings. Ratings agencies may reduce the ratings of any securities in the future. Lower-rated or unrated obligations in which the Fund is permitted to invest may have, or may be perceived to have, greater risk of default and ratings downgrades.

Market and Economic Risk – The value of the Fund’s investments may decline and its share value may be reduced due to changes in general economic and market conditions. For example, a fall in worldwide demand for U.S. government securities or general economic decline could lower the value of those securities.

Risks Affecting Specific Issuers – The value of a debt obligation may decline in response to developments affecting the specific issuer of the obligation, even if other issuers or the overall economy are unaffected. These developments may include a variety of factors, including but not limited to management issues or other corporate disruption, a decline in revenues or profitability, an increase in costs, or an adverse effect on the issuer’s competitive position.

Foreign Investment Risk – Investments in the debt obligations of foreign issuers may involve risks including adverse fluctuations in currency exchange rates, political instability, confiscations, taxes or restrictions on currency exchange, difficulty in selling foreign investments, and reduced legal protection. These risks may be more pronounced for investments in developing countries. In addition, some foreign government debt obligations may be subject to default, delays in payment, adverse legislation or government action, or could be downgraded by ratings agencies.

Liquidity Risk – Due to a lack of demand in the marketplace or other factors, the Fund may not be able to sell promptly some or all of the obligations that it holds, or may only be able to sell obligations at less than desired prices.

Structured Products Risk – Investments in securities that are backed by, or represent interests in, an underlying pool of securities or other assets, including investments in mortgage- and asset-backed securities and in collateralized mortgage obligations and collateralized debt obligations, involve the risks associated with the underlying assets (e.g., the risk of default by mortgagors whose mortgages are included in a mortgage-backed security or collateralized mortgage obligation), and may also involve different or greater risks, including the risk that distributions from the underlying assets will be inadequate to make interest or other payments to the Fund, the risk that the issuer of the securities will fail to administer the underlying assets properly or become insolvent, and the risk that the securities will be less liquid than other Fund investments.

Cybersecurity and Operational Risk – Operational failures, cyber-attacks or other disruptions that affect the Fund’s service providers, the Fund’s counterparties, other market participants or the issuers of securities held by the Fund may adversely affect the Fund and its shareholders, including by causing losses for the Fund or impairing Fund operations.

Additional information about Fund investments, investment strategies, and risks of investing in the Fund appears beginning on page 61 of the Prospectus.
Risk Lose Money [Text] rr_RiskLoseMoney Accordingly, the loss of money is a risk of investing in the Fund.
RIsk Not Insured [Text] rr_RiskNotInsured An investment in the Fund is not a deposit in any bank and is not insured or guaranteed by the Federal Deposit Insurance Corporation or any other government agency.
Bar Chart and Performance Table [Heading] rr_BarChartAndPerformanceTableHeading Past Performance of the Fund
Performance Narrative [Text Block] rr_PerformanceNarrativeTextBlock

The following information provides some indication of the risks of investing in Limited Term Income Fund by showing how the Fund’s investment results vary from year to year. The bar chart shows how the annual total returns for Class R3 shares have been different in each full year shown. The average annual total return figures compare Class R3, Class R4, Class R5 and Class R6 share performance to the Bloomberg Barclays Intermediate US Government/Credit Total Return Index Value Unhedged, a broad measure of market performance. Past performance (before and after taxes) is not necessarily an indication of how the Fund will perform in the future. The performance information shown below is as of the calendar year ended December 31, 2021. Updated performance information may be obtained on the Thornburg website at www.thornburg.com or by calling 1-800-847-0200.
Performance Information Illustrates Variability of Returns [Text] rr_PerformanceInformationIllustratesVariabilityOfReturns The following information provides some indication of the risks of investing in Limited Term Income Fund by showing how the Fund’s investment results vary from year to year.
Performance Availability Phone [Text] rr_PerformanceAvailabilityPhone 1-800-847-0200
Performance Availability Website Address [Text] rr_PerformanceAvailabilityWebSiteAddress www.thornburg.com
Performance Past Does Not Indicate Future [Text] rr_PerformancePastDoesNotIndicateFuture Past performance (before and after taxes) is not necessarily an indication of how the Fund will perform in the future.
Bar Chart [Heading] rr_BarChartHeading Annual Total Returns – Class R3 Shares
Bar Chart Closing [Text Block] rr_BarChartClosingTextBlock

Total
Returns

Quarter
ended

Highest Quarterly Results

5.66%

6/30/2020

Lowest Quarterly Results

(2.08)%

6/30/2013
Performance Table Heading rr_PerformanceTableHeading Average Annual Total Returns (periods ended 12-31-21)
Performance Table Uses Highest Federal Rate rr_PerformanceTableUsesHighestFederalRate After-tax returns are calculated using the highest historical individual federal marginal income tax rates, and do not reflect state or local income taxes.
Performance Table Not Relevant to Tax Deferred rr_PerformanceTableNotRelevantToTaxDeferred Actual after-tax returns depend on an investor’s own tax situation and may differ from the returns shown, and after-tax returns shown are not relevant to investors who hold their Fund shares through tax-deferred arrangements, such as 401(k) plans or individual retirement accounts.
Performance Table One Class of after Tax Shown [Text] rr_PerformanceTableOneClassOfAfterTaxShown The after-tax returns shown relate only to Class R3 shares, and after-tax returns for other share classes will vary.
Performance Table Closing [Text Block] rr_PerformanceTableClosingTextBlock

