Label

Element

Value

Risk/Return:

rr_RiskReturnAbstract

Registrant Name

dei_EntityRegistrantName

THORNBURG INVESTMENT TRUST

Prospectus Date

rr_ProspectusDate

Feb. 01, 2015

Thornburg Value Fund | R3 R4 R5

Risk/Return:

rr_RiskReturnAbstract

Risk/Return [Heading]

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FUND SUMMARY

Value Fund

Objective [Heading]

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Investment Goal

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.

Objective, Secondary [Text Block]

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

Expense [Heading]

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Fees and Expenses of the Fund

Expense Narrative [Text Block]

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

Shareholder Fees Caption [Text]

rr_ShareholderFeesCaption

Shareholder Fees
(fees paid directly from your investment)

Operating Expenses Caption [Text]

rr_OperatingExpensesCaption

Annual Fund Operating Expenses
(expenses that you pay each year as a percentage of the value of your investment)

Fee Waiver or Reimbursement over Assets, Date of Termination

rr_FeeWaiverOrReimbursementOverAssetsDateOfTermination

February 1, 2016

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 72.43% of the average value of its portfolio.

Portfolio Turnover, Rate

rr_PortfolioTurnoverRate

72.43%

Expense Example [Heading]

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Example.

Expense Example Narrative [Text Block]

rr_ExpenseExampleNarrativeTextBlock

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

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

Strategy [Heading]

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Principal Investment Strategies

Strategy Narrative [Text Block]

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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, partnership interests 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 classified 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	■	undervalued assets
■	price/earnings ratio	■	earnings growth potential
■	price/book value ratio	■	industry growth characteristics
■	price/cash flow ratio	■	industry leadership
■	debt/capital ratio	■	franchise value
■	dividend characteristics	■	potential for favorable developments
■	security and consistency of revenues	■	EBIT (earnings before interest and taxes)/interest expense ratio
■	EV (enterprise value)/ EBITDA (earnings before interest, taxes, depreciation and amortization) ratio

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

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. Under normal conditions, the proportion of the Fund invested in this category will be lower than the other categories.

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 [Heading]

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Principal Investment Risks

Risk Narrative [Text Block]

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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 the 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 38.

Risk Lose Money [Text]

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

Risk Not Insured Depository Institution [Text]

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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]

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Past Performance of the Fund

Performance Narrative [Text Block]

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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. The bar chart shows how the annual total returns for Class R3 shares have been different in each full year shown. The average annual total return figures compare Class R3, Class R4 and Class R5 share performance to the Standard & Poor’s 500 Composite 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 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]

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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 Additional Market Index [Text]

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The average annual total return figures compare Class R3, Class R4 and Class R5 share performance to the Standard & Poor’s 500 Composite Index, a broad measure of market performance.

Performance Availability Phone [Text]

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1-800-847-0200

Performance Availability Website Address [Text]

rr_PerformanceAvailabilityWebSiteAddress

www.thornburg.com

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.

Bar Chart [Heading]

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Annual Total Returns – Class R3 Shares

Bar Chart Closing [Text Block]

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Highest quarterly results for time period shown: 30.07%
(quarter ended 6-30-09).

Lowest quarterly results for time period shown: -22.51%
(quarter ended 9-30-11).

Performance Table Heading

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Average Annual Total Returns (periods ended 12-31-14)

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 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 Narrative

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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

Thornburg Value Fund | R3 R4 R5 | Class R3

Risk/Return:

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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

0.76%

Distribution and Service (12b-1) Fees

rr_DistributionAndService12b1FeesOverAssets

0.50%

Other Expenses

rr_OtherExpensesOverAssets

0.51%

Total Annual Fund Operating Expenses

rr_ExpensesOverAssets

1.77%

Fee Waiver/Expense Reimbursement

rr_FeeWaiverOrReimbursementOverAssets

(0.42%)

^[1]

Total Annual Fund Operating Expenses After Fee Waiver/Expense Reimbursement

rr_NetExpensesOverAssets

1.35%

1 Year

rr_ExpenseExampleYear01

137

3 Years

rr_ExpenseExampleYear03

516

5 Years

rr_ExpenseExampleYear05

920

10 Years

rr_ExpenseExampleYear10

2,049

2005

rr_AnnualReturn2005

9.52%

2006

rr_AnnualReturn2006

21.86%

2007

rr_AnnualReturn2007

6.08%

2008

rr_AnnualReturn2008

(41.57%)

2009

rr_AnnualReturn2009

45.12%

2010

rr_AnnualReturn2010

9.13%

2011

rr_AnnualReturn2011

(13.50%)

2012

rr_AnnualReturn2012

10.66%

2013

rr_AnnualReturn2013

39.56%

2014

rr_AnnualReturn2014

11.51%

Highest Quarterly Return, Label

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Highest quarterly results

Highest Quarterly Return, Date

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Jun. 30, 2009

Highest Quarterly Return

rr_BarChartHighestQuarterlyReturn

30.07%

Lowest Quarterly Return, Label

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Lowest quarterly results

Lowest Quarterly Return, Date

rr_BarChartLowestQuarterlyReturnDate

Sep. 30, 2011

Lowest Quarterly Return

rr_BarChartLowestQuarterlyReturn

(22.51%)

