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 this Prospectus under the captions “Class A Sales Charge Waivers,” beginning on page 72, and “Appendix A – Sales Charge Waivers Offered by Financial Intermediaries,” beginning on page 104, and in the Statement of Additional Information under the caption “Additional Information Respecting Purchase and Redemption of Shares,” beginning on page 73.

Operating Expenses Caption [Text]

rr_OperatingExpensesCaption

Annual Fund Operating Expenses

Portfolio Turnover [Heading]

rr_PortfolioTurnoverHeading

Portfolio Turnover

Portfolio Turnover, Rate

rr_PortfolioTurnoverRate

33.60%

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 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 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. 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 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. Municipal leases held by the Fund may be subject to non-appropriation provisions which permit governmental issuers to discontinue payments to the Fund under the 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.

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.

Additional information about Fund investments, investment strategies and risks of investing in the Fund appears beginning on page 51.

Risk Not Insured Depository Institution [Text]

rr_RiskNotInsuredDepositoryInstitution

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.

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, 2019. Updated performance information may be obtained on the Thornburg website at www.thornburg.com or by calling 1-800-847-0200.

Performance Additional Market Index [Text]

rr_PerformanceAdditionalMarketIndex

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.

Performance Availability Website Address [Text]

rr_PerformanceAvailabilityWebSiteAddress

www.thornburg.com

Bar Chart [Heading]

rr_BarChartHeading

Annual Total Returns – Class A Shares

Bar Chart Closing [Text Block]

rr_BarChartClosingTextBlock

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 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 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.

Trading Symbol

dei_TradingSymbol

TLMAX

Maximum Deferred Sales Charge (as a percentage)

rr_MaximumDeferredSalesChargeOverOther

none

^[1]

Distribution and Service (12b-1) Fees

rr_DistributionAndService12b1FeesOverAssets

0.20%

Expenses (as a percentage of Assets)

rr_ExpensesOverAssets

0.99%

Net Expenses (as a percentage of Assets)

rr_NetExpensesOverAssets

0.70%

Expense Example, with Redemption, 3 Years

rr_ExpenseExampleYear03

505

Expense Example, with Redemption, 10 Years

rr_ExpenseExampleYear10

$ 1,385

Annual Return 2015

rr_AnnualReturn2015

0.14%

Annual Return 2017

rr_AnnualReturn2017

0.89%

Annual Return 2019

rr_AnnualReturn2019

1.91%

Highest Quarterly Return, Date

rr_BarChartHighestQuarterlyReturnDate

Mar. 31, 2019

Lowest Quarterly Return, Label

rr_LowestQuarterlyReturnLabel

Lowest Quarterly Results

Lowest Quarterly Return

rr_BarChartLowestQuarterlyReturn

(0.36%)

5 Years

rr_AverageAnnualReturnYear05

0.31%

Inception Date

rr_AverageAnnualReturnInceptionDate

Dec. 30, 2013

Prospectus [Line Items]

rr_ProspectusLineItems

5 Years

rr_AverageAnnualReturnYear05

0.31%

1 Year

rr_AverageAnnualReturnYear01

0.29%

Since Inception

rr_AverageAnnualReturnSinceInception

0.38%

Prospectus [Line Items]

rr_ProspectusLineItems

5 Years

rr_AverageAnnualReturnYear05

1.34%

Trading Symbol

dei_TradingSymbol

TLMIX

Maximum Deferred Sales Charge (as a percentage)

rr_MaximumDeferredSalesChargeOverOther

none

Distribution and Service (12b-1) Fees

rr_DistributionAndService12b1FeesOverAssets

none

Expenses (as a percentage of Assets)

rr_ExpensesOverAssets

0.64%

Net Expenses (as a percentage of Assets)

rr_NetExpensesOverAssets

0.50%

Expense Example, with Redemption, 3 Years

rr_ExpenseExampleYear03

191

Expense Example, with Redemption, 10 Years

rr_ExpenseExampleYear10

$ 785

5 Years

rr_AverageAnnualReturnYear05

0.96%

Inception Date

rr_AverageAnnualReturnInceptionDate

Dec. 30, 2013

Prospectus [Line Items]

rr_ProspectusLineItems

5 Years

rr_AverageAnnualReturnYear05

1.34%

Risk/Return [Heading]

rr_RiskReturnHeading

Fund Summary

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.

Expense [Heading]

rr_ExpenseHeading

Fees and Expenses of the Fund

Shareholder Fees Caption [Text]

rr_ShareholderFeesCaption

Shareholder Fees

Portfolio Turnover [Heading]

rr_PortfolioTurnoverHeading

Portfolio Turnover

Portfolio Turnover, Rate

rr_PortfolioTurnoverRate

21.22%

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:

Strategy [Heading]

rr_StrategyHeading

Principal Investment Strategies

Risk [Heading]

rr_RiskHeading

Principal Investment Risks

Risk Lose Money [Text]

rr_RiskLoseMoney

Accordingly, the loss of money is a risk of investing in the Fund.

Bar Chart and Performance Table [Heading]

rr_BarChartAndPerformanceTableHeading

Past Performance of the Fund

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 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 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.

Performance Table Heading

rr_PerformanceTableHeading

Average Annual Total Returns

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. The after-tax returns shown relate only to Class A shares, and after-tax returns for other share classes will vary.

