Fees and Expenses - Retail [Member]
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Aug. 20, 2026
USD ($)
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| Thornburg Investment Income Builder Fund |
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| Prospectus [Line Items] |
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| Expense Heading [Optional Text] |
Fees and Expenses of the Fund
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| Expense Narrative [Text Block] |
This table describes the fees and expenses that you may pay if you buy and hold shares of the Fund. You may pay other fees, such as brokerage commissions and other fees to financial intermediaries, which are not reflected in the tables and examples below. You may qualify for discounts from the sales charges applicable to Class A shares if you or other qualifying account holders invest, or agree to invest in the future, at least $50,000 in the Thornburg Funds. More information about this and other discounts and sales charge waivers is available from your financial intermediary, in the Prospectus under the captions “Class A Sales Charge Waivers,” beginning on page 154, and “Appendix A – Sales Charge Waivers Offered by Financial Intermediaries,” beginning on page 208, and in the Statement of Additional Information under the caption “Additional Information Respecting Purchase and Redemption of Shares,” beginning on page 94.
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| Expense Breakpoint Discounts [Text] |
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.
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| Expense Breakpoint, Minimum Investment Required [Amount] |
$ 50,000
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| Expenses Not Correlated to Ratio Due to Acquired Fund Fees [Text] |
The Total Annual Fund Operating Expenses and Total Annual Fund Operating Expenses After Fee Waiver/Expense Reimbursement do not match the Ratios to Average Net Assets shown in the Financial Highlights section of the Prospectus, which reflect the operating expenses of the Fund and do not include acquired fund fees and expenses (‘AFFE’). AFFE are expenses incurred indirectly by other investment companies in which the Fund holds shares, are not direct costs paid by Fund shareholders, and are not used to calculate the Fund’s net asset value.
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| Shareholder Fees Caption [Optional Text] |
Shareholder Fees
(fees paid directly from your investment)
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| Shareholder Fees [Table] |
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Class A |
Class C |
Class I |
Class R6 |
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Maximum Sales Charge (Load) Imposed on Purchases
(as a percentage of offering price) |
4.50% |
none |
none |
none |
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Maximum Deferred Sales Charge (Load)
(as a percentage of redemption proceeds or original purchase price, whichever is lower) |
none(1) |
1.00%(2) |
none |
none |
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| Operating Expenses Caption [Optional Text] |
Annual Fund Operating Expenses
(expenses that you pay each year as a percentage of the value of your investment)
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| Annual Fund Operating Expenses [Table] |
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Class A |
Class C |
Class I |
Class R6 |
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Management Fees |
0.69% |
0.69% |
0.69% |
0.69% |
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Distribution and Service (12b-1) Fees |
0.25% |
1.00% |
none |
none |
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Other Expenses |
0.18% |
0.18% |
0.19% |
0.13% |
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Acquired Fund Fees and Expenses |
0.03% |
0.03% |
0.03% |
0.03% |
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Total Annual Fund Operating Expenses(3) |
1.15% |
1.90% |
0.91% |
0.85% |
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Fee Waiver/Expense Reimbursement(4) |
— |
— |
— |
(0.02)% |
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Total Annual Fund Operating Expenses After
Fee Waiver/Expense Reimbursement(3) |
1.15% |
1.90% |
0.91% |
0.83% |
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| Expense Footnotes [Text Block] |
| (1) |
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Up to a 1.00% contingent deferred sales charge (CDSC) is imposed on redemptions of any part or all of a purchase of $1 million or more within 12 months of purchase. |
| (2) |
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Imposed only on redemptions of Class C shares within 12 months of purchase. |
| (3) |
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The Total Annual Fund Operating Expenses and Total Annual Fund Operating Expenses After Fee Waiver/Expense Reimbursement do not match the Ratios to Average Net Assets shown in the Financial Highlights section of the Prospectus, which reflect the operating expenses of the Fund and do not include acquired fund fees and expenses (‘AFFE’). AFFE are expenses incurred indirectly by other investment companies in which the Fund holds shares, are not direct costs paid by Fund shareholders, and are not used to calculate the Fund’s net asset value. |
| (4) |
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Thornburg Investment Management, Inc. (“Thornburg”) has contractually agreed to waive fees and reimburse expenses incurred by the Fund so that actual Class R6 expenses (excluding taxes, interest expenses, acquired fund fees and expenses, brokerage commissions, borrowing costs, expenses relating to short sales, and unusual expenses such as contingency fees or litigation costs) do not exceed 0.80%. The agreement to waive fees and reimburse expenses may be terminated by the Fund’s Trustees at any time, but may not be terminated by Thornburg before February 1, 2027, unless Thornburg ceases to be the investment advisor of the Fund prior to that date. Thornburg may recoup amounts waived or reimbursed during the Fund’s fiscal year if actual expenses fall below the expense cap during that same fiscal year. |
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| Expense Example [Heading] |
Example.
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| Expense Example Narrative [Text Block] |
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:
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| Expense Example, With Redemption [Table] |
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1 Year |
3 Years |
5 Years |
10 Years |
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Class A Shares |
$562 |
$799 |
$1,054 |
$1,785 |
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Class C Shares |
$293 |
$597 |
$1,026 |
$2,222 |
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Class I Shares |
$93 |
$290 |
$504 |
$1,120 |
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Class R6 Shares |
$85 |
$269 |
$469 |
$1,047 |
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| Expense Example, No Redemption, By Year, Caption [Text] |
You would pay the following expenses if you did not redeem your Class C shares:
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| Expense Example, No Redemption [Table] |
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1 Year |
3 Years |
5 Years |
10 Years |
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Class C Shares |
$193 |
$597 |
$1,026 |
$2,222 |
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| Portfolio Turnover [Heading] |
Portfolio Turnover.
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| Portfolio Turnover [Text Block] |
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 27.78% of the average value of its portfolio.
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| Portfolio Turnover, Rate |
27.78%
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| Thornburg Summit Fund |
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| Prospectus [Line Items] |
|
| Expense Heading [Optional Text] |
Fees and Expenses of the Fund
|
| Expense Narrative [Text Block] |
This table describes the fees and expenses that you may pay if you buy and hold shares of the Fund. You may pay other fees, such as brokerage commissions and other fees to financial intermediaries, which are not reflected in the tables and examples below. You may qualify for discounts from the sales charges applicable to Class A shares if you or other qualifying account holders invest, or agree to invest in the future, at least $50,000 in the Thornburg Funds. More information about this and other discounts and sales charge waivers is available from your financial intermediary, in the Prospectus under the captions “Class A Sales Charge Waivers,” beginning on page 154, and “Appendix A – Sales Charge Waivers Offered by Financial Intermediaries,” beginning on page 208, and in the Statement of Additional Information under the caption “Additional Information Respecting Purchase and Redemption of Shares,” beginning on page 94.
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| Expense Breakpoint Discounts [Text] |
You may qualify for discounts from the sales charges applicable to Class A shares if you or other qualifying account holders invest, or agree to invest in the future, at least $50,000 in the Thornburg Funds.
|
| Expense Breakpoint, Minimum Investment Required [Amount] |
$ 50,000
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| Expenses Not Correlated to Ratio Due to Acquired Fund Fees [Text] |
The Total Annual Fund Operating Expenses and Total Annual Fund Operating Expenses After Fee Waiver/Expense