After-tax returns are calculated using the highest historical individual federal marginal income tax rates, and do not reflect state or local income taxes. Actual after-tax returns depend on an investor’s own tax situation and may differ from the returns shown, and after-tax returns shown are not relevant to investors who hold their Fund shares through tax-deferred arrangements, such as 401(k) plans or individual retirement accounts. The after-tax returns shown relate only to Class R3 shares, and after-tax returns for other share classes will vary.
Retirement | Thornburg Limited Term Income Fund | Thornburg Limited Term Income Fund - Class R3  
Prospectus [Line Items] rr_ProspectusLineItems  
Trading Symbol dei_TradingSymbol THIRX
Maximum Sales Charge Imposed on Purchases (as a percentage of Offering Price) rr_MaximumSalesChargeImposedOnPurchasesOverOfferingPrice none
Maximum Deferred Sales Charge (as a percentage) rr_MaximumDeferredSalesChargeOverOther none
Management Fees (as a percentage of Assets) rr_ManagementFeesOverAssets 0.31%
Distribution and Service (12b-1) Fees rr_DistributionAndService12b1FeesOverAssets 0.50%
Other Expenses (as a percentage of Assets): rr_OtherExpensesOverAssets 0.21%
Expenses (as a percentage of Assets) rr_ExpensesOverAssets 1.02%
Fee Waiver or Reimbursement rr_FeeWaiverOrReimbursementOverAssets (0.03%) [73]
Net Expenses (as a percentage of Assets) rr_NetExpensesOverAssets 0.99%
Expense Example, with Redemption, 1 Year rr_ExpenseExampleYear01 $ 101
Expense Example, with Redemption, 3 Years rr_ExpenseExampleYear03 322
Expense Example, with Redemption, 5 Years rr_ExpenseExampleYear05 560
Expense Example, with Redemption, 10 Years rr_ExpenseExampleYear10 $ 1,245
Annual Return 2012 rr_AnnualReturn2012 7.42%
Annual Return 2013 rr_AnnualReturn2013 (0.27%)
Annual Return 2014 rr_AnnualReturn2014 3.36%
Annual Return 2015 rr_AnnualReturn2015 0.35%
Annual Return 2016 rr_AnnualReturn2016 3.00%
Annual Return 2017 rr_AnnualReturn2017 2.15%
Annual Return 2018 rr_AnnualReturn2018 0.82%
Annual Return 2019 rr_AnnualReturn2019 5.15%
Annual Return 2020 rr_AnnualReturn2020 7.13%
Annual Return 2021 rr_AnnualReturn2021 (1.30%)
Highest Quarterly Return, Label rr_HighestQuarterlyReturnLabel Highest Quarterly Results
Highest Quarterly Return, Date rr_BarChartHighestQuarterlyReturnDate Jun. 30, 2020
Highest Quarterly Return rr_BarChartHighestQuarterlyReturn 5.66%
Lowest Quarterly Return, Label rr_LowestQuarterlyReturnLabel Lowest Quarterly Results
Lowest Quarterly Return, Date rr_BarChartLowestQuarterlyReturnDate Jun. 30, 2013
Lowest Quarterly Return rr_BarChartLowestQuarterlyReturn (2.08%)
1 Year rr_AverageAnnualReturnYear01 (1.30%)
5 Years rr_AverageAnnualReturnYear05 2.75%
10 Years rr_AverageAnnualReturnYear10 2.74%
Retirement | Thornburg Limited Term Income Fund | Thornburg Limited Term Income Fund - Class R3 | After Taxes on Distributions  
Prospectus [Line Items] rr_ProspectusLineItems  
1 Year rr_AverageAnnualReturnYear01 (1.73%)
5 Years rr_AverageAnnualReturnYear05 1.85%
10 Years rr_AverageAnnualReturnYear10 1.78%
Retirement | Thornburg Limited Term Income Fund | Thornburg Limited Term Income Fund - Class R3 | After Taxes on Distributions and Sales  
Prospectus [Line Items] rr_ProspectusLineItems  
1 Year rr_AverageAnnualReturnYear01 (0.77%)
5 Years rr_AverageAnnualReturnYear05 1.72%
10 Years rr_AverageAnnualReturnYear10 1.70%
Retirement | Thornburg Limited Term Income Fund | Thornburg Limited Term Income Fund - Class R3 | Bloomberg Barclays Intermediate Government/Credit Index (reflects no deduction for fees, expenses, or taxes)  
Prospectus [Line Items] rr_ProspectusLineItems  
1 Year rr_AverageAnnualReturnYear01 (1.44%)
5 Years rr_AverageAnnualReturnYear05 2.91%
10 Years rr_AverageAnnualReturnYear10 2.38%
Retirement | Thornburg Limited Term Income Fund | Thornburg Limited Term Income Fund - Class R4  
Prospectus [Line Items] rr_ProspectusLineItems  
Trading Symbol dei_TradingSymbol THRIX
Maximum Sales Charge Imposed on Purchases (as a percentage of Offering Price) rr_MaximumSalesChargeImposedOnPurchasesOverOfferingPrice none
Maximum Deferred Sales Charge (as a percentage) rr_MaximumDeferredSalesChargeOverOther none
Management Fees (as a percentage of Assets) rr_ManagementFeesOverAssets 0.31%
Distribution and Service (12b-1) Fees rr_DistributionAndService12b1FeesOverAssets 0.25%
Other Expenses (as a percentage of Assets): rr_OtherExpensesOverAssets 0.63%
Expenses (as a percentage of Assets) rr_ExpensesOverAssets 1.19%
Fee Waiver or Reimbursement rr_FeeWaiverOrReimbursementOverAssets (0.20%) [73]
Net Expenses (as a percentage of Assets) rr_NetExpensesOverAssets 0.99%
Expense Example, with Redemption, 1 Year rr_ExpenseExampleYear01 $ 101
Expense Example, with Redemption, 3 Years rr_ExpenseExampleYear03 358
Expense Example, with Redemption, 5 Years rr_ExpenseExampleYear05 635
Expense Example, with Redemption, 10 Years rr_ExpenseExampleYear10 $ 1,425
1 Year rr_AverageAnnualReturnYear01 (1.30%)
5 Years rr_AverageAnnualReturnYear05 2.75%
Since Inception rr_AverageAnnualReturnSinceInception 2.41%
Inception Date rr_AverageAnnualReturnInceptionDate Feb. 01, 2014
Retirement | Thornburg Limited Term Income Fund | Thornburg Limited Term Income Fund - Class R4 | Bloomberg Barclays Intermediate Government/Credit Index (reflects no deduction for fees, expenses, or taxes)  
Prospectus [Line Items] rr_ProspectusLineItems  
1 Year rr_AverageAnnualReturnYear01 (1.44%)
5 Years rr_AverageAnnualReturnYear05 2.91%
Since Inception rr_AverageAnnualReturnSinceInception 2.51%
Retirement | Thornburg Limited Term Income Fund | Thornburg Limited Term Income Fund - Class R5  
Prospectus [Line Items] rr_ProspectusLineItems  
Trading Symbol dei_TradingSymbol THRRX
Maximum Sales Charge Imposed on Purchases (as a percentage of Offering Price) rr_MaximumSalesChargeImposedOnPurchasesOverOfferingPrice none
Maximum Deferred Sales Charge (as a percentage) rr_MaximumDeferredSalesChargeOverOther none
Management Fees (as a percentage of Assets) rr_ManagementFeesOverAssets 0.31%
Distribution and Service (12b-1) Fees rr_DistributionAndService12b1FeesOverAssets none
Other Expenses (as a percentage of Assets): rr_OtherExpensesOverAssets 0.38%
Expenses (as a percentage of Assets) rr_ExpensesOverAssets 0.69%
Fee Waiver or Reimbursement rr_FeeWaiverOrReimbursementOverAssets (0.20%) [73]
Net Expenses (as a percentage of Assets) rr_NetExpensesOverAssets 0.49%
Expense Example, with Redemption, 1 Year rr_ExpenseExampleYear01 $ 50
Expense Example, with Redemption, 3 Years rr_ExpenseExampleYear03 201
Expense Example, with Redemption, 5 Years rr_ExpenseExampleYear05 364
Expense Example, with Redemption, 10 Years rr_ExpenseExampleYear10 $ 840
1 Year rr_AverageAnnualReturnYear01 (0.80%)
5 Years rr_AverageAnnualReturnYear05 3.20%
Since Inception rr_AverageAnnualReturnSinceInception 2.92%
Inception Date rr_AverageAnnualReturnInceptionDate May 01, 2012
Retirement | Thornburg Limited Term Income Fund | Thornburg Limited Term Income Fund - Class R5 | Bloomberg Barclays Intermediate Government/Credit Index (reflects no deduction for fees, expenses, or taxes)  
Prospectus [Line Items] rr_ProspectusLineItems  
1 Year rr_AverageAnnualReturnYear01 (1.44%)
5 Years rr_AverageAnnualReturnYear05 2.91%
Since Inception rr_AverageAnnualReturnSinceInception 2.31%
Retirement | Thornburg Limited Term Income Fund | Thornburg Limited Term Income Fund - Class R6  
Prospectus [Line Items] rr_ProspectusLineItems  
Trading Symbol dei_TradingSymbol THRLX
Maximum Sales Charge Imposed on Purchases (as a percentage of Offering Price) rr_MaximumSalesChargeImposedOnPurchasesOverOfferingPrice none
Maximum Deferred Sales Charge (as a percentage) rr_MaximumDeferredSalesChargeOverOther none
Management Fees (as a percentage of Assets) rr_ManagementFeesOverAssets 0.31%
Distribution and Service (12b-1) Fees rr_DistributionAndService12b1FeesOverAssets none
Other Expenses (as a percentage of Assets): rr_OtherExpensesOverAssets 0.12%
Expenses (as a percentage of Assets) rr_ExpensesOverAssets 0.43%
Fee Waiver or Reimbursement rr_FeeWaiverOrReimbursementOverAssets (0.01%) [73]
Net Expenses (as a percentage of Assets) rr_NetExpensesOverAssets 0.42%
Expense Example, with Redemption, 1 Year rr_ExpenseExampleYear01 $ 43
Expense Example, with Redemption, 3 Years rr_ExpenseExampleYear03 137
Expense Example, with Redemption, 5 Years rr_ExpenseExampleYear05 240
Expense Example, with Redemption, 10 Years rr_ExpenseExampleYear10 $ 541
1 Year rr_AverageAnnualReturnYear01 (0.73%)
Since Inception rr_AverageAnnualReturnSinceInception 3.42%
Inception Date rr_AverageAnnualReturnInceptionDate Apr. 10, 2017
Retirement | Thornburg Limited Term Income Fund | Thornburg Limited Term Income Fund - Class R6 | Bloomberg Barclays Intermediate Government/Credit Index (reflects no deduction for fees, expenses, or taxes)  
Prospectus [Line Items] rr_ProspectusLineItems  
1 Year rr_AverageAnnualReturnYear01 (1.44%)
Since Inception rr_AverageAnnualReturnSinceInception 2.88%
Retirement | Thornburg Strategic Income Fund  
Prospectus [Line Items] rr_ProspectusLineItems  
Risk/Return [Heading] rr_RiskReturnHeading Strategic Income Fund
Objective [Heading] rr_ObjectiveHeading Investment Goal
Objective, Primary [Text Block] rr_ObjectivePrimaryTextBlock

The Fund’s primary investment goal is to seek a high level of current income.
Objective, Secondary [Text Block] rr_ObjectiveSecondaryTextBlock

The Fund’s secondary investment goal is some long-term capital appreciation.
Expense [Heading] rr_ExpenseHeading Fees and Expenses of the Fund
Expense Narrative [Text Block] rr_ExpenseNarrativeTextBlock

This table describes the fees and expenses that you may pay if you buy and hold shares of the Fund.

Shareholder Fees Caption [Text] rr_ShareholderFeesCaption Shareholder Fees (fees paid directly from your investment)
Operating Expenses Caption [Text] rr_OperatingExpensesCaption Annual Fund Operating Expenses (expenses that you pay each year as a percentage of the value of your investment)
Fee Waiver or Reimbursement over Assets, Date of Termination rr_FeeWaiverOrReimbursementOverAssetsDateOfTermination February 1, 2023
Portfolio Turnover [Heading] rr_PortfolioTurnoverHeading Portfolio Turnover.
Portfolio Turnover [Text Block] rr_PortfolioTurnoverTextBlock

The Fund pays transaction costs, such as commissions, when it buys and sells securities (or “turns over”) its portfolio. A higher portfolio turnover rate may indicate higher transaction costs and may result in higher taxes when Fund shares are held in a taxable account. These costs, which are not reflected in Annual Fund Operating Expenses or in the Example, affect the Fund’s performance. During the most recent fiscal year, the Fund’s portfolio turnover rate was 28.55% of the average value of its portfolio.
Portfolio Turnover, Rate rr_PortfolioTurnoverRate 28.55%
Expense Example [Heading] rr_ExpenseExampleHeading Example.
Expense Example Narrative [Text Block] rr_ExpenseExampleNarrativeTextBlock

This Example is intended to help you compare the cost of investing in the Fund with the cost of investing in other mutual funds.