Prospectus [Line Items]

rr_ProspectusLineItems

Maximum Sales Charge Imposed on Purchases (as a percentage of Offering Price)

rr_MaximumSalesChargeImposedOnPurchasesOverOfferingPrice

2.25%

Management Fees (as a percentage of Assets)

rr_ManagementFeesOverAssets

0.27%

Other Expenses (as a percentage of Assets):

rr_OtherExpensesOverAssets

0.17%

Expense Example, with Redemption, 1 Year

rr_ExpenseExampleYear01

$ 294

Expense Example, with Redemption, 5 Years

rr_ExpenseExampleYear05

601

Annual Return 2010

rr_AnnualReturn2010

3.00%

Annual Return 2012

rr_AnnualReturn2012

3.07%

Annual Return 2014

rr_AnnualReturn2014

2.99%

Annual Return 2016

rr_AnnualReturn2016

(0.69%)

Annual Return 2018

rr_AnnualReturn2018

0.88%

Highest Quarterly Return, Label

rr_HighestQuarterlyReturnLabel

Highest Quarterly Results

Highest Quarterly Return

rr_BarChartHighestQuarterlyReturn

4.49%

Lowest Quarterly Return, Date

rr_BarChartLowestQuarterlyReturnDate

Dec. 31, 2016

1 Year

rr_AverageAnnualReturnYear01

1.45%

10 Years

rr_AverageAnnualReturnYear10

2.08%

Prospectus [Line Items]

rr_ProspectusLineItems

5 Years

rr_AverageAnnualReturnYear05

1.09%

1 Year

rr_AverageAnnualReturnYear01

1.59%

10 Years

rr_AverageAnnualReturnYear10

2.04%

Prospectus [Line Items]

rr_ProspectusLineItems

5 Years

rr_AverageAnnualReturnYear05

2.36%

Trading Symbol

dei_TradingSymbol

LTMCX

Maximum Deferred Sales Charge (as a percentage)

rr_MaximumDeferredSalesChargeOverOther

0.50%

^[4]

Distribution and Service (12b-1) Fees

rr_DistributionAndService12b1FeesOverAssets

0.50%

Expenses (as a percentage of Assets)

rr_ExpensesOverAssets

0.94%

Expense Example, with Redemption, 3 Years

rr_ExpenseExampleYear03

300

Expense Example, with Redemption, 10 Years

rr_ExpenseExampleYear10

1,155

Expense Example, No Redemption, 3 Years

rr_ExpenseExampleNoRedemptionYear03

300

Expense Example, No Redemption, 10 Years

rr_ExpenseExampleNoRedemptionYear10

$ 1,155

5 Years

rr_AverageAnnualReturnYear05

1.30%

1 Year

rr_AverageAnnualReturnYear01

5.28%

10 Years

rr_AverageAnnualReturnYear10

2.82%

Prospectus [Line Items]

rr_ProspectusLineItems

Maximum Sales Charge Imposed on Purchases (as a percentage of Offering Price)

rr_MaximumSalesChargeImposedOnPurchasesOverOfferingPrice

none

^[5]

Management Fees (as a percentage of Assets)

rr_ManagementFeesOverAssets

0.27%

Other Expenses (as a percentage of Assets):

rr_OtherExpensesOverAssets

0.17%

^[6]

Expense Example, with Redemption, 1 Year

rr_ExpenseExampleYear01

$ 176

Expense Example, with Redemption, 5 Years

rr_ExpenseExampleYear05

601

Expense Example, No Redemption, 1 Year

rr_ExpenseExampleNoRedemptionYear01

111

Expense Example, No Redemption, 5 Years

rr_ExpenseExampleNoRedemptionYear05

601

Trading Symbol

dei_TradingSymbol

LTMIX

Maximum Deferred Sales Charge (as a percentage)

rr_MaximumDeferredSalesChargeOverOther

none

Distribution and Service (12b-1) Fees

rr_DistributionAndService12b1FeesOverAssets

none

Expenses (as a percentage of Assets)

rr_ExpensesOverAssets

0.45%

Expense Example, with Redemption, 3 Years

rr_ExpenseExampleYear03

144

Expense Example, with Redemption, 10 Years

rr_ExpenseExampleYear10

$ 567

5 Years

rr_AverageAnnualReturnYear05

1.84%

1 Year

rr_AverageAnnualReturnYear01

5.28%

10 Years

rr_AverageAnnualReturnYear10

2.82%

Prospectus [Line Items]

rr_ProspectusLineItems

Objective [Heading]

rr_ObjectiveHeading

Investment Goal

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 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 this Prospectus under the captions “Class A Sales Charge Waivers,” beginning on page 72, and “Appendix A – Sales Charge Waivers Offered by Financial Intermediaries,” beginning on page 104, and in the Statement of Additional Information under the caption “Additional Information Respecting Purchase and Redemption of Shares,” beginning on page 73

Operating Expenses Caption [Text]

rr_OperatingExpensesCaption

Annual Fund Operating Expenses

Portfolio Turnover [Heading]

rr_PortfolioTurnoverHeading

Portfolio Turnover

Portfolio Turnover, Rate

rr_PortfolioTurnoverRate

15.88%

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:

Strategy [Heading]

rr_StrategyHeading

Principal Investment Strategies

Risk [Heading]

rr_RiskHeading

Principal Investment Risks

Risk Lose Money [Text]

rr_RiskLoseMoney

Accordingly, the loss of money is a risk of investing in the Fund.

Bar Chart and Performance Table [Heading]

rr_BarChartAndPerformanceTableHeading

Past Performance of the Fund

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 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 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.

Performance Table Heading

rr_PerformanceTableHeading

Average Annual Total Returns

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 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.

Prospectus [Line Items]

rr_ProspectusLineItems

Maximum Sales Charge Imposed on Purchases (as a percentage of Offering Price)

rr_MaximumSalesChargeImposedOnPurchasesOverOfferingPrice

2.00%

Management Fees (as a percentage of Assets)

rr_ManagementFeesOverAssets

0.46%

Other Expenses (as a percentage of Assets):

rr_OtherExpensesOverAssets

0.18%

Fee Waiver or Reimbursement

rr_FeeWaiverOrReimbursementOverAssets

(0.12%)

Expense Example, with Redemption, 1 Year

rr_ExpenseExampleYear01

$ 277

Expense Example, with Redemption, 5 Years

rr_ExpenseExampleYear05

672

Annual Return 2010

rr_AnnualReturn2010

2.53%

Annual Return 2012

rr_AnnualReturn2012

5.99%

Annual Return 2014

rr_AnnualReturn2014

6.55%

Annual Return 2016

rr_AnnualReturn2016

(0.50%)

