Label	Element	Value
Risk/Return:	rr_RiskReturnAbstract
Registrant Name	dei_EntityRegistrantName	THORNBURG INVESTMENT TRUST
Prospectus Date	rr_ProspectusDate	Feb. 01, 2015
Thornburg Developing World Fund | A C I
Risk/Return:	rr_RiskReturnAbstract
Risk/Return [Heading]	rr_RiskReturnHeading	FUND SUMMARY Developing World Fund
Objective [Heading]	rr_ObjectiveHeading	Investment Goal
Objective, Primary [Text Block]	rr_ObjectivePrimaryTextBlock	The Fund’s primary investment goal is long-term capital appreciation.
Expense [Heading]	rr_ExpenseHeading	Fees and Expenses of the Fund
Expense Narrative [Text Block]	rr_ExpenseNarrativeTextBlock	This table describes the fees and expenses that you may pay if you buy and hold shares of the Fund. You may qualify for discounts from the sales charge applicable to Class A shares if you or other qualifying account holders invest, or agree to invest in the future, at least $50,000 in the Thornburg Funds. More information about these and other discounts is available from your financial professional and in “Opening Your Account - Buying Fund Shares” on page 82 of this Prospectus.
Shareholder Fees Caption [Text]	rr_ShareholderFeesCaption	Shareholder Fees (fees paid directly from your investment)
Operating Expenses Caption [Text]	rr_OperatingExpensesCaption	Annual Fund Operating Expenses (expenses that you pay each year as a percentage of the value of your investment)
Portfolio Turnover [Heading]	rr_PortfolioTurnoverHeading	Portfolio Turnover.
Portfolio Turnover [Text Block]	rr_PortfolioTurnoverTextBlock	The Fund pays transaction costs, such as commissions, when it buys and sells securities (or “turns over” its portfolio). A higher portfolio turnover rate may indicate higher transaction costs and may result in higher taxes when Fund shares are held in a taxable account. These costs, which are not reflected in Annual Fund Operating Expenses or in the Example, affect the Fund’s performance. During the most recent fiscal year, the Fund’s portfolio turnover rate was 61.46% of the average value of its portfolio.
Portfolio Turnover, Rate	rr_PortfolioTurnoverRate	61.46%
Expense Breakpoint Discounts [Text]	rr_ExpenseBreakpointDiscounts	You may qualify for discounts from the sales charge applicable to Class A shares if you or other qualifying account holders invest, or agree to invest in the future, at least $50,000 in the Thornburg Funds. More information about these and other discounts is available from your financial professional and in “Opening Your Account - Buying Fund Shares” on page 82 of this Prospectus.
Expense Breakpoint, Minimum Investment Required [Amount]	rr_ExpenseBreakpointMinimumInvestmentRequiredAmount	50,000
Expense Example [Heading]	rr_ExpenseExampleHeading	Example.
Expense Example Narrative [Text Block]	rr_ExpenseExampleNarrativeTextBlock	This Example is intended to help you compare the cost of investing in the Fund with the cost of investing in other mutual funds. The Example assumes that you invest $10,000 in the Fund for the time periods indicated and then redeem all of your shares at the end of those periods. The Example also assumes that your investment has a 5% return each year, dividends and distributions are reinvested, and that the Fund’s operating expenses remain the same. Although your actual costs may be higher or lower, based on these assumptions, your costs would be:
Expense Example, No Redemption, By Year, Caption [Text]	rr_ExpenseExampleNoRedemptionByYearCaption	You would pay the following expenses if you did not redeem your Class C shares:
Strategy [Heading]	rr_StrategyHeading	Principal Investment Strategies
Strategy Narrative [Text Block]	rr_StrategyNarrativeTextBlock	Under normal market conditions the Fund invests at least 80% of its assets in equity securities and debt obligations of developing country issuers. A developing country issuer is a company or sovereign entity that is domiciled or otherwise tied economically to one or more developing countries. The Fund expects that investments in the Fund’s portfolio normally will be weighted in favor of equity securities. The Fund’s investment in debt obligations may include, but is not limited to, those of sovereign and corporate issuers. The Fund may purchase debt obligations of any maturity and credit quality, including “high yield” or “junk” bonds. There is no minimum credit quality or rating of debt obligation the Fund may purchase. The Fund also may invest in debt obligations which have a combination of equity and debt characteristics (such as convertible bonds). The Fund may invest in issuers of any size of capitalization, including small companies. Currently, the Fund’s investment advisor, Thornburg Investment Management, Inc. (“Thornburg”) considers developing countries to include most Central and South American, African, Asian and Eastern European nations, including, but not limited to, Argentina, Austria, Brazil, Chile, China, Colombia, Czech Republic, Egypt, Hong Kong, Hungary, India, Indonesia, Israel, South Korea, Malaysia, Mexico, Morocco, Nigeria, Pakistan, Peru, Philippines, Poland, Qatar, Romania, the Russian Federation, Slovenia, South Africa, Taiwan, Thailand, Turkey, Ukraine, the United Arab Emirates and Vietnam. Thornburg identifies what it considers to be developing countries based upon its own analysis of measures of industrialization, economic growth, population growth and other factors, and may also consider classifications by the World Bank, the International Finance Corporation, the United Nations and independent financial services firms that maintain indices of developing countries. Thornburg considers a variety of factors to determine whether an investment is tied economically to one or more developing countries, including (i) whether or not a significant portion of the issuer’s revenues or assets are derived from or are located in developing countries, (ii) the primary trading market of the