The Example assumes that you invest $10,000 in the Fund for the time periods indicated and then redeem all of your shares at the end of those periods. The Example also assumes that your investment has a 5% return each year, dividends and distributions are reinvested, and that the Fund’s operating expenses remain the same. Although your actual costs may be higher or lower, based on these assumptions (and giving effect to fee waivers and expense reimbursements in the first year), your costs would be:
Strategy [Heading] rr_StrategyHeading Principal Investment Strategies
Strategy Narrative [Text Block] rr_StrategyNarrativeTextBlock

The Fund pursues its investment goals by investing in a broad range of income-producing investments from throughout the world, primarily including debt obligations. The Fund expects, under normal conditions, to invest a majority of its assets in the debt obligations described below.

The Fund may invest in debt obligations of any kind, of any quality, and of any maturity. The Fund expects, under normal conditions, to select a majority of its investments from among the following types of debt obligations:

•bonds and other debt obligations issued by domestic and foreign companies of any size (including lower-rated “high yield” or “junk” bonds)

•mortgage-backed securities and other asset-backed securities, including commercial mortgage-backed securities

•convertible debt obligations

•obligations issued by foreign governments (including developing countries)

•collateralized mortgage obligations (“CMOs”), collateralized debt obligations (“CDOs”), collateralized bond obligations (“CBOs”), and collateralized loan obligations (“CLOs”)

•obligations of the U.S. government and its agencies and sponsored enterprises

•structured notes

•zero coupon bonds and “stripped” securities

•taxable municipal obligations and participations in municipal obligations

The Fund’s investments are determined by individual issuer and industry analysis. Investment decisions are based on domestic and international economic developments, outlooks for securities markets, interest rates and inflation, the supply and demand for debt securities, and analysis of specific issuers.

The Fund ordinarily acquires and holds securities for investment rather than for realization of gains by short-term trading on market fluctuations. However, it may sell an investment prior to its scheduled maturity date to enhance income or reduce loss, to change the portfolio’s average duration or average maturity, to pursue other investment opportunities, in response to changes in the conditions or business of the investment’s issuer or changes in overall market conditions, or if, in Thornburg’s opinion, the investment no longer serves to achieve the Fund’s investment goals. The objective of preserving capital may prevent the Fund from obtaining the highest yields available.
Risk [Heading] rr_RiskHeading Principal Investment Risks
Risk Narrative [Text Block] rr_RiskNarrativeTextBlock

An investment in the Fund is not a deposit in any bank and is not insured or guaranteed by the Federal Deposit Insurance Corporation or any other government agency. Accordingly, the loss of money is a risk of investing in the Fund. The value of the Fund’s shares and its dividends may fluctuate from day to day and over time, and when you sell your shares they may be worth less than what you paid for them. The following is a summary of the principal risks of investing in the Fund. Please note that because the Fund’s objective is to provide high current income, the Fund invests with an emphasis on income, rather than stability of net asset value.

Management Risk – The Fund is an actively managed portfolio, and the value of the Fund may be reduced if Thornburg pursues unsuccessful investments or fails to correctly identify risks affecting the broad economy or specific issuers in which the Fund invests.

Interest Rate Risk – When interest rates increase, the value of the Fund’s investments may decline and the Fund’s share value may be reduced. This effect is typically more pronounced for intermediate and longer-term obligations. This effect is also typically more pronounced for mortgage- and other asset-backed securities, the value of which may fluctuate more significantly in response to interest rate changes. When interest rates decrease, the Fund’s dividends may decline.

Prepayment and Extension Risk – When market interest rates decline, certain debt obligations held by the Fund may be repaid more quickly than anticipated, requiring the Fund to reinvest the proceeds of those repayments in obligations which bear a lower interest rate. Conversely, when market interest rates increase, certain debt obligations held by the Fund may be repaid more slowly than anticipated, causing assets of the Fund to remain invested in relatively lower yielding obligations. These risks may be more pronounced for the Fund’s investments in mortgage-backed and asset-backed securities.

Credit Risk – If obligations held by the Fund are downgraded by ratings agencies or go into default, or if management action, legislation or other government action reduces the ability of issuers to pay principal and interest when due, the value of those obligations may decline and the Fund’s share value and the dividends paid by the Fund may be reduced. Because the ability of an issuer of a lower-rated or unrated obligation to pay principal and interest when due is typically less certain than for an issuer of a higher-rated obligation, lower-rated and unrated obligations are generally more vulnerable than higher-rated obligations to default, to ratings downgrades, and to liquidity risk. Debt obligations backed by so-called “subprime” mortgages may also be subject to a greater risk of default or downgrade. Debt obligations issued by the U.S. government or its agencies, instrumentalities and government sponsored enterprises are also subject to credit risk. Securities backed by the full faith and credit of the U.S. government, such as U.S. Treasury obligations, are commonly regarded as having small exposure to credit risk. Obligations of certain U.S. agencies, instrumentalities and enterprises (sometimes referred to as “agency obligations”) are not direct obligations of the U.S. government, may not be backed by the full faith and credit of the U.S. government, and may have a greater exposure to credit risk.

High Yield Risk – Debt obligations that are rated below investment grade and unrated obligations of similar credit quality (commonly referred to as “junk” or “high yield” bonds) may have a substantial risk of loss. These obligations are generally considered to be speculative with respect to the issuer’s ability to pay interest and principal when due. These obligations may be subject to greater price volatility than investment grade obligations, and their prices may decline significantly in periods of general economic difficulty or in response to adverse publicity, changes in investor perceptions or other factors. These obligations may also be subject to greater liquidity risk.

Market and Economic Risk – The value of the Fund’s investments may decline and its share value may be reduced due to changes in general economic and market conditions. This effect is typically more pronounced for lower-rated and unrated debt obligations (including particularly “junk” or “high yield” bonds), the value of which may fluctuate more significantly in response to poor economic growth or other changes in market conditions, political, economic and legal developments. The market value of any zero coupon bonds or “stripped” securities that the Fund may purchase will typically be more volatile than the value of a comparable, interest-paying bond. Additionally, zero coupon bonds and “stripped” securities are subject to the risk that the Fund may have to recognize income on its investment and make distributions to shareholders before it has received any cash payments on its investment.

Risks Affecting Specific Issuers – The value of a debt obligation may decline in response to developments affecting the specific issuer of the obligation or security, even if the overall industry or economy is unaffected. These developments may include a variety of factors, including but not limited to management issues or other corporate disruption, a decline in revenues or profitability, an increase in costs, or an adverse effect on the issuer’s competitive position.

Liquidity Risk – Due to a lack of demand in the marketplace or other factors, the Fund may not be able to sell some or all of its investments promptly, or may only be able to sell investments at less than desired prices. The market for lower-rated and unrated debt obligations (including particularly “junk” or “high yield” bonds) and debt obligations backed by so-called “subprime” mortgages may be less liquid than the market for other obligations, making it difficult for the Fund to value its investment in a lower-rated or unrated obligation or to sell the investment in a timely manner or at an acceptable price.

Small and Mid-Cap Company Risk – Investments in small-capitalization companies and mid-capitalization companies may involve additional risks, which may be relatively higher with smaller companies. These additional risks may result from limited product lines, more limited access to markets and financial resources, greater vulnerability to competition and changes in markets, lack of management depth, increased volatility in share price, and possible difficulties in valuing or selling these investments.

Foreign Investment Risk – Investments in the debt obligations of foreign issuers may involve risks including adverse fluctuations in currency exchange rates, political instability, confiscations, taxes or restrictions on currency exchange, difficulty in selling foreign investments, and reduced legal protection. In addition, some foreign government debt obligations may be subject to default, delays in payment, adverse legislation or government action, or could be downgraded by ratings agencies.

Developing Country Risk – The risks which may affect investments in foreign issuers (see “Foreign Investment Risk,” above) may be more pronounced for investments in developing countries because the economies of those countries are usually less diversified, communications, transportation and economic infrastructures are less developed, and developing countries ordinarily have less established legal, political, business and social frameworks. At times the prices of debt obligations of a developing country issuer may be extremely volatile. An issuer domiciled in a developed country may be similarly affected by these developing country risks to the extent that the issuer conducts its business in developing countries.

Foreign Currency Risk – Fluctuations in currency exchange rates can adversely affect the value of the Fund’s foreign investments. Such fluctuations may occur for a number of reasons, including market and economic conditions, or a government’s decision to devalue its currency or impose currency controls.

Structured Products Risk – Investments in securities that are backed by, or represent interests in, an underlying pool of securities or other assets, including investments in mortgage- and asset-backed securities and in collateralized mortgage obligations and collateralized debt obligations, involve the risks associated with the underlying assets (e.g., the risk of default by mortgagors whose mortgages are included in a mortgage-backed security or collateralized mortgage obligation), and may also involve different or greater risks, including the risk that distributions from the underlying assets will be inadequate to make interest or other payments to the Fund, the risk that the issuer of the securities will fail to administer the underlying assets properly or become insolvent, and the risk that the securities will be less liquid than other Fund investments.

Cybersecurity and Operational Risk – Operational failures, cyber-attacks or other disruptions that affect the Fund’s service providers, the Fund’s counterparties, other market participants or the issuers of securities held by the Fund may adversely affect the Fund and its shareholders, including by causing losses for the Fund or impairing Fund operations.