Annual Return 2018

rr_AnnualReturn2018

0.56%

Highest Quarterly Return, Label

rr_HighestQuarterlyReturnLabel

Highest Quarterly Results

Highest Quarterly Return

rr_BarChartHighestQuarterlyReturn

6.76%

Lowest Quarterly Return, Date

rr_BarChartLowestQuarterlyReturnDate

Dec. 31, 2010

1 Year

rr_AverageAnnualReturnYear01

3.55%

10 Years

rr_AverageAnnualReturnYear10

3.21%

Prospectus [Line Items]

rr_ProspectusLineItems

5 Years

rr_AverageAnnualReturnYear05

1.85%

1 Year

rr_AverageAnnualReturnYear01

3.11%

10 Years

rr_AverageAnnualReturnYear10

3.08%

Prospectus [Line Items]

rr_ProspectusLineItems

5 Years

rr_AverageAnnualReturnYear05

3.21%

Trading Symbol

dei_TradingSymbol

THMCX

Maximum Deferred Sales Charge (as a percentage)

rr_MaximumDeferredSalesChargeOverOther

0.60%

^[9]

Distribution and Service (12b-1) Fees

rr_DistributionAndService12b1FeesOverAssets

0.60%

Expenses (as a percentage of Assets)

rr_ExpensesOverAssets

1.26%

^[8]

Net Expenses (as a percentage of Assets)

rr_NetExpensesOverAssets

1.14%

Expense Example, with Redemption, 3 Years

rr_ExpenseExampleYear03

388

Expense Example, with Redemption, 10 Years

rr_ExpenseExampleYear10

1,512

Expense Example, No Redemption, 3 Years

rr_ExpenseExampleNoRedemptionYear03

388

Expense Example, No Redemption, 10 Years

rr_ExpenseExampleNoRedemptionYear10

$ 1,512

5 Years

rr_AverageAnnualReturnYear05

1.92%

1 Year

rr_AverageAnnualReturnYear01

7.01%

10 Years

rr_AverageAnnualReturnYear10

3.98%

Prospectus [Line Items]

rr_ProspectusLineItems

Maximum Sales Charge Imposed on Purchases (as a percentage of Offering Price)

rr_MaximumSalesChargeImposedOnPurchasesOverOfferingPrice

none

^[10]

Management Fees (as a percentage of Assets)

rr_ManagementFeesOverAssets

0.46%

Other Expenses (as a percentage of Assets):

rr_OtherExpensesOverAssets

0.20%

^[11]

Fee Waiver or Reimbursement

rr_FeeWaiverOrReimbursementOverAssets

(0.17%)

Expense Example, with Redemption, 1 Year

rr_ExpenseExampleYear01

$ 181

Expense Example, with Redemption, 5 Years

rr_ExpenseExampleYear05

702

Expense Example, No Redemption, 1 Year

rr_ExpenseExampleNoRedemptionYear01

116

Expense Example, No Redemption, 5 Years

rr_ExpenseExampleNoRedemptionYear05

702

Trading Symbol

dei_TradingSymbol

THMIX

Maximum Deferred Sales Charge (as a percentage)

rr_MaximumDeferredSalesChargeOverOther

none

Distribution and Service (12b-1) Fees

rr_DistributionAndService12b1FeesOverAssets

none

Expenses (as a percentage of Assets)

rr_ExpensesOverAssets

0.65%

^[8]

Net Expenses (as a percentage of Assets)

rr_NetExpensesOverAssets

0.53%

Expense Example, with Redemption, 3 Years

rr_ExpenseExampleYear03

196

Expense Example, with Redemption, 10 Years

rr_ExpenseExampleYear10

$ 799

5 Years

rr_AverageAnnualReturnYear05

2.54%

1 Year

rr_AverageAnnualReturnYear01

7.01%

10 Years

rr_AverageAnnualReturnYear10

3.98%

Prospectus [Line Items]

rr_ProspectusLineItems

Objective [Heading]

rr_ObjectiveHeading

Investment Goal

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 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 this Prospectus under the captions “Class A Sales Charge Waivers,” beginning on page 72, and “Appendix A – Sales Charge Waivers Offered by Financial Intermediaries,” beginning on page 104, and in the Statement of Additional Information under the caption “Additional Information Respecting Purchase and Redemption of Shares,” beginning on page 73.

Operating Expenses Caption [Text]

rr_OperatingExpensesCaption

Annual Fund Operating Expenses

Portfolio Turnover [Heading]

rr_PortfolioTurnoverHeading

Portfolio Turnover

Portfolio Turnover, Rate

rr_PortfolioTurnoverRate

17.86%

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:

Strategy [Heading]

rr_StrategyHeading

Principal Investment Strategies

Risk [Heading]

rr_RiskHeading

Principal Investment Risks

Risk Lose Money [Text]

rr_RiskLoseMoney

Accordingly, the loss of money is a risk of investing in the Fund.

Bar Chart and Performance Table [Heading]

rr_BarChartAndPerformanceTableHeading

Past Performance of the Fund

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 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 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.

Performance Table Heading

rr_PerformanceTableHeading

Average Annual Total Returns

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. The after-tax returns shown relate only to Class A shares, and after-tax returns for other share classes will vary.

Prospectus [Line Items]

rr_ProspectusLineItems

Maximum Sales Charge Imposed on Purchases (as a percentage of Offering Price)

rr_MaximumSalesChargeImposedOnPurchasesOverOfferingPrice

2.25%

Management Fees (as a percentage of Assets)

rr_ManagementFeesOverAssets

0.50%

Other Expenses (as a percentage of Assets):

rr_OtherExpensesOverAssets

0.18%

Fee Waiver or Reimbursement

rr_FeeWaiverOrReimbursementOverAssets

(0.19%)

^[13]

Expense Example, with Redemption, 1 Year

rr_ExpenseExampleYear01

$ 299

Expense Example, with Redemption, 5 Years

rr_ExpenseExampleYear05

710

Annual Return 2010

rr_AnnualReturn2010

3.26%

Annual Return 2012

rr_AnnualReturn2012

3.44%

Annual Return 2014

rr_AnnualReturn2014

3.86%

Annual Return 2016

rr_AnnualReturn2016

(0.99%)