issuer’s securities, (iii) the locations of its offices or other operations, (iv) the source of any governmental guarantees or other supports, (v) identification of the issuer’s securities within an index or other listing indicating its location in a particular developing country or region, and (vi) whether the investment is otherwise exposed to the economic fortunes and risks of developing countries. The Fund’s policy of investing at least 80% of its assets in developing country issuers may be changed by the Fund’s Trustees without a shareholder vote upon 60 days’ notice to shareholders. Among the specific factors considered in identifying securities for inclusion in the Fund are domestic and international economic developments, outlooks for securities markets, interest rates and inflation, the supply and demand for debt and equity securities, and analysis of specific issuers. With respect to equity securities, the Fund typically makes investments in the following three types of issuers: Basic Value: Companies which, in Thornburg’s opinion, are financially sound with well established businesses selling at low valuations relative to the companies’ net assets or potential earning power. Consistent Earner: Companies which normally exhibit steady earnings growth, cash flow characteristics and/or dividend growth. These companies may have above average profitability measures and normally sell at above average valuations. Emerging Franchise: Companies which, in Thornburg’s opinion, are in the process of establishing a leading position in a product, service or market with the potential to grow at an above average rate.
Risk [Heading]	rr_RiskHeading	Principal Investment Risks
Risk Narrative [Text Block]	rr_RiskNarrativeTextBlock	An investment in the Fund is not a deposit in any bank and is not insured or guaranteed by the Federal Deposit Insurance Corporation or any other governmental agency. Accordingly, the loss of money is a risk of investing in the Fund. The value of the Fund’s shares varies from day to day and over time, and when you sell your shares they may be worth less than what you paid for them. The following is a summary of the principal risks of investing in the Fund. Management Risk – The Fund is an actively managed portfolio, and the value of the Fund may be reduced if Thornburg pursues unsuccessful investments or fails to correctly identify risks affecting the broad economy or specific issuers in which the Fund invests. Market and Economic Risk – The value of the Fund’s investments may decline and its share value may be reduced due to changes in general economic and market conditions. The value of a security may change in response to developments affecting entire economies, markets or industries, including changes in interest rates, political and legal developments, and general market volatility. These risks may be more pronounced for the Fund’s investments in developing countries. Risks Affecting Specific Issuers – The value of an equity security or debt obligation may decline in response to developments affecting the specific issuer of the security or obligation, even if the overall industry or economy is unaffected. These developments may include a variety of factors, including but not limited to management issues or other corporate disruption, a decline in revenues or profitability, an increase in costs, or an adverse effect on the issuer’s competitive position. Foreign Investment Risk – Investments in securities of foreign issuers may involve risks including adverse fluctuations in currency exchange rates, political instability, confiscations, taxes or restrictions on currency exchange, difficulty in selling foreign investments, and reduced legal protections. Developing Country Risk – The risks which may affect investments in foreign issuers (see “Foreign Investment Risk,” above) may be more pronounced for investments in developing countries because the economies of those countries are usually less diversified, communications, transportation and economic infrastructures are less developed, and developing countries ordinarily have less established legal, political, business and social frameworks. At times the prices of equity securities or debt obligations of a developing country issuer may be extremely volatile. An issuer domiciled in a developed country may be similarly affected by these developing country risks to the extent that the issuer conducts a significant percentage of its business in developing countries. Small and Mid-Cap Company Risk – Investments in small-capitalization companies and mid-capitalization companies may involve additional risks, which may be relatively higher with smaller companies. These additional risks may result from limited product lines, more limited access to markets and financial resources, greater vulnerability to competition and changes in markets, lack of management depth, increased volatility in share price, and possible difficulties in valuing or selling these investments. Credit Risk – If debt obligations held by the Fund are downgraded by ratings agencies or go into default, or if management action, legislation or other government action reduces the ability of issuers to pay principal and interest when due, the value of those obligations may decline and the Fund’s share value and any dividends paid by the Fund may be reduced. Some foreign government debt obligations may be subject to default, repudiation or renegotiation, delays in payment, or could be downgraded by ratings agencies. Additionally, 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 the investments promptly, or may only be able to sell investments at less than desired prices. This risk may be more pronounced for the Fund’s investments in developing countries. Additional information about Fund investments, investment strategies and risks of investing in the Fund appears below beginning on page 74.