Additional information about Fund investments, investment strategies and risks of investing in the Fund appears below beginning on page 61 of the Prospectus.
Risk Lose Money [Text] rr_RiskLoseMoney Accordingly, the loss of money is a risk of investing in the Fund.
RIsk Not Insured [Text] rr_RiskNotInsured An investment in the Fund is not a deposit in any bank and is not insured or guaranteed by the Federal Deposit Insurance Corporation or any other government agency.
Bar Chart and Performance Table [Heading] rr_BarChartAndPerformanceTableHeading Past Performance of the Fund
Performance Narrative [Text Block] rr_PerformanceNarrativeTextBlock

The following information provides some indication of the risks of investing in Strategic Income Fund by showing how the Fund’s investment results vary from year to year. The bar chart shows the annual total return for Class R3 shares in the one full year shown. The average annual total return figures compare Class R3, Class R4, Class R5 and Class R6 share performance to the Bloomberg Barclays US Universal Total Return Index Value Unhedged, a broad measure of market performance, and to a Blended Benchmark comprised of 80% Bloomberg Barclays US Aggregate Bond Total Return Value USD, which represents a broad measure of bond market performance, and 20% MSCI World Net Total Return USD Index, which represents a broad measure of equity market performance in developed markets. Past performance (before and after taxes) is not necessarily an indication of how the Fund will perform in the future. The performance information shown below is as of the calendar year ended December 31, 2021. Updated performance information may be obtained on the Thornburg website at www.thornburg.com or by calling 1-800-847-0200.
Performance Information Illustrates Variability of Returns [Text] rr_PerformanceInformationIllustratesVariabilityOfReturns The following information provides some indication of the risks of investing in Strategic Income Fund by showing how the Fund’s investment results vary from year to year.
Performance Availability Phone [Text] rr_PerformanceAvailabilityPhone 1-800-847-0200
Performance Availability Website Address [Text] rr_PerformanceAvailabilityWebSiteAddress www.thornburg.com
Performance Past Does Not Indicate Future [Text] rr_PerformancePastDoesNotIndicateFuture Past performance (before and after taxes) is not necessarily an indication of how the Fund will perform in the future.
Bar Chart [Heading] rr_BarChartHeading Annual Total Returns – Class R3 Shares
Bar Chart Closing [Text Block] rr_BarChartClosingTextBlock

Total
Returns

Quarter
ended

Highest Quarterly Results

7.85%

6/30/2020

Lowest Quarterly Results

(5.71)%

3/31/2020
Performance Table Heading rr_PerformanceTableHeading Average Annual Total Returns (periods ended 12-31-21)
Performance Table Uses Highest Federal Rate rr_PerformanceTableUsesHighestFederalRate After-tax returns are calculated using the highest historical individual federal marginal income tax rates, and do not reflect state or local income taxes.
Performance Table Not Relevant to Tax Deferred rr_PerformanceTableNotRelevantToTaxDeferred Actual after-tax returns depend on an investor’s own tax situation and may differ from the returns shown, and after-tax returns shown are not relevant to investors who hold their Fund shares through tax-deferred arrangements, such as 401(k) plans or individual retirement accounts.
Performance Table One Class of after Tax Shown [Text] rr_PerformanceTableOneClassOfAfterTaxShown The after-tax returns shown relate only to Class R3 shares, and after-tax returns for other share classes will vary.
Performance Table Closing [Text Block] rr_PerformanceTableClosingTextBlock