Annual Return 2018

rr_AnnualReturn2018

0.52%

Highest Quarterly Return, Label

rr_HighestQuarterlyReturnLabel

Highest Quarterly Results

Highest Quarterly Return

rr_BarChartHighestQuarterlyReturn

4.55%

Lowest Quarterly Return, Date

rr_BarChartLowestQuarterlyReturnDate

Dec. 31, 2016

1 Year

rr_AverageAnnualReturnYear01

0.88%

10 Years

rr_AverageAnnualReturnYear10

2.14%

Prospectus [Line Items]

rr_ProspectusLineItems

5 Years

rr_AverageAnnualReturnYear05

0.81%

1 Year

rr_AverageAnnualReturnYear01

1.15%

10 Years

rr_AverageAnnualReturnYear10

2.07%

Prospectus [Line Items]

rr_ProspectusLineItems

5 Years

rr_AverageAnnualReturnYear05

2.36%

Trading Symbol

dei_TradingSymbol

LTCCX

Maximum Deferred Sales Charge (as a percentage)

rr_MaximumDeferredSalesChargeOverOther

0.50%

^[14]

Distribution and Service (12b-1) Fees

rr_DistributionAndService12b1FeesOverAssets

0.50%

Expenses (as a percentage of Assets)

rr_ExpensesOverAssets

1.21%

Net Expenses (as a percentage of Assets)

rr_NetExpensesOverAssets

1.02%

Expense Example, with Redemption, 3 Years

rr_ExpenseExampleYear03

365

Expense Example, with Redemption, 10 Years

rr_ExpenseExampleYear10

1,449

Expense Example, No Redemption, 3 Years

rr_ExpenseExampleNoRedemptionYear03

365

Expense Example, No Redemption, 10 Years

rr_ExpenseExampleNoRedemptionYear10

$ 1,449

5 Years

rr_AverageAnnualReturnYear05

1.00%

1 Year

rr_AverageAnnualReturnYear01

5.28%

10 Years

rr_AverageAnnualReturnYear10

2.82%

Prospectus [Line Items]

rr_ProspectusLineItems

Maximum Sales Charge Imposed on Purchases (as a percentage of Offering Price)

rr_MaximumSalesChargeImposedOnPurchasesOverOfferingPrice

none

^[15]

Management Fees (as a percentage of Assets)

rr_ManagementFeesOverAssets

0.50%

Other Expenses (as a percentage of Assets):

rr_OtherExpensesOverAssets

0.21%

^[16]

Fee Waiver or Reimbursement

rr_FeeWaiverOrReimbursementOverAssets

(0.34%)

^[13]

Expense Example, with Redemption, 1 Year

rr_ExpenseExampleYear01

$ 169

Expense Example, with Redemption, 5 Years

rr_ExpenseExampleYear05

712

Expense Example, No Redemption, 1 Year

rr_ExpenseExampleNoRedemptionYear01

104

Expense Example, No Redemption, 5 Years

rr_ExpenseExampleNoRedemptionYear05

712

Trading Symbol

dei_TradingSymbol

LTCIX

Maximum Deferred Sales Charge (as a percentage)

rr_MaximumDeferredSalesChargeOverOther

none

Distribution and Service (12b-1) Fees

rr_DistributionAndService12b1FeesOverAssets

none

Expenses (as a percentage of Assets)

rr_ExpensesOverAssets

0.68%

Net Expenses (as a percentage of Assets)

rr_NetExpensesOverAssets

0.49%

Expense Example, with Redemption, 3 Years

rr_ExpenseExampleYear03

198

Expense Example, with Redemption, 10 Years

rr_ExpenseExampleYear10

$ 829

5 Years

rr_AverageAnnualReturnYear05

1.55%

1 Year

rr_AverageAnnualReturnYear01

5.28%

10 Years

rr_AverageAnnualReturnYear10

2.82%

Prospectus [Line Items]

rr_ProspectusLineItems

Objective [Heading]

rr_ObjectiveHeading

Investment Goal

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 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 this Prospectus under the captions “Class A Sales Charge Waivers,” beginning on page 72, and “Appendix A – Sales Charge Waivers Offered by Financial Intermediaries,” beginning on page 104, and in the Statement of Additional Information under the caption “Additional Information Respecting Purchase and Redemption of Shares,” beginning on page 73.

Operating Expenses Caption [Text]

rr_OperatingExpensesCaption

Annual Fund Operating Expenses

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 29.37% of the average value of its portfolio.

Expense Example [Heading]

rr_ExpenseExampleHeading

Example

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 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.

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.

Additional information about Fund investments, investment strategies, and risks of investing in the Fund appears below beginning on page 51.

Risk Not Insured Depository Institution [Text]

rr_RiskNotInsuredDepositoryInstitution

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.

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 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, 2019. No performance information for Class C2 shares is provided because Class C2 shares have not been in operation for a full calendar year. Updated performance information may be obtained on the Thornburg website at www.thornburg.com or by calling 1-800-847-0200.

Performance Additional Market Index [Text]

rr_PerformanceAdditionalMarketIndex

The average annual total return figures compare Class A, Class C and Class I share performance to the Bloomberg Barclays US Government Intermediate Total Return Index Value Unhedged, a broad measure of market performance.

Performance Availability Website Address [Text]

rr_PerformanceAvailabilityWebSiteAddress

www.thornburg.com

Bar Chart [Heading]

rr_BarChartHeading

Annual Total Returns – Class A Shares

Bar Chart Closing [Text Block]

rr_BarChartClosingTextBlock

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 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 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.