Risk Lose Money [Text]	rr_RiskLoseMoney	Accordingly, the loss of money is a risk of investing in the Fund.
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.
Bar Chart and Performance Table [Heading]	rr_BarChartAndPerformanceTableHeading	Past Performance of the Fund
Performance Narrative [Text Block]	rr_PerformanceNarrativeTextBlock	The following information provides some indication of the risks of investing in Developing World Fund by showing how the Fund’s investment results vary from year to year. The bar chart shows how the annual total returns for Class A shares have been different in each full year shown. The average annual total return figures compare Class A, Class C and Class I share performance to the Morgan Stanley Capital International (MSCI) Emerging Markets Index, which represents a broad measure of equity market performance of emerging markets. Past performance (before and after taxes) is not necessarily an indication of how the Fund will perform in the future. The performance information shown below is as of the calendar year ended December 31, 2014. Updated performance information may be obtained on the Thornburg website at www.thornburg.com or by calling 1-800-847-0200.
Performance Information Illustrates Variability of Returns [Text]	rr_PerformanceInformationIllustratesVariabilityOfReturns	The following information provides some indication of the risks of investing in Developing World Fund by showing how the Fund’s investment results vary from year to year.
Performance Additional Market Index [Text]	rr_PerformanceAdditionalMarketIndex	The average annual total return figures compare Class A, Class C and Class I share performance to the Morgan Stanley Capital International (MSCI) Emerging Markets Index, which represents a broad measure of equity market performance of emerging markets.
Performance Availability Phone [Text]	rr_PerformanceAvailabilityPhone	1-800-847-0200
Performance Availability Website Address [Text]	rr_PerformanceAvailabilityWebSiteAddress	www.thornburg.com
Performance Past Does Not Indicate Future [Text]	rr_PerformancePastDoesNotIndicateFuture	Past performance (before and after taxes) is not necessarily an indication of how the Fund will perform in the future.
Bar Chart [Heading]	rr_BarChartHeading	Annual Total Returns – Class A Shares
Bar Chart Does Not Reflect Sales Loads [Text]	rr_BarChartDoesNotReflectSalesLoads	The sales charge for Class A shares is not reflected in the returns shown on the bar chart, and the returns would be less if the charge was taken into account.
Bar Chart Closing [Text Block]	rr_BarChartClosingTextBlock	Highest quarterly results for time period shown: 18.17% (quarter ended 9-30-10). Lowest quarterly results for time period shown: -23.17% (quarter ended 9-30-11). The sales charge for Class A shares is not reflected in the returns shown on the bar chart, and the returns would be less if the charge was taken into account.
Performance Table Heading	rr_PerformanceTableHeading	Average Annual Total Returns (periods ended 12-31-14)
Performance Table Uses Highest Federal Rate	rr_PerformanceTableUsesHighestFederalRate	After-tax returns are calculated using the historical highest individual federal marginal income tax rates, and do not reflect state or local income taxes.
Performance Table Not Relevant to Tax Deferred	rr_PerformanceTableNotRelevantToTaxDeferred	Actual after-tax returns depend on an investor’s own tax situation and may differ from the returns shown, and after-tax returns shown are not relevant to investors who hold their Fund shares through tax-deferred arrangements, such as 401(k) plans or individual retirement accounts.