After-tax returns are calculated using the highest historical individual federal marginal income tax rates, and do not reflect state or local income taxes. Actual after-tax returns depend on an investor’s own tax situation and may differ from the returns shown, and after-tax returns shown are not relevant to investors who hold their Fund shares through tax-deferred arrangements, such as 401(k) plans or individual retirement accounts. The after-tax returns shown relate only to Class R3 shares, and after-tax returns for other share classes will vary.
Retirement | Thornburg Strategic Income Fund | Thornburg Strategic Income Fund - Class R3  
Prospectus [Line Items] rr_ProspectusLineItems  
Trading Symbol dei_TradingSymbol TSIRX
Maximum Sales Charge Imposed on Purchases (as a percentage of Offering Price) rr_MaximumSalesChargeImposedOnPurchasesOverOfferingPrice none
Maximum Deferred Sales Charge (as a percentage) rr_MaximumDeferredSalesChargeOverOther none
Management Fees (as a percentage of Assets) rr_ManagementFeesOverAssets 0.60%
Distribution and Service (12b-1) Fees rr_DistributionAndService12b1FeesOverAssets 0.50%
Other Expenses (as a percentage of Assets): rr_OtherExpensesOverAssets 2.06%
Expenses (as a percentage of Assets) rr_ExpensesOverAssets 3.16%
Fee Waiver or Reimbursement rr_FeeWaiverOrReimbursementOverAssets (1.91%) [74]
Net Expenses (as a percentage of Assets) rr_NetExpensesOverAssets 1.25%
Expense Example, with Redemption, 1 Year rr_ExpenseExampleYear01 $ 127
Expense Example, with Redemption, 3 Years rr_ExpenseExampleYear03 795
Expense Example, with Redemption, 5 Years rr_ExpenseExampleYear05 1,488
Expense Example, with Redemption, 10 Years rr_ExpenseExampleYear10 $ 3,334
Annual Return 2013 rr_AnnualReturn2013 5.87%
Annual Return 2014 rr_AnnualReturn2014 3.15%
Annual Return 2015 rr_AnnualReturn2015 (2.43%)
Annual Return 2016 rr_AnnualReturn2016 7.71%
Annual Return 2017 rr_AnnualReturn2017 5.95%
Annual Return 2018 rr_AnnualReturn2018 0.13%
Annual Return 2019 rr_AnnualReturn2019 7.23%
Annual Return 2020 rr_AnnualReturn2020 7.55%
Annual Return 2021 rr_AnnualReturn2021 2.11%
Highest Quarterly Return, Label rr_HighestQuarterlyReturnLabel Highest Quarterly Results
Highest Quarterly Return, Date rr_BarChartHighestQuarterlyReturnDate Jun. 30, 2020
Highest Quarterly Return rr_BarChartHighestQuarterlyReturn 7.85%
Lowest Quarterly Return, Label rr_LowestQuarterlyReturnLabel Lowest Quarterly Results
Lowest Quarterly Return, Date rr_BarChartLowestQuarterlyReturnDate Mar. 31, 2020
Lowest Quarterly Return rr_BarChartLowestQuarterlyReturn (5.71%)
1 Year rr_AverageAnnualReturnYear01 2.11%
5 Years rr_AverageAnnualReturnYear05 4.55%
Since Inception rr_AverageAnnualReturnSinceInception 4.48%
Inception Date rr_AverageAnnualReturnInceptionDate May 01, 2012
Retirement | Thornburg Strategic Income Fund | Thornburg Strategic Income Fund - Class R3 | After Taxes on Distributions  
Prospectus [Line Items] rr_ProspectusLineItems  
1 Year rr_AverageAnnualReturnYear01 0.68%
5 Years rr_AverageAnnualReturnYear05 3.20%
Since Inception rr_AverageAnnualReturnSinceInception 2.71%
Retirement | Thornburg Strategic Income Fund | Thornburg Strategic Income Fund - Class R3 | After Taxes on Distributions and Sales  
Prospectus [Line Items] rr_ProspectusLineItems  
1 Year rr_AverageAnnualReturnYear01 1.25%
5 Years rr_AverageAnnualReturnYear05 2.91%
Since Inception rr_AverageAnnualReturnSinceInception 2.66%
Retirement | Thornburg Strategic Income Fund | Thornburg Strategic Income Fund - Class R3 | Blended Benchmark (reflects no deduction for fees, expenses, or U.S. taxes)  
Prospectus [Line Items] rr_ProspectusLineItems  
1 Year rr_AverageAnnualReturnYear01 2.85%
5 Years rr_AverageAnnualReturnYear05 5.97%
Since Inception rr_AverageAnnualReturnSinceInception 4.79%
Retirement | Thornburg Strategic Income Fund | Thornburg Strategic Income Fund - Class R3 | Bloomberg Barclays U.S. Universal Index (reflects no deduction for fees, expenses, or taxes)  
Prospectus [Line Items] rr_ProspectusLineItems  
1 Year rr_AverageAnnualReturnYear01 (1.10%)
5 Years rr_AverageAnnualReturnYear05 3.84%
Since Inception rr_AverageAnnualReturnSinceInception 3.23%
Retirement | Thornburg Strategic Income Fund | Thornburg Strategic Income Fund - Class R4  
Prospectus [Line Items] rr_ProspectusLineItems  
Trading Symbol dei_TradingSymbol TSRIX
Maximum Sales Charge Imposed on Purchases (as a percentage of Offering Price) rr_MaximumSalesChargeImposedOnPurchasesOverOfferingPrice none
Maximum Deferred Sales Charge (as a percentage) rr_MaximumDeferredSalesChargeOverOther none
Management Fees (as a percentage of Assets) rr_ManagementFeesOverAssets 0.60%
Distribution and Service (12b-1) Fees rr_DistributionAndService12b1FeesOverAssets 0.25%
Other Expenses (as a percentage of Assets): rr_OtherExpensesOverAssets 1.43%
Expenses (as a percentage of Assets) rr_ExpensesOverAssets 2.28%
Fee Waiver or Reimbursement rr_FeeWaiverOrReimbursementOverAssets (1.03%) [74]
Net Expenses (as a percentage of Assets) rr_NetExpensesOverAssets 1.25%
Expense Example, with Redemption, 1 Year rr_ExpenseExampleYear01 $ 127
Expense Example, with Redemption, 3 Years rr_ExpenseExampleYear03 613
Expense Example, with Redemption, 5 Years rr_ExpenseExampleYear05 1,126
Expense Example, with Redemption, 10 Years rr_ExpenseExampleYear10 $ 2,536
1 Year rr_AverageAnnualReturnYear01 2.20%
5 Years rr_AverageAnnualReturnYear05 4.55%
Since Inception rr_AverageAnnualReturnSinceInception 3.85%
Inception Date rr_AverageAnnualReturnInceptionDate Feb. 01, 2014
Retirement | Thornburg Strategic Income Fund | Thornburg Strategic Income Fund - Class R4 | Blended Benchmark (reflects no deduction for fees, expenses, or U.S. taxes)  
Prospectus [Line Items] rr_ProspectusLineItems  
1 Year rr_AverageAnnualReturnYear01 2.85%
5 Years rr_AverageAnnualReturnYear05 5.97%
Since Inception rr_AverageAnnualReturnSinceInception 4.95%
Retirement | Thornburg Strategic Income Fund | Thornburg Strategic Income Fund - Class R4 | Bloomberg Barclays U.S. Universal Index (reflects no deduction for fees, expenses, or taxes)  
Prospectus [Line Items] rr_ProspectusLineItems  
1 Year rr_AverageAnnualReturnYear01 (1.10%)
5 Years rr_AverageAnnualReturnYear05 3.84%
Since Inception rr_AverageAnnualReturnSinceInception 3.50%
Retirement | Thornburg Strategic Income Fund | Thornburg Strategic Income Fund - Class R5  
Prospectus [Line Items] rr_ProspectusLineItems  
Trading Symbol dei_TradingSymbol TSRRX
Maximum Sales Charge Imposed on Purchases (as a percentage of Offering Price) rr_MaximumSalesChargeImposedOnPurchasesOverOfferingPrice none
Maximum Deferred Sales Charge (as a percentage) rr_MaximumDeferredSalesChargeOverOther none
Management Fees (as a percentage of Assets) rr_ManagementFeesOverAssets 0.60%
Distribution and Service (12b-1) Fees rr_DistributionAndService12b1FeesOverAssets none
Other Expenses (as a percentage of Assets): rr_OtherExpensesOverAssets 0.32%
Expenses (as a percentage of Assets) rr_ExpensesOverAssets 0.92%
Fee Waiver or Reimbursement rr_FeeWaiverOrReimbursementOverAssets (0.32%) [74]
Net Expenses (as a percentage of Assets) rr_NetExpensesOverAssets 0.60%
Expense Example, with Redemption, 1 Year rr_ExpenseExampleYear01 $ 61
Expense Example, with Redemption, 3 Years rr_ExpenseExampleYear03 261
Expense Example, with Redemption, 5 Years rr_ExpenseExampleYear05 478
Expense Example, with Redemption, 10 Years rr_ExpenseExampleYear10 $ 1,102
1 Year rr_AverageAnnualReturnYear01 2.78%
5 Years rr_AverageAnnualReturnYear05 5.20%
Since Inception rr_AverageAnnualReturnSinceInception 4.95%
Inception Date rr_AverageAnnualReturnInceptionDate May 01, 2012
Retirement | Thornburg Strategic Income Fund | Thornburg Strategic Income Fund - Class R5 | Blended Benchmark (reflects no deduction for fees, expenses, or U.S. taxes)  
Prospectus [Line Items] rr_ProspectusLineItems  
1 Year rr_AverageAnnualReturnYear01 2.85%
5 Years rr_AverageAnnualReturnYear05 5.97%
Since Inception rr_AverageAnnualReturnSinceInception 4.79%
Retirement | Thornburg Strategic Income Fund | Thornburg Strategic Income Fund - Class R5 | Bloomberg Barclays U.S. Universal Index (reflects no deduction for fees, expenses, or taxes)  
Prospectus [Line Items] rr_ProspectusLineItems  
1 Year rr_AverageAnnualReturnYear01 (1.10%)
5 Years rr_AverageAnnualReturnYear05 3.84%
Since Inception rr_AverageAnnualReturnSinceInception 3.23%
Retirement | Thornburg Strategic Income Fund | Thornburg Strategic Income Fund - Class R6  
Prospectus [Line Items] rr_ProspectusLineItems  
Trading Symbol dei_TradingSymbol TSRSX
Maximum Sales Charge Imposed on Purchases (as a percentage of Offering Price) rr_MaximumSalesChargeImposedOnPurchasesOverOfferingPrice none
Maximum Deferred Sales Charge (as a percentage) rr_MaximumDeferredSalesChargeOverOther none
Management Fees (as a percentage of Assets) rr_ManagementFeesOverAssets 0.60%
Distribution and Service (12b-1) Fees rr_DistributionAndService12b1FeesOverAssets none
Other Expenses (as a percentage of Assets): rr_OtherExpensesOverAssets 0.15%
Expenses (as a percentage of Assets) rr_ExpensesOverAssets 0.75%
Fee Waiver or Reimbursement rr_FeeWaiverOrReimbursementOverAssets (0.22%) [74]
Net Expenses (as a percentage of Assets) rr_NetExpensesOverAssets 0.53%
Expense Example, with Redemption, 1 Year rr_ExpenseExampleYear01 $ 54
Expense Example, with Redemption, 3 Years rr_ExpenseExampleYear03 218
Expense Example, with Redemption, 5 Years rr_ExpenseExampleYear05 395
Expense Example, with Redemption, 10 Years rr_ExpenseExampleYear10 $ 910
1 Year rr_AverageAnnualReturnYear01 2.85%
Since Inception rr_AverageAnnualReturnSinceInception 5.15%
Inception Date rr_AverageAnnualReturnInceptionDate Apr. 10, 2017
Retirement | Thornburg Strategic Income Fund | Thornburg Strategic Income Fund - Class R6 | Blended Benchmark (reflects no deduction for fees, expenses, or U.S. taxes)  
Prospectus [Line Items] rr_ProspectusLineItems  
1 Year rr_AverageAnnualReturnYear01 2.85%
Since Inception rr_AverageAnnualReturnSinceInception 5.87%
Retirement | Thornburg Strategic Income Fund | Thornburg Strategic Income Fund - Class R6 | Bloomberg Barclays U.S. Universal Index (reflects no deduction for fees, expenses, or taxes)  
Prospectus [Line Items] rr_ProspectusLineItems  
1 Year rr_AverageAnnualReturnYear01 (1.10%)
Since Inception rr_AverageAnnualReturnSinceInception 3.77%
[1] Up to a 1.00% contingent deferred sales charge (CDSC) is imposed on redemptions of any part or all of a purchase of $1 million or more within 12 months of purchase.
[2] Imposed only on redemptions of Class C shares within 12 months of purchase.