Trading Symbol

dei_TradingSymbol

LTUSX

Maximum Deferred Sales Charge (as a percentage)

rr_MaximumDeferredSalesChargeOverOther

none

^[17]

Distribution and Service (12b-1) Fees

rr_DistributionAndService12b1FeesOverAssets

0.25%

Expenses (as a percentage of Assets)

rr_ExpensesOverAssets

0.90%

Expense Example, with Redemption, 3 Years

rr_ExpenseExampleYear03

506

Expense Example, with Redemption, 10 Years

rr_ExpenseExampleYear10

$ 1,308

Annual Return 2011

rr_AnnualReturn2011

3.73%

Annual Return 2013

rr_AnnualReturn2013

(1.87%)

Annual Return 2015

rr_AnnualReturn2015

0.34%

Annual Return 2017

rr_AnnualReturn2017

0.60%

Annual Return 2019

rr_AnnualReturn2019

3.61%

Highest Quarterly Return, Date

rr_BarChartHighestQuarterlyReturnDate

Jun. 30, 2010

Lowest Quarterly Return, Label

rr_LowestQuarterlyReturnLabel

Lowest Quarterly Results

Lowest Quarterly Return

rr_BarChartLowestQuarterlyReturn

(1.55%)

5 Years

rr_AverageAnnualReturnYear05

0.78%

1 Year

rr_AverageAnnualReturnYear01

0.59%

10 Years

rr_AverageAnnualReturnYear10

0.56%

Prospectus [Line Items]

rr_ProspectusLineItems

5 Years

rr_AverageAnnualReturnYear05

0.30%

1 Year

rr_AverageAnnualReturnYear01

5.20%

10 Years

rr_AverageAnnualReturnYear10

2.38%

Prospectus [Line Items]

rr_ProspectusLineItems

Maximum Sales Charge Imposed on Purchases (as a percentage of Offering Price)

rr_MaximumSalesChargeImposedOnPurchasesOverOfferingPrice

none

Management Fees (as a percentage of Assets)

rr_ManagementFeesOverAssets

0.38%

Other Expenses (as a percentage of Assets):

rr_OtherExpensesOverAssets

0.36%

Expense Example, with Redemption, 1 Year

rr_ExpenseExampleYear01

$ 176

Expense Example, with Redemption, 5 Years

rr_ExpenseExampleYear05

681

Expense Example, No Redemption, 1 Year

rr_ExpenseExampleNoRedemptionYear01

126

Expense Example, No Redemption, 5 Years

rr_ExpenseExampleNoRedemptionYear05

681

1 Year

rr_AverageAnnualReturnYear01

2.77%

10 Years

rr_AverageAnnualReturnYear10

1.29%

Prospectus [Line Items]

rr_ProspectusLineItems

5 Years

rr_AverageAnnualReturnYear05

1.99%

Trading Symbol

dei_TradingSymbol

LTUQX

Maximum Deferred Sales Charge (as a percentage)

rr_MaximumDeferredSalesChargeOverOther

0.65%

^[18],[19]

Distribution and Service (12b-1) Fees

rr_DistributionAndService12b1FeesOverAssets

0.65%

Expenses (as a percentage of Assets)

rr_ExpensesOverAssets

1.39%

Expense Example, with Redemption, 3 Years

rr_ExpenseExampleYear03

440

Expense Example, with Redemption, 10 Years

rr_ExpenseExampleYear10

1,669

Expense Example, No Redemption, 3 Years

rr_ExpenseExampleNoRedemptionYear03

440

Expense Example, No Redemption, 10 Years

rr_ExpenseExampleNoRedemptionYear10

$ 1,669

Prospectus [Line Items]

rr_ProspectusLineItems

Maximum Sales Charge Imposed on Purchases (as a percentage of Offering Price)

rr_MaximumSalesChargeImposedOnPurchasesOverOfferingPrice

none

Management Fees (as a percentage of Assets)

rr_ManagementFeesOverAssets

0.38%

Other Expenses (as a percentage of Assets):

rr_OtherExpensesOverAssets

0.24%

Expense Example, with Redemption, 1 Year

rr_ExpenseExampleYear01

$ 63

Expense Example, with Redemption, 5 Years

rr_ExpenseExampleYear05

346

1 Year

rr_AverageAnnualReturnYear01

3.91%

10 Years

rr_AverageAnnualReturnYear10

1.91%

Prospectus [Line Items]

rr_ProspectusLineItems

5 Years

rr_AverageAnnualReturnYear05

1.99%

Risk/Return [Heading]

rr_RiskReturnHeading

Fund Summary

Objective, Primary [Text Block]

rr_ObjectivePrimaryTextBlock

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

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 this Prospectus under the captions “Class A Sales Charge Waivers,” beginning on page 72, and “Appendix A – Sales Charge Waivers Offered by Financial Intermediaries,” beginning on page 104, and in the Statement of Additional Information under the caption “Additional Information Respecting Purchase and Redemption of Shares,” beginning on page 73.

Operating Expenses Caption [Text]

rr_OperatingExpensesCaption

Annual Fund Operating Expenses

Portfolio Turnover [Heading]

rr_PortfolioTurnoverHeading

Portfolio Turnover

Portfolio Turnover, Rate

rr_PortfolioTurnoverRate

79.59%

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 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.

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.

Additional information about Fund investments, investment strategies and risks of investing in the Fund appears beginning on page 51.

Risk Not Insured Depository Institution [Text]

rr_RiskNotInsuredDepositoryInstitution

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.

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, 2019. Updated performance information may be obtained on the Thornburg website at www.thornburg.com or by calling 1-800-847-0200.

The ICE BofAML U.S. Treasury Bill Index replaced the Bloomberg Barclays US Aggregate 1-3 Year Total Return Index Value Unhedged USD as the Fund’s benchmark index on September 30, 2020. This change was approved by the Fund’s Trustees because the new index more closely aligns to the Fund’s investment strategies. Information on both indexes will be shown for at least a one-year transition period. In the future, however, only the ICE BofAML U.S. Treasury Bill Index will be shown.

Performance Additional Market Index [Text]

rr_PerformanceAdditionalMarketIndex

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.

Performance Availability Website Address [Text]

rr_PerformanceAvailabilityWebSiteAddress

www.thornburg.com

Bar Chart [Heading]

rr_BarChartHeading

Annual Total Returns – Class A Shares

Bar Chart Closing [Text Block]

rr_BarChartClosingTextBlock

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 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 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.

Trading Symbol

dei_TradingSymbol

TLDAX

Maximum Deferred Sales Charge (as a percentage)

rr_MaximumDeferredSalesChargeOverOther

none

^[21]

Distribution and Service (12b-1) Fees

rr_DistributionAndService12b1FeesOverAssets

0.20%

Expenses (as a percentage of Assets)

rr_ExpensesOverAssets

1.50%

Net Expenses (as a percentage of Assets)

rr_NetExpensesOverAssets

0.50%

Expense Example, with Redemption, 3 Years

rr_ExpenseExampleYear03

592

Expense Example, with Redemption, 10 Years

rr_ExpenseExampleYear10

$ 1,891

Annual Return 2015

rr_AnnualReturn2015

0.28%

Annual Return 2017

rr_AnnualReturn2017

1.31%

Annual Return 2019

rr_AnnualReturn2019

3.74%

Highest Quarterly Return, Date

rr_BarChartHighestQuarterlyReturnDate

Mar. 31, 2019

Lowest Quarterly Return, Label

rr_LowestQuarterlyReturnLabel

Lowest Quarterly Results

Lowest Quarterly Return

rr_BarChartLowestQuarterlyReturn

(0.37%)

5 Years

rr_AverageAnnualReturnYear05

1.23%

Inception Date

rr_AverageAnnualReturnInceptionDate

Dec. 30, 2013

Prospectus [Line Items]

rr_ProspectusLineItems

5 Years

rr_AverageAnnualReturnYear05

0.57%

1 Year

rr_AverageAnnualReturnYear01

0.84%

Since Inception

rr_AverageAnnualReturnSinceInception

0.68%

Prospectus [Line Items]

rr_ProspectusLineItems

5 Years

rr_AverageAnnualReturnYear05

1.10%

1 Year

rr_AverageAnnualReturnYear01

4.04%

Since Inception

rr_AverageAnnualReturnSinceInception

1.54%

Prospectus [Line Items]

rr_ProspectusLineItems

Maximum Sales Charge Imposed on Purchases (as a percentage of Offering Price)

rr_MaximumSalesChargeImposedOnPurchasesOverOfferingPrice

none

Management Fees (as a percentage of Assets)

rr_ManagementFeesOverAssets

0.25%

Other Expenses (as a percentage of Assets):

rr_OtherExpensesOverAssets

0.54%

Fee Waiver or Reimbursement

rr_FeeWaiverOrReimbursementOverAssets

(0.49%)

^[22]

Expense Example, with Redemption, 1 Year

rr_ExpenseExampleYear01

$ 31

Expense Example, with Redemption, 5 Years

rr_ExpenseExampleYear05

390

1 Year

rr_AverageAnnualReturnYear01

3.86%

Since Inception

rr_AverageAnnualReturnSinceInception

1.81%

1 Year

rr_AverageAnnualReturnYear01

2.35%

Since Inception

rr_AverageAnnualReturnSinceInception

0.92%

Prospectus [Line Items]

rr_ProspectusLineItems

5 Years

rr_AverageAnnualReturnYear05

1.69%

Risk/Return [Heading]

rr_RiskReturnHeading

Fund Summary

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.

Expense [Heading]

rr_ExpenseHeading

Fees and Expenses of the Fund

Shareholder Fees Caption [Text]

rr_ShareholderFeesCaption

Shareholder Fees

Fee Waiver or Reimbursement over Assets, Date of Termination

rr_FeeWaiverOrReimbursementOverAssetsDateOfTermination

September 30, 2021

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 43.22% of the average value of its portfolio.

Expense Example [Heading]

rr_ExpenseExampleHeading

Example

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 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.

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.

Additional information about Fund investments, investment strategies, and risks of investing in the Fund appears below beginning on page 51.

Risk Not Insured Depository Institution [Text]

rr_RiskNotInsuredDepositoryInstitution

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.

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 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, 2019. No performance information for Class C2 shares is provided because Class C2 shares have not been in operation for a full calendar year. Updated performance information may be obtained on the Thornburg website at www.thornburg.com or by calling 1-800-847-0200.

Performance Additional Market Index [Text]

rr_PerformanceAdditionalMarketIndex

The average annual total return figures compare Class A, Class C and Class I share performance to the Bloomberg Barclays Intermediate US Government/Credit Total Return Index Value Unhedged, a broad measure of market performance.

Performance Availability Website Address [Text]

rr_PerformanceAvailabilityWebSiteAddress

www.thornburg.com

Bar Chart [Heading]

rr_BarChartHeading

Annual Total Returns – Class A Shares

Bar Chart Closing [Text Block]

rr_BarChartClosingTextBlock

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 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 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.

Trading Symbol

dei_TradingSymbol

THIFX

Maximum Deferred Sales Charge (as a percentage)

rr_MaximumDeferredSalesChargeOverOther

none

^[23]

Distribution and Service (12b-1) Fees

rr_DistributionAndService12b1FeesOverAssets

0.25%

Expenses (as a percentage of Assets)

rr_ExpensesOverAssets

0.81%

Net Expenses (as a percentage of Assets)

rr_NetExpensesOverAssets

0.81%

Expense Example, with Redemption, 3 Years

rr_ExpenseExampleYear03

478

Expense Example, with Redemption, 10 Years

rr_ExpenseExampleYear10

$ 1,204

Annual Return 2011

rr_AnnualReturn2011

5.08%

Annual Return 2013

rr_AnnualReturn2013

(0.17%)

Annual Return 2015

rr_AnnualReturn2015

0.47%

Annual Return 2017

rr_AnnualReturn2017

2.27%

Annual Return 2019

rr_AnnualReturn2019

5.37%

Highest Quarterly Return, Date

rr_BarChartHighestQuarterlyReturnDate

Jun. 30, 2009

Lowest Quarterly Return, Label

rr_LowestQuarterlyReturnLabel

Lowest Quarterly Results

Lowest Quarterly Return

rr_BarChartLowestQuarterlyReturn

(2.06%)

5 Years

rr_AverageAnnualReturnYear05

1.96%

1 Year

rr_AverageAnnualReturnYear01

1.76%

10 Years

rr_AverageAnnualReturnYear10

2.01%

Prospectus [Line Items]

rr_ProspectusLineItems

5 Years

rr_AverageAnnualReturnYear05

1.08%

1 Year

rr_AverageAnnualReturnYear01

6.80%

10 Years

rr_AverageAnnualReturnYear10

3.05%

Prospectus [Line Items]

rr_ProspectusLineItems

Maximum Sales Charge Imposed on Purchases (as a percentage of Offering Price)

rr_MaximumSalesChargeImposedOnPurchasesOverOfferingPrice

none

Management Fees (as a percentage of Assets)

rr_ManagementFeesOverAssets

0.33%

Other Expenses (as a percentage of Assets):

rr_OtherExpensesOverAssets

0.19%

Fee Waiver or Reimbursement

rr_FeeWaiverOrReimbursementOverAssets

none

^[24]

Expense Example, with Redemption, 1 Year

rr_ExpenseExampleYear01

$ 154

Expense Example, with Redemption, 5 Years

rr_ExpenseExampleYear05

563

Expense Example, No Redemption, 1 Year

rr_ExpenseExampleNoRedemptionYear01

104

Expense Example, No Redemption, 5 Years

rr_ExpenseExampleNoRedemptionYear05

563

1 Year

rr_AverageAnnualReturnYear01

4.64%

10 Years

rr_AverageAnnualReturnYear10

3.17%

Prospectus [Line Items]

rr_ProspectusLineItems

5 Years

rr_AverageAnnualReturnYear05

2.57%

Trading Symbol

dei_TradingSymbol

THIQX

Maximum Deferred Sales Charge (as a percentage)

rr_MaximumDeferredSalesChargeOverOther

0.65%

^[25],[26]

Distribution and Service (12b-1) Fees

rr_DistributionAndService12b1FeesOverAssets

0.65%

Expenses (as a percentage of Assets)

rr_ExpensesOverAssets

1.17%

Net Expenses (as a percentage of Assets)

rr_NetExpensesOverAssets

1.17%

Expense Example, with Redemption, 3 Years

rr_ExpenseExampleYear03

372

Expense Example, with Redemption, 10 Years

rr_ExpenseExampleYear10

1,420

Expense Example, No Redemption, 3 Years

rr_ExpenseExampleNoRedemptionYear03

372

Expense Example, No Redemption, 10 Years

rr_ExpenseExampleNoRedemptionYear10

$ 1,420

Prospectus [Line Items]

rr_ProspectusLineItems

Maximum Sales Charge Imposed on Purchases (as a percentage of Offering Price)

rr_MaximumSalesChargeImposedOnPurchasesOverOfferingPrice

none

Management Fees (as a percentage of Assets)

rr_ManagementFeesOverAssets

0.33%

Other Expenses (as a percentage of Assets):

rr_OtherExpensesOverAssets

0.20%

Fee Waiver or Reimbursement

rr_FeeWaiverOrReimbursementOverAssets

(0.04%)

^[24]

Expense Example, with Redemption, 1 Year

rr_ExpenseExampleYear01

$ 50

Expense Example, with Redemption, 5 Years

rr_ExpenseExampleYear05

292

1 Year

rr_AverageAnnualReturnYear01

5.75%

10 Years

rr_AverageAnnualReturnYear10

3.77%

Prospectus [Line Items]

rr_ProspectusLineItems

5 Years

rr_AverageAnnualReturnYear05

2.57%

Risk/Return [Heading]

rr_RiskReturnHeading

Fund Summary

Objective, Primary [Text Block]

rr_ObjectivePrimaryTextBlock

The Fund seeks long-term capital appreciation by investing in equity and debt securities of all types.

Expense [Heading]

rr_ExpenseHeading

Fees and Expenses of the Fund

Shareholder Fees Caption [Text]

rr_ShareholderFeesCaption

Shareholder Fees

Fee Waiver or Reimbursement over Assets, Date of Termination

rr_FeeWaiverOrReimbursementOverAssetsDateOfTermination

September 30, 2021

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 24.94% of the average value of its portfolio.

Expense Example [Heading]

rr_ExpenseExampleHeading

Example

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 Narrative [Text Block]

rr_StrategyNarrativeTextBlock

The Fund expects to invest primarily in domestic equity securities (primarily common stocks) selected on a value basis. However, the Fund may own a variety of securities, including foreign equity securities and foreign and domestic debt obligations which, in the opinion of the Fund’s investment advisor, Thornburg Investment Management, Inc. (“Thornburg”), offer prospects for meeting the Fund’s investment goals.

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 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 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 (which could include developing countries).

Debt obligations may be considered for investment if Thornburg believes them to be more attractive than equity alternatives, or to manage risk. 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.

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.

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.

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. These risks may be more pronounced for investments in developing countries.

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 debt 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 (including particularly “junk” or “high yield” bonds) 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.

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. Decreases in market interest rates may result in prepayments of debt obligations the Fund acquires, requiring the Fund to reinvest at lower interest rates.

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 51.

Risk Not Insured Depository Institution [Text]

rr_RiskNotInsuredDepositoryInstitution

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.

Performance Narrative [Text Block]

rr_PerformanceNarrativeTextBlock

The following information provides some indication of the risks of investing in 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 S&P 500 Total Return 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, 2019. Updated performance information may be obtained on the Thornburg website at www.thornburg.com or by calling 1-800-847-0200.

Performance Additional Market Index [Text]

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The average annual total return figures compare Class A, Class C and Class I share performance to the S&P 500 Total Return Index, a broad measure of market performance.

Performance Availability Website Address [Text]

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www.thornburg.com

Bar Chart [Heading]

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Annual Total Returns – Class A Shares

Bar Chart Closing [Text Block]

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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 Uses Highest Federal Rate

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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 One Class of after Tax Shown [Text]

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The after-tax returns shown relate only to Class A shares, and after-tax returns for other share classes will vary.

Risk/Return [Heading]

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Fund Summary

Objective, Primary [Text Block]

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The Fund seeks long-term capital appreciation by investing in equity and debt securities of all types.

Expense [Heading]

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Fees and Expenses of the Fund

Shareholder Fees Caption [Text]

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Shareholder Fees

Fee Waiver or Reimbursement over Assets, Date of Termination

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September 30, 2021

Portfolio Turnover [Text Block]

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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 24.94% of the average value of its portfolio.

Expense Example [Heading]

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Example

Strategy [Heading]

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Principal Investment Strategies

Risk [Heading]

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Principal Investment Risks

Risk Lose Money [Text]

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Accordingly, the loss of money is a risk of investing in the Fund.

Bar Chart and Performance Table [Heading]

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Past Performance of the Fund

Performance Information Illustrates Variability of Returns [Text]

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The following information provides some indication of the risks of investing in Value Fund by showing how the Fund’s investment results vary from year to year.

Performance Availability Phone [Text]

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1-800-847-0200

Performance Past Does Not Indicate Future [Text]

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Past performance (before and after taxes) is not necessarily an indication of how the Fund will perform in the future.

Performance Table Heading

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Average Annual Total Returns

Performance Table Not Relevant to Tax Deferred

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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]

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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.

Prospectus [Line Items]

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Maximum Sales Charge Imposed on Purchases (as a percentage of Offering Price)

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4.50%

Management Fees (as a percentage of Assets)

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0.85%

Other Expenses (as a percentage of Assets):

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0.23%

Fee Waiver or Reimbursement

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(0.15%)

^[29]

Expense Example, with Redemption, 1 Year

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$ 565

Expense Example, with Redemption, 5 Years

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1,127

Annual Return 2010

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9.15%

Annual Return 2012

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10.65%

Annual Return 2014

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11.50%

Annual Return 2016

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6.60%

Annual Return 2018

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(9.69%)

Highest Quarterly Return, Label

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Highest Quarterly Results

Highest Quarterly Return

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30.04%

Lowest Quarterly Return, Date

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Sep. 30, 2011

1 Year

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23.08%

10 Years

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9.41%

Prospectus [Line Items]

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5 Years

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8.45%

1 Year

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13.66%

10 Years

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7.69%

Prospectus [Line Items]

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5 Years

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11.70%

Trading Symbol

dei_TradingSymbol

TVCFX

Maximum Deferred Sales Charge (as a percentage)

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1.00%

^[30]

Distribution and Service (12b-1) Fees

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1.00%

Expenses (as a percentage of Assets)

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2.19%

Net Expenses (as a percentage of Assets)

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2.04%

Expense Example, with Redemption, 3 Years

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666

Expense Example, with Redemption, 10 Years

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2,508

Expense Example, No Redemption, 3 Years

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666

Expense Example, No Redemption, 10 Years

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$ 2,508

5 Years

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8.76%

1 Year

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31.49%

10 Years

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13.56%

Prospectus [Line Items]

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Maximum Sales Charge Imposed on Purchases (as a percentage of Offering Price)

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none

Management Fees (as a percentage of Assets)

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0.85%

Other Expenses (as a percentage of Assets):

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0.22%

Fee Waiver or Reimbursement

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(0.23%)

^[29]

Expense Example, with Redemption, 1 Year

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$ 86

Expense Example, with Redemption, 5 Years

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560

1 Year

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29.32%

10 Years

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10.33%

Prospectus [Line Items]

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5 Years

rr_AverageAnnualReturnYear05

11.70%

Trading Symbol

dei_TradingSymbol

TVRFX

Maximum Deferred Sales Charge (as a percentage)

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none

Distribution and Service (12b-1) Fees

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0.50%

Expenses (as a percentage of Assets)

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1.79%

Net Expenses (as a percentage of Assets)

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1.20%

Expense Example, with Redemption, 3 Years

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486

Expense Example, with Redemption, 10 Years

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$ 2,039

Annual Return 2011

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(13.50%)

Annual Return 2013

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39.56%

Annual Return 2015

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3.45%

Annual Return 2017

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23.35%

Annual Return 2019

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28.86%

Highest Quarterly Return, Date

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Jun. 30, 2009

Lowest Quarterly Return, Label

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Lowest Quarterly Results

Lowest Quarterly Return

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(22.51%)

5 Years

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9.63%

1 Year

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28.67%

10 Years

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9.80%

Prospectus [Line Items]

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5 Years

rr_AverageAnnualReturnYear05

7.55%

1 Year

rr_AverageAnnualReturnYear01

31.49%

10 Years

rr_AverageAnnualReturnYear10

13.56%

Prospectus [Line Items]

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Maximum Sales Charge Imposed on Purchases (as a percentage of Offering Price)

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none

Management Fees (as a percentage of Assets)

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0.85%

Other Expenses (as a percentage of Assets):

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0.65%

Fee Waiver or Reimbursement

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(0.65%)

^[31]

Expense Example, with Redemption, 1 Year

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$ 112

Expense Example, with Redemption, 5 Years

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867

1 Year

rr_AverageAnnualReturnYear01

28.98%

10 Years

rr_AverageAnnualReturnYear10

10.03%

Prospectus [Line Items]

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5 Years

rr_AverageAnnualReturnYear05

11.70%

Trading Symbol

dei_TradingSymbol

TVRRX

Maximum Deferred Sales Charge (as a percentage)

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none

Distribution and Service (12b-1) Fees

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none

Expenses (as a percentage of Assets)

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1.43%

Net Expenses (as a percentage of Assets)

rr_NetExpensesOverAssets

0.84%

Expense Example, with Redemption, 3 Years

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374

Expense Example, with Redemption, 10 Years

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$ 1,644

5 Years

rr_AverageAnnualReturnYear05

10.02%

1 Year

rr_AverageAnnualReturnYear01

31.49%

10 Years

rr_AverageAnnualReturnYear10

13.56%

Prospectus [Line Items]

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Objective [Heading]

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Investment Goal

Expense [Heading]

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Fees and Expenses of the Fund

Shareholder Fees Caption [Text]

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Shareholder Fees

Fee Waiver or Reimbursement over Assets, Date of Termination

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September 30, 2021

Portfolio Turnover [Text Block]

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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 40.69% of the average value of its portfolio.

Expense Example [Heading]

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Example

Expense Example, No Redemption Narrative [Text Block]

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You would pay the following expenses if you did not redeem your Class C shares:

Strategy Narrative [Text Block]

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The Fund expects to invest primarily in domestic equity securities (primarily common stocks) selected for their growth potential. However, the Fund may own a variety of securities, including foreign 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 debt and equity securities.

Debt obligations, usually with associated equity features, occasionally will be considered for investment when Thornburg believes them to be more attractive than equity alternatives. 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.