Performance Table One Class of after Tax Shown [Text]	rr_PerformanceTableOneClassOfAfterTaxShown	The after-tax returns shown relate only to Class A shares, and after-tax returns will vary for Class C and Class I shares because the returns of the classes are different.
Performance Table Narrative	rr_PerformanceTableNarrativeTextBlock	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 will vary for Class C and Class I shares because the returns of the classes are different.
Thornburg Developing World Fund | A C I | Class A
Risk/Return:	rr_RiskReturnAbstract
Maximum Sales Charge (Load) Imposed on Purchases (as a percentage of offering price)	rr_MaximumSalesChargeImposedOnPurchasesOverOfferingPrice	4.50%
Maximum Deferred Sales Charge (Load) (as a percentage of redemption proceeds or original purchase price, whichever is lower)	rr_MaximumDeferredSalesChargeOverOther	none	[1]
Management Fees	rr_ManagementFeesOverAssets	0.82%
Distribution and Service (12b-1) Fees	rr_DistributionAndService12b1FeesOverAssets	0.25%
Other Expenses	rr_OtherExpensesOverAssets	0.38%
Total Annual Fund Operating Expenses	rr_ExpensesOverAssets	1.45%
Expenses Deferred Charges [Text Block]	rr_ExpensesDeferredChargesTextBlock	A 1.00% contingent deferred sales charge (CDSC) is imposed on redemptions of any part or all of a purchase of $1 million or more within 12 months of purchase.
1 Year	rr_ExpenseExampleYear01	591
3 Years	rr_ExpenseExampleYear03	888
5 Years	rr_ExpenseExampleYear05	1,207
10 Years	rr_ExpenseExampleYear10	2,107
2010	rr_AnnualReturn2010	30.73%
2011	rr_AnnualReturn2011	(15.63%)
2012	rr_AnnualReturn2012	22.70%
2013	rr_AnnualReturn2013	15.61%
2014	rr_AnnualReturn2014	(3.04%)
Highest Quarterly Return, Label	rr_HighestQuarterlyReturnLabel	Highest quarterly results
Highest Quarterly Return, Date	rr_BarChartHighestQuarterlyReturnDate	Sep. 30, 2010
Highest Quarterly Return	rr_BarChartHighestQuarterlyReturn	18.17%
Lowest Quarterly Return, Label	rr_LowestQuarterlyReturnLabel	Lowest quarterly results
Lowest Quarterly Return, Date	rr_BarChartLowestQuarterlyReturnDate	Sep. 30, 2011
Lowest Quarterly Return	rr_BarChartLowestQuarterlyReturn	(23.17%)
1 Year	rr_AverageAnnualReturnYear01	(7.39%)
5 Years	rr_AverageAnnualReturnYear05	7.69%
Since Inception	rr_AverageAnnualReturnSinceInception	7.74%
Inception Date	rr_AverageAnnualReturnInceptionDate	Dec. 16, 2009
Thornburg Developing World Fund | A C I | Class C
Risk/Return:	rr_RiskReturnAbstract
Maximum Sales Charge (Load) Imposed on Purchases (as a percentage of offering price)	rr_MaximumSalesChargeImposedOnPurchasesOverOfferingPrice	none
Maximum Deferred Sales Charge (Load) (as a percentage of redemption proceeds or original purchase price, whichever is lower)	rr_MaximumDeferredSalesChargeOverOther	1.00%	[2]
Management Fees	rr_ManagementFeesOverAssets	0.82%
Distribution and Service (12b-1) Fees	rr_DistributionAndService12b1FeesOverAssets	1.00%
Other Expenses	rr_OtherExpensesOverAssets	0.41%
Total Annual Fund Operating Expenses	rr_ExpensesOverAssets	2.23%
Expenses Deferred Charges [Text Block]	rr_ExpensesDeferredChargesTextBlock	Imposed only on redemptions of Class C shares within 12 months of purchase.