[3] Thornburg Investment Management, Inc. (“Thornburg”) has contractually agreed to waive fees and reimburse expenses incurred by the Fund so that actual Class I expenses (excluding taxes, interest expenses, 12b-1 distribution and service fees, acquired fund fees and expenses, brokerage commissions, borrowing costs, expenses relating to short sales, and unusual expenses such as contingency fees or litigation costs) do not exceed 0.99%. The agreement to waive fees and reimburse expenses may be terminated by the Fund’s Trustees at any time, but may not be terminated by Thornburg before February 1, 2023, unless Thornburg ceases to be the investment advisor of the Fund prior to that date. Thornburg may recoup amounts waived or reimbursed during the Fund’s fiscal year if actual expenses fall below the expense cap during that same fiscal year.
[4] Up to a 1.00% contingent deferred sales charge (CDSC) is imposed on redemptions of any part or all of a purchase of $1 million or more within 12 months of purchase.
[5] European Union tax reclaim collection fees are considered extraordinary expenses and are excluded from the Fund’s Other Expenses. If such fees were included, the Fund’s Other Expenses for Classes A, I and C would have been 0.59%, 0.52% and 0.50%, respectively.
[6] Imposed only on redemptions of Class C shares within 12 months of purchase.
[7] Thornburg Investment Management, Inc. (“Thornburg”) has contractually agreed to waive fees and reimburse expenses incurred by the Fund so that actual Class I expenses (excluding taxes, interest expenses, 12b-1 distribution and service fees, acquired fund fees and expenses, brokerage commissions, borrowing costs, expenses relating to short sales, and unusual expenses such as contingency fees or litigation costs) do not exceed 0.90%. The agreement to waive fees and reimburse expenses may be terminated by the Fund’s Trustees at any time, but may not be terminated by Thornburg before February 1, 2023, unless Thornburg ceases to be the investment advisor of the Fund prior to that date. Thornburg may recoup amounts waived or reimbursed during the Fund’s fiscal year if actual expenses fall below the expense cap during that same fiscal year.
[8] Up to a 1.00% contingent deferred sales charge (CDSC) is imposed on redemptions of any part or all of a purchase of $1 million or more within 12 months of purchase.
[9] Thornburg Investment Management, Inc. (“Thornburg”) has contractually agreed to waive fees and reimburse expenses incurred by the Fund so that actual Class C and Class I expenses (excluding taxes, interest expenses, 12b-1 distribution and service fees, acquired fund fees and expenses, brokerage commissions, borrowing costs, expenses relating to short sales, and unusual expenses such as contingency fees or litigation costs) do not exceed 2.19% and 0.90%, respectively. The agreement to waive fees and reimburse expenses may be terminated by the Fund’s Trustees at any time, but may not be terminated by Thornburg before February 1, 2023, unless Thornburg ceases to be the investment advisor of the Fund prior to that date. Thornburg may recoup amounts waived or reimbursed during the Fund’s fiscal year if actual expenses fall below the expense cap during that same fiscal year.
[10] Imposed only on redemptions of Class C shares within 12 months of purchase.
[11] Up to a 1.00% contingent deferred sales charge (CDSC) is imposed on redemptions of any part or all of a purchase of $1 million or more within 12 months of purchase.
[12] European Union tax reclaim collection fees are considered extraordinary expenses and are excluded from the Fund’s Other Expenses. If such fees were included, the Fund’s Other Expenses for Classes A, I and C would have been 0.22%, 0.27% and 0.20%, respectively.
[13] Imposed only on redemptions of Class C shares within 12 months of purchase.
[14] Up to a 1.00% contingent deferred sales charge (CDSC) is imposed on redemptions of any part or all of a purchase of $1 million or more within 12 months of purchase.
[15] Imposed only on redemptions of Class C shares within 12 months of purchase.
[16] Thornburg Investment Management, Inc. (“Thornburg”) has contractually agreed to waive fees and reimburse expenses incurred by the Fund so that actual Class I expenses (excluding taxes, interest expenses, 12b-1 distribution and service fees, acquired fund fees and expenses, brokerage commissions, borrowing costs, expenses relating to short sales, and unusual expenses such as contingency fees or litigation costs) do not exceed 1.04%. The agreement to waive fees and reimburse expenses may be terminated by the Fund’s Trustees at any time, but may not be terminated by Thornburg before February 1, 2023, unless Thornburg ceases to be the investment advisor of the Fund prior to that date. Thornburg may recoup amounts waived or reimbursed during the Fund’s fiscal year if actual expenses fall below the expense cap during that same fiscal year.
[17] Up to a 1.00% contingent deferred sales charge (CDSC) is imposed on redemptions of any part or all of a purchase of $1 million or more within 12 months of purchase.
[18] European Union tax reclaim collection fees are considered extraordinary expenses and are excluded from the Fund’s Other Expenses. If such fees were included, the Fund’s Other Expenses for Classes A, I and C would have been 0.23%, 0.30% and 0.23%, respectively.
[19] Imposed only on redemptions of Class C shares within 12 months of purchase.
[20] Thornburg Investment Management, Inc. (“Thornburg”) has contractually agreed to waive fees and reimburse expenses incurred by the Fund so that actual Class I expenses (excluding taxes, interest expenses, 12b-1 distribution and service fees, acquired fund fees and expenses, brokerage commissions, borrowing costs, expenses relating to short sales, and unusual expenses such as contingency fees or litigation costs) do not exceed 0.95%. The agreement to waive fees and reimburse expenses may be terminated by the Fund’s Trustees at any time, but may not be terminated by Thornburg before February 1, 2023, unless Thornburg ceases to be the investment advisor of the Fund prior to that date. Thornburg may recoup amounts waived or reimbursed during the Fund’s fiscal year if actual expenses fall below the expense cap during that same fiscal year.
[21] Up to a 1.00% contingent deferred sales charge (CDSC) is imposed on redemptions of any part or all of a purchase of $1 million or more within 12 months of purchase.
[22] Imposed only on redemptions of Class C shares within 12 months of purchase.
[23] Thornburg Investment Management, Inc. (“Thornburg”) has contractually agreed to waive fees and reimburse expenses incurred by the Fund so that actual Class I expenses (excluding taxes, interest expenses, 12b-1 distribution and service fees, acquired fund fees and expenses, brokerage commissions, borrowing costs, expenses relating to short sales, and unusual expenses such as contingency fees or litigation costs) do not exceed 0.95%. The agreement to waive fees and reimburse expenses may be terminated by the Fund’s Trustees at any time, but may not be terminated by Thornburg before February 1, 2023, unless Thornburg ceases to be the investment advisor of the Fund prior to that date. Thornburg may recoup amounts waived or reimbursed during the Fund’s fiscal year if actual expenses fall below the expense cap during that same fiscal year.
[24] Up to a 1.00% contingent deferred sales charge (CDSC) is imposed on redemptions of any part or all of a purchase of $1 million or more within 12 months of purchase.
[25] European Union tax reclaim collection fees are considered extraordinary expenses and are excluded from the Fund’s Other Expenses. If such fees were included, the Fund’s Other Expenses for Classes A, I and C would have been 0.31%, 0.33% and 0.32%, respectively.
[26] The figures for Total Annual Fund Operating Expenses in this table have been recalculated to add amounts for “Acquired Fund Fees and Expenses,” in accordance with regulatory rules. Acquired Fund Fees and Expenses vary with changes in the amount of the Fund’s investments in investment companies and other factors. Please see the disclosure under the caption “Explanation of Acquired Fund Fees and Expenses” for a further explanation.
[27] Imposed only on redemptions of Class C shares within 12 months of purchase.
[28] Up to a 1.00% contingent deferred sales charge (CDSC) is imposed on redemptions of any part or all of a purchase of $1 million or more within 12 months of purchase.
[29] These expenses reflect the expenses the Fund will incur to sell securities short and interest expense on borrowed funds. These expenses are required to be treated as a Fund expense for accounting purposes and are not payable to the Fund’s investment advisor.
[30] Thornburg Investment Management, Inc. (“Thornburg”) has contractually agreed to waive fees and reimburse expenses excluding taxes, interest expenses, 12b-1 distribution and service fees, acquired fund fees and expenses, brokerage commissions, borrowing costs, expenses relating to short sales, and unusual expenses such as contingency fees or litigation costs) incurred by the Fund so that actual Class A and Class I expenses do not exceed 1.24% and 0.99%, respectively, not including the effects of expenses relating to the Fund’s short sales, and interest expenses. The agreement to waive fees and reimburse expenses may be terminated by the Fund’s Trustees at any time, but may not be terminated by Thornburg before February 1, 2023 unless Thornburg ceases to be the investment advisor of the Fund prior to that date. Thornburg may recoup amounts waived or reimbursed during the Fund’s fiscal year if, after taking the recoupment into account, the Fund’s actual expenses fall below the expense cap during that same fiscal year.
[31] Up to a 0.50% contingent deferred sales charge (CDSC) is imposed on redemptions of any part or all of a purchase of $1 million or more within 12 months of purchase.
[32] Imposed only on redemptions of Class C and Class C2 shares within 12 months of purchase.
[33] Thornburg Investment Management, Inc. (“Thornburg”) has contractually agreed to waive fees and reimburse expenses incurred by the Fund so that actual Class C2 expenses (excluding taxes, interest expenses, 12b-1 distribution and service fees, acquired fund fees and expenses, brokerage commissions, borrowing costs, expenses relating to short sales, and unusual expenses such as contingency fees or litigation costs) do not exceed 1.24%. The agreement to waive fees and reimburse expenses may be terminated by the Fund’s Trustees at any time, but may not be terminated by Thornburg before February 1, 2023, unless Thornburg ceases to be the investment advisor of the Fund prior to that date. Thornburg may recoup amounts waived or reimbursed during the Fund’s fiscal year if actual expenses fall below the expense cap during that same fiscal year.
[34] Up to a 0.50% contingent deferred sales charge (CDSC) is imposed on redemptions of any part or all of a purchase of $1 million or more within 12 months of purchase.
[35] Imposed only on redemptions of Class C and Class C2 shares within 12 months of purchase.
[36] Thornburg Investment Management, Inc. (“Thornburg”) has contractually agreed to waive fees and reimburse expenses incurred by the Fund so that actual Class C2 and Class I expenses (excluding taxes, interest expenses, 12b-1 distribution and service fees, acquired fund fees and expenses, brokerage commissions, borrowing costs, expenses relating to short sales, and unusual expenses such as contingency fees or litigation costs) do not exceed 1.24% and 0.49%, respectively. The agreement to waive fees and reimburse expenses may be terminated by the Fund’s Trustees at any time, but may not be terminated by Thornburg before February 1, 2023, unless Thornburg ceases to be the investment advisor of the Fund prior to that date. Thornburg may recoup amounts waived or reimbursed during the Fund’s fiscal year if actual expenses fall below the expense cap during that same fiscal year.
[37] Up to a 0.50% contingent deferred sales charge (CDSC) is imposed on redemptions of any part or all of a purchase of $1 million or more within 12 months of purchase.
[38] Thornburg Investment Management, Inc. (“Thornburg”) has contractually agreed to waive fees and reimburse expenses incurred by the Fund so that actual Class A and Class I expenses (excluding taxes, interest expenses, 12b-1 distribution and service fees, acquired fund fees and expenses, brokerage commissions, borrowing costs, expenses relating to short sales, and unusual expenses such as contingency fees or litigation costs) do not exceed 0.50% and 0.30%, respectively. The agreement to waive fees and reimburse expenses may be terminated by the Fund’s Trustees at any time, but may not be terminated by Thornburg before February 1, 2023, unless Thornburg ceases to be the investment advisor of the Fund prior to that date. Thornburg may recoup amounts waived or reimbursed during the Fund’s fiscal year if actual expenses fall below the expense cap during that same fiscal year.
[39] Up to a 1.00% contingent deferred sales charge (CDSC) is imposed on redemptions of any part or all of a purchase of $1 million or more within 12 months of purchase.
[40] Imposed only on redemptions of Class C shares within 12 months of purchase.
[41] Thornburg Investment Management, Inc. (“Thornburg”) has contractually agreed to waive fees and reimburse expenses incurred by the Fund so that actual Class C, and Class I expenses (excluding taxes, interest expenses, 12b-1 distribution and service fees, acquired fund fees and expenses, brokerage commissions, borrowing costs, expenses relating to short sales, and unusual expenses such as contingency fees or litigation costs) do not exceed 1.80%, and 0.60%, respectively. The agreement to waive fees and reimburse expenses may be terminated by the Fund’s Trustees at any time, but may not be terminated by Thornburg before February 1, 2023, unless Thornburg ceases to be the investment advisor of the Fund prior to that date. Thornburg may recoup amounts waived or reimbursed during the Fund’s fiscal year if actual expenses fall below the expense cap during that same fiscal year.
[42] Up to a 0.50% contingent deferred sales charge (CDSC) is imposed on redemptions of any part or all of a purchase of $1 million or more within 12 months of purchase.
[43] Thornburg Investment Management, Inc. (“Thornburg”) has contractually agreed to waive fees and reimburse expenses incurred by the Fund so that actual Class A and Class I expenses (excluding taxes, interest expenses, 12b-1 distribution and service fees, acquired fund fees and expenses, brokerage commissions, borrowing costs, expenses relating to short sales, and unusual expenses such as contingency fees or litigation costs) do not exceed 0.70% and 0.50%, respectively. The agreement to waive fees and reimburse expenses may be terminated by the Fund’s Trustees at any time, but may not be terminated by Thornburg before February 1, 2023, unless Thornburg ceases to be the investment advisor of the Fund prior to that date. Thornburg may recoup amounts waived or reimbursed during the Fund’s fiscal year if actual expenses fall below the expense cap during that same fiscal year.
[44] Up to a 0.50% contingent deferred sales charge (CDSC) is imposed on redemptions of any part or all of a purchase of $1 million or more within 12 months of purchase.
[45] Imposed only on redemptions of Class C and Class C2 shares within 12 months of purchase.
[46] Thornburg Investment Management, Inc. (“Thornburg”) has contractually agreed to waive fees and reimburse expenses incurred by the Fund so that actual Class C2 expenses (excluding taxes, interest expenses, 12b-1 distribution and service fees, acquired fund fees and expenses, brokerage commissions, borrowing costs, expenses relating to short sales, and unusual expenses such as contingency fees or litigation costs) do not exceed 1.24%. The agreement to waive fees and reimburse expenses may be terminated by the Fund’s Trustees at any time, but may not be terminated by Thornburg before February 1, 2023, unless Thornburg ceases to be the investment advisor of the Fund prior to that date. Thornburg may recoup amounts waived or reimbursed during the Fund’s fiscal year if actual expenses fall below the expense cap during that same fiscal year.
[47] Up to a 0.50% contingent deferred sales charge (CDSC) is imposed on redemptions of any part or all of a purchase of $1 million or more within 12 months of purchase.
[48] Thornburg Investment Management, Inc. (“Thornburg”) has contractually agreed to waive fees and reimburse expenses incurred by the Fund so that actual Class A, Class C, Class C2, and Class I expenses (excluding taxes, interest expenses, 12b-1 distribution and service fees, acquired fund fees and expenses, brokerage commissions, borrowing costs, expenses relating to short sales, and unusual expenses such as contingency fees or litigation costs) do not exceed 0.74%, 1.02%, 1.02%, and 0.49%, respectively. The agreement to waive fees and reimburse expenses may be terminated by the Fund’s Trustees at any time, but may not be terminated by Thornburg before February 1, 2023, unless Thornburg ceases to be the investment advisor of the Fund prior to that date. Thornburg may recoup amounts waived or reimbursed during the Fund’s fiscal year if actual expenses fall below the expense cap during that same fiscal year.
[49] Imposed only on redemptions of Class C and Class C2 shares within 12 months of purchase.
[50] Up to a 0.50% contingent deferred sales charge (CDSC) is imposed on redemptions of any part or all of a purchase of $1 million or more within 12 months of purchase.
[51] Thornburg Investment Management, Inc. (“Thornburg”) has contractually agreed to waive fees and reimburse expenses incurred by the Fund so that actual Class D and Class I expenses (excluding taxes, interest expenses, 12b-1 distribution and service fees, acquired fund fees and expenses, brokerage commissions, borrowing costs, expenses relating to short sales, and unusual expenses such as contingency fees or litigation costs) do not exceed 1.24% and 0.67%, respectively. The agreement to waive fees and reimburse expenses may be terminated by the Fund’s Trustees at any time, but may not be terminated by Thornburg before February 1, 2023, unless Thornburg ceases to be the investment advisor of the Fund prior to that date. Thornburg may recoup amounts waived or reimbursed during the Fund’s fiscal year if actual expenses fall below the expense cap during that same fiscal year.
[52] Up to a 0.50% contingent deferred sales charge (CDSC) is imposed on redemptions of any part or all of a purchase of $1 million or more within 12 months of purchase.
[53] Thornburg Investment Management, Inc. (“Thornburg”) has contractually agreed to waive fees and reimburse expenses incurred by the Fund so that actual Class A and Class I expenses (excluding taxes, interest expenses, 12b-1 distribution and service fees, acquired fund fees and expenses, brokerage commissions, borrowing costs, expenses relating to short sales, and unusual expenses such as contingency fees or litigation costs) do not exceed 0.99% and 0.67%, respectively. The agreement to waive fees and reimburse expenses may be terminated by the Fund’s Trustees at any time, but may not be terminated by Thornburg before February 1, 2023, unless Thornburg ceases to be the investment advisor of the Fund prior to that date. Thornburg may recoup amounts waived or reimbursed during the Fund’s fiscal year if actual expenses fall below the expense cap during that same fiscal year.
[54] Up to a 0.50% contingent deferred sales charge (CDSC) is imposed on redemptions of any part or all of a purchase of $1 million or more within 12 months of purchase.
[55] Thornburg Investment Management, Inc. (“Thornburg”) has contractually agreed to waive fees and reimburse expenses incurred by the Fund so that actual Class A, Class C, Class C2, and Class I expenses (excluding taxes, interest expenses, 12b-1 distribution and service fees, acquired fund fees and expenses, brokerage commissions, borrowing costs, expenses relating to short sales, and unusual expenses such as contingency fees or litigation costs) do not exceed 0.77%, 1.14%, 1.14%, and 0.53%. The agreement to waive fees and reimburse expenses may be terminated by the Fund’s Trustees at any time, but may not be terminated by Thornburg before February 1, 2023, unless Thornburg ceases to be the investment advisor of the Fund prior to that date. Thornburg may recoup amounts waived or reimbursed during the Fund’s fiscal year if actual expenses fall below the expense cap during that same fiscal year.
[56] Imposed only on redemptions of Class C and Class C2 shares within 12 months of purchase.
[57] A 0.50% contingent deferred sales charge (CDSC) is imposed on redemptions of any part or all of a purchase of $1 million or more within 12 months of purchase.
[58] Thornburg Investment Management, Inc. (“Thornburg”) has contractually agreed to waive fees and reimburse expenses incurred by the Fund so that actual Class A, Class C, and Class I expenses (excluding taxes, interest expenses, 12b-1 distribution and service fees, acquired fund fees and expenses, brokerage commissions, borrowing costs, expenses relating to short sales, and unusual expenses such as contingency fees or litigation costs) do not exceed 0.81%, 1.28%, and 0.59%, respectively. The agreement to waive fees and reimburse expenses may be terminated by the Fund’s Trustees at any time, but may not be terminated by Thornburg before February 1, 2023, unless Thornburg ceases to be the investment advisor of the Fund prior to that date. Thornburg may recoup amounts waived or reimbursed during the Fund’s fiscal year if actual expenses fall below the expense cap during that same fiscal year.
[59] Imposed only on redemptions of Class C shares within 12 months of purchase.
[60] Thornburg Investment Management, Inc. (“Thornburg”) has contractually agreed to waive fees and reimburse expenses incurred by the Fund so that actual Class R3, Class R4, Class R5, and Class R6 expenses (excluding taxes, interest expenses, 12b-1 distribution and service fees, acquired fund fees and expenses, brokerage commissions, borrowing costs, expenses relating to short sales, and unusual expenses such as contingency fees or litigation costs) do not exceed 1.50%, 1.40%, 0.99%, and 0.85%, respectively. The agreement to waive fees and reimburse expenses may be terminated by the Fund’s Trustees at any time, but may not be terminated by Thornburg before February 1, 2023, unless Thornburg ceases to be the investment advisor of the Fund prior to that date. Thornburg may recoup amounts waived or reimbursed during the Fund’s fiscal year if actual expenses fall below the expense cap during that same fiscal year.
[61] European Union tax reclaim collection fees are considered extraordinary expenses and are excluded from the Fund’s Other Expenses. If such fees were included, the Fund’s Other Expenses for Classes R3, R4, R5, and R6 would have been 0.67%, 0.71%, 0.72% and 0.44%, respectively.
[62] Thornburg Investment Management, Inc. (“Thornburg”) has contractually agreed to waive fees and reimburse expenses incurred by the Fund so that actual Class R3, Class R4, and Class R5 expenses (excluding taxes, interest expenses, 12b-1 distribution and service fees, acquired fund fees and expenses, brokerage commissions, borrowing costs, expenses relating to short sales, and unusual expenses such as contingency fees or litigation costs) do not exceed 1.36%, 1.16%, 0.90%, and 0.70%, respectively. The agreement to waive fees and reimburse expenses may be terminated by the Fund’s Trustees at any time, but may not be terminated by Thornburg before February 1, 2023, unless Thornburg ceases to be the investment advisor of the Fund prior to that date. Thornburg may recoup amounts waived or reimbursed during the Fund’s fiscal year if actual expenses fall below the expense cap during that same fiscal year.
[63] European Union tax reclaim collection fees are considered extraordinary expenses and are excluded from the Fund’s Other Expenses. If such fees were included, the Fund’s Other Expenses for Classes R3, R4, R5, and R6 would have been 0.59 %, 0.58%, 0.47% and 0.16%, respectively.
[64] Thornburg Investment Management, Inc. (“Thornburg”) has contractually agreed to waive fees and reimburse expenses incurred by the Fund so that actual Class R3, Class R4, Class R5 and Class R6 expenses (excluding taxes, interest expenses, 12b-1 distribution and service fees, acquired fund fees and expenses, brokerage commissions, borrowing costs, expenses relating to short sales, and unusual expenses such as contingency fees or litigation costs) do not exceed 1.50%, 1.40%, 0.99%, and 0.89%, respectively. The agreement to waive fees and reimburse expenses may be terminated by the Fund’s Trustees at any time, but may not be terminated by Thornburg before February 1, 2023, unless Thornburg ceases to be the investment advisor of the Fund prior to that date. Thornburg may recoup amounts waived or reimbursed during the Fund’s fiscal year if actual expenses fall below the expense cap during that same fiscal year.
[65] Thornburg Investment Management, Inc. (“Thornburg”) has contractually agreed to waive fees and reimburse expenses incurred by the Fund so that actual Class R5 and Class R6 expenses (excluding taxes, interest expenses, 12b-1 distribution and service fees, acquired fund fees and expenses, brokerage commissions, borrowing costs, expenses relating to short sales, and unusual expenses such as contingency fees or litigation costs) do not exceed 1.04% and 0.94%, respectively. The agreement to waive fees and reimburse expenses may be terminated by the Fund’s Trustees at any time, but may not be terminated by Thornburg before February 1, 2023, unless Thornburg ceases to be the investment advisor of the Fund prior to that date. Thornburg may recoup amounts waived or reimbursed during the Fund’s fiscal year if actual expenses fall below the expense cap during that same fiscal year.
[66] European Union tax reclaim collection fees are considered extraordinary expenses and are excluded from the Fund’s Other Expenses. If such fees were included, the Fund’s Other Expenses for Classes R3, R4, and R5 would have been 0.46%, 0.68% and 0.63%, respectively.
[67] Thornburg Investment Management, Inc. (“Thornburg”) has contractually agreed to waive fees and reimburse expenses incurred by the Fund so that actual Class R3, Class R4 and Class R5 expenses (excluding taxes, interest expenses, 12b-1 distribution and service fees, acquired fund fees and expenses, brokerage commissions, borrowing costs, expenses relating to short sales, and unusual expenses such as contingency fees or litigation costs) do not exceed 1.31%, 1.21%, and 0.95%, respectively. The agreement to waive fees and reimburse expenses may be terminated by the Fund’s Trustees at any time, but may not be terminated by Thornburg before February 1, 2023, unless Thornburg ceases to be the investment advisor of the Fund prior to that date. Thornburg may recoup amounts waived or reimbursed during the Fund’s fiscal year if actual expenses fall below the expense cap during that same fiscal year.
[68] Thornburg Investment Management, Inc. (“Thornburg”) has contractually agreed to waive fees and reimburse expenses incurred by the Fund so that actual Class R3, Class R4 and Class R5 expenses (excluding taxes, interest expenses, 12b-1 distribution and service fees, acquired fund fees and expenses, brokerage commissions, borrowing costs, expenses relating to short sales, and unusual expenses such as contingency fees or litigation costs) do not exceed 1.46%, 1.36%, and 0.95%, respectively. The agreement to waive fees and reimburse expenses may be terminated by the Fund’s Trustees at any time, but may not be terminated by Thornburg before February 1, 2023, unless Thornburg ceases to be the investment advisor of the Fund prior to that date. Thornburg may recoup amounts waived or reimbursed during the Fund’s fiscal year if actual expenses fall below the expense cap during that same fiscal year.
[69] European Union tax reclaim collection fees are considered extraordinary expenses and are excluded from the Fund’s Other Expenses. If such fees were included, the Fund’s Other Expenses for Classes R3, R4, R5, and R6 would have been 0.51%, 0.64%, 0.52% and 0.27%, respectively.
[70] Thornburg Investment Management, Inc. (“Thornburg”) has contractually agreed to waive fees and reimburse expenses incurred by the Fund so that actual Class R3, Class R4, Class R5, and Class R6 expenses (excluding taxes, interest expenses, 12b-1 distribution and service fees, acquired fund fees and expenses, brokerage commissions, borrowing costs, expenses relating to short sales, and unusual expenses such as contingency fees or litigation costs) do not exceed 1.50%, 1.40%, 0.99%, and 0.80% respectively, not including the effects of Acquired Fund Fees and Expenses. The agreement to waive fees and reimburse expenses may be terminated by the Fund’s Trustees at any time, but may not be terminated by Thornburg before February 1, 2023, unless Thornburg ceases to be the investment advisor of the Fund prior to that date. Thornburg may recoup amounts waived or reimbursed during the Fund’s fiscal year if actual expenses fall below the expense cap during that same fiscal year.
[71] The figures for Total Fund Operating Expenses After Fee Waiver/Expense Reimbursement in this table have been recalculated to add amounts for “Acquired Fund Fees and Expenses,” in accordance with regulatory rules. Acquired Fund Fees and Expenses vary with changes in the amount of the Fund’s investments in investment companies and other factors. Please see the disclosure under the caption “Explanation of Acquired Fund Fees and Expenses” for a further explanation.
[72] Thornburg Investment Management, Inc. (“Thornburg”) has contractually agreed to waive fees and reimburse expenses incurred by the Fund so that actual Class R3, Class R4, and Class R5 expenses (excluding taxes, interest expenses, 12b-1 distribution and service fees, acquired fund fees and expenses, brokerage commissions, borrowing costs, expenses relating to short sales, and unusual expenses such as contingency fees or litigation costs) do not exceed 0.99%, 0.99%, and 0.67%, respectively. The agreement to waive fees and reimburse expenses may be terminated by the Fund’s Trustees at any time, but may not be terminated by Thornburg before February 1, 2023, unless Thornburg ceases to be the investment advisor of the Fund prior to that date. Thornburg may recoup amounts waived or reimbursed during the Fund’s fiscal year if actual expenses fall below the expense cap during that same fiscal year.
[73] Thornburg Investment Management, Inc. (“Thornburg”) has contractually agreed to waive fees and reimburse expenses incurred by the Fund so that actual Class R3, Class R4, Class R5, and Class R6 expenses (excluding taxes, interest expenses, 12b-1 distribution and service fees, acquired fund fees and expenses, brokerage commissions, borrowing costs, expenses relating to short sales, and unusual expenses such as contingency fees or litigation costs) do not exceed 0.99%, 0.99%, 0.49%, and 0.42%, respectively. The agreement to waive fees and reimburse expenses may be terminated by the Fund’s Trustees at any time, but may not be terminated by Thornburg before February 1, 2023, unless Thornburg ceases to be the investment advisor of the Fund prior to that date. Thornburg may recoup amounts waived or reimbursed during the Fund’s fiscal year if actual expenses fall below the expense cap during that same fiscal year.
[74] Thornburg Investment Management, Inc. (“Thornburg”) has contractually agreed to waive fees and reimburse expenses incurred by the Fund so that actual Class R3, Class R4, Class R5 and Class R6 expenses (excluding taxes, interest expenses, 12b-1 distribution and service fees, acquired fund fees and expenses, brokerage commissions, borrowing costs, expenses relating to short sales, and unusual expenses such as contingency fees or litigation costs) do not exceed 1.25%, 1.25%, 0.60%, and 0.53%, respectively. The agreement to waive fees and reimburse expenses may be terminated by the Fund’s Trustees at any time, but may not be terminated by Thornburg before February 1, 2023, unless Thornburg ceases to be the investment advisor of the Fund prior to that date. Thornburg may recoup amounts waived or reimbursed during the Fund’s fiscal year if actual expenses fall below the expense cap during that same fiscal year.