1 Year

rr_AverageAnnualReturnYear01

11.51%

5 Years

rr_AverageAnnualReturnYear05

10.21%

10 Years

rr_AverageAnnualReturnYear10

6.91%

Thornburg Value Fund | R3 R4 R5 | Class R4

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

0.76%

Distribution and Service (12b-1) Fees

rr_DistributionAndService12b1FeesOverAssets

0.25%

Other Expenses

rr_OtherExpensesOverAssets

0.68%

Total Annual Fund Operating Expenses

rr_ExpensesOverAssets

1.69%

Fee Waiver/Expense Reimbursement

rr_FeeWaiverOrReimbursementOverAssets

(0.44%)

^[1]

Total Annual Fund Operating Expenses After Fee Waiver/Expense Reimbursement

rr_NetExpensesOverAssets

1.25%

1 Year

rr_ExpenseExampleYear01

127

3 Years

rr_ExpenseExampleYear03

490

5 Years

rr_ExpenseExampleYear05

876

10 Years

rr_ExpenseExampleYear10

1,961

1 Year

rr_AverageAnnualReturnYear01

11.62%

5 Years

rr_AverageAnnualReturnYear05

10.32%

Since Inception

rr_AverageAnnualReturnSinceInception

4.45%

Inception Date

rr_AverageAnnualReturnInceptionDate

Feb. 01, 2007

Thornburg Value Fund | R3 R4 R5 | Class R5

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

0.76%

Distribution and Service (12b-1) Fees

rr_DistributionAndService12b1FeesOverAssets

none

Other Expenses

rr_OtherExpensesOverAssets

0.66%

Total Annual Fund Operating Expenses

rr_ExpensesOverAssets

1.42%

Fee Waiver/Expense Reimbursement

rr_FeeWaiverOrReimbursementOverAssets

(0.43%)

^[1]

Total Annual Fund Operating Expenses After Fee Waiver/Expense Reimbursement

rr_NetExpensesOverAssets

0.99%

1 Year

rr_ExpenseExampleYear01

101

3 Years

rr_ExpenseExampleYear03

407

5 Years

rr_ExpenseExampleYear05

735

10 Years

rr_ExpenseExampleYear10

1,665

1 Year

rr_AverageAnnualReturnYear01

11.91%

5 Years

rr_AverageAnnualReturnYear05

10.60%

Since Inception

rr_AverageAnnualReturnSinceInception

7.58%

Inception Date

rr_AverageAnnualReturnInceptionDate

Feb. 01, 2005

Thornburg Value Fund | R3 R4 R5 | Return After Taxes on Distributions | Class R3

Risk/Return:

rr_RiskReturnAbstract

1 Year

rr_AverageAnnualReturnYear01

11.28%

5 Years

rr_AverageAnnualReturnYear05

10.14%

10 Years

rr_AverageAnnualReturnYear10

6.47%

Thornburg Value Fund | R3 R4 R5 | Return After Taxes on Distributions and Sale of Fund Shares | Class R3

Risk/Return:

rr_RiskReturnAbstract

1 Year

rr_AverageAnnualReturnYear01

6.51%

5 Years

rr_AverageAnnualReturnYear05

8.07%

10 Years

rr_AverageAnnualReturnYear10

5.50%

Thornburg Value Fund | R3 R4 R5 | S&P 500 Index (reflects no deduction for fees, expenses, or taxes) | Class R3

Risk/Return:

rr_RiskReturnAbstract

1 Year

rr_AverageAnnualReturnYear01

13.69%

5 Years

rr_AverageAnnualReturnYear05

15.45%

10 Years

rr_AverageAnnualReturnYear10

7.67%

Thornburg Value Fund | R3 R4 R5 | S&P 500 Index (reflects no deduction for fees, expenses, or taxes) | Class R4

Risk/Return:

rr_RiskReturnAbstract

1 Year

rr_AverageAnnualReturnYear01

13.69%

5 Years

rr_AverageAnnualReturnYear05

15.45%

Since Inception

rr_AverageAnnualReturnSinceInception

6.92%

Inception Date

rr_AverageAnnualReturnInceptionDate

Feb. 01, 2007

Thornburg Value Fund | R3 R4 R5 | S&P 500 Index (reflects no deduction for fees, expenses, or taxes) | Class R5

Risk/Return:

rr_RiskReturnAbstract

1 Year

rr_AverageAnnualReturnYear01

13.69%

5 Years

rr_AverageAnnualReturnYear05

15.45%

Since Inception

rr_AverageAnnualReturnSinceInception

8.01%

Inception Date

rr_AverageAnnualReturnInceptionDate

Feb. 01, 2005

[1] Thornburg Investment Management, Inc. ("Thornburg") and/or Thornburg Securities Corporation ("TSC") have contractually agreed to waive fees and reimburse expenses incurred by the Fund so that actual Class R3, Class R4 and Class R5 expenses do not exceed 1.35%, 1.25%, and 0.99%, respectively. The agreement to waive fees and reimburse expenses may be terminated by the Fund at any time, but may not be terminated by Thornburg or TSC before February 1, 2016, unless Thornburg or TSC ceases to be the investment advisor or distributor of the Fund prior to that date. Thornburg and TSC retain the ability to be repaid by the Fund for fee waivers and expense reimbursements during a fiscal year if Fund expenses fall below the relevant percentage threshold before the end of that fiscal year.