1 Year	rr_ExpenseExampleYear01	326
3 Years	rr_ExpenseExampleYear03	697
5 Years	rr_ExpenseExampleYear05	1,195
10 Years	rr_ExpenseExampleYear10	2,565
1 Year	rr_ExpenseExampleNoRedemptionYear01	226
3 Years	rr_ExpenseExampleNoRedemptionYear03	697
5 Years	rr_ExpenseExampleNoRedemptionYear05	1,195
10 Years	rr_ExpenseExampleNoRedemptionYear10	2,565
1 Year	rr_AverageAnnualReturnYear01	(4.80%)
5 Years	rr_AverageAnnualReturnYear05	7.93%
Since Inception	rr_AverageAnnualReturnSinceInception	7.97%
Inception Date	rr_AverageAnnualReturnInceptionDate	Dec. 16, 2009
Thornburg Developing World Fund | A C I | Class I
Risk/Return:	rr_RiskReturnAbstract
Maximum Sales Charge (Load) Imposed on Purchases (as a percentage of offering price)	rr_MaximumSalesChargeImposedOnPurchasesOverOfferingPrice	none
Maximum Deferred Sales Charge (Load) (as a percentage of redemption proceeds or original purchase price, whichever is lower)	rr_MaximumDeferredSalesChargeOverOther	none
Management Fees	rr_ManagementFeesOverAssets	0.82%
Distribution and Service (12b-1) Fees	rr_DistributionAndService12b1FeesOverAssets	none
Other Expenses	rr_OtherExpensesOverAssets	0.27%
Total Annual Fund Operating Expenses	rr_ExpensesOverAssets	1.09%
1 Year	rr_ExpenseExampleYear01	111
3 Years	rr_ExpenseExampleYear03	347
5 Years	rr_ExpenseExampleYear05	601
10 Years	rr_ExpenseExampleYear10	1,329
1 Year	rr_AverageAnnualReturnYear01	(2.69%)
5 Years	rr_AverageAnnualReturnYear05	9.28%
Since Inception	rr_AverageAnnualReturnSinceInception	9.31%
Inception Date	rr_AverageAnnualReturnInceptionDate	Dec. 16, 2009
Thornburg Developing World Fund | A C I | Return After Taxes on Distributions | Class A
Risk/Return:	rr_RiskReturnAbstract
1 Year	rr_AverageAnnualReturnYear01	(7.40%)
5 Years	rr_AverageAnnualReturnYear05	7.68%
Since Inception	rr_AverageAnnualReturnSinceInception	7.72%
Inception Date	rr_AverageAnnualReturnInceptionDate	Dec. 16, 2009
Thornburg Developing World Fund | A C I | Return After Taxes on Distributions and Sale of Fund Shares | Class A
Risk/Return:	rr_RiskReturnAbstract
1 Year	rr_AverageAnnualReturnYear01	(4.19%)
5 Years	rr_AverageAnnualReturnYear05	6.05%
Since Inception	rr_AverageAnnualReturnSinceInception	6.09%
Inception Date	rr_AverageAnnualReturnInceptionDate	Dec. 16, 2009
Thornburg Developing World Fund | A C I | MSCI Emerging Markets Index (reflects no deduction for fees, expenses, or taxes) | Class A
Risk/Return:	rr_RiskReturnAbstract
1 Year	rr_AverageAnnualReturnYear01	(2.19%)
5 Years	rr_AverageAnnualReturnYear05	1.78%
Since Inception	rr_AverageAnnualReturnSinceInception	2.11%
Inception Date	rr_AverageAnnualReturnInceptionDate	Dec. 16, 2009
Thornburg Developing World Fund | A C I | MSCI Emerging Markets Index (reflects no deduction for fees, expenses, or taxes) | Class C
Risk/Return:	rr_RiskReturnAbstract
1 Year	rr_AverageAnnualReturnYear01	(2.19%)
5 Years	rr_AverageAnnualReturnYear05	1.78%
Since Inception	rr_AverageAnnualReturnSinceInception	2.11%
Inception Date	rr_AverageAnnualReturnInceptionDate	Dec. 16, 2009
Thornburg Developing World Fund | A C I | MSCI Emerging Markets Index (reflects no deduction for fees, expenses, or taxes) | Class I
Risk/Return:	rr_RiskReturnAbstract
1 Year	rr_AverageAnnualReturnYear01	(2.19%)
5 Years	rr_AverageAnnualReturnYear05	1.78%
Since Inception	rr_AverageAnnualReturnSinceInception	2.11%
Inception Date	rr_AverageAnnualReturnInceptionDate	Dec. 16, 2009

[1] A 1.00% contingent deferred sales charge (CDSC) is imposed on redemptions of any part or all of a purchase of $1 million or more within 12 months of purchase.

[2] Imposed only on redemptions of Class C shares within 12 months of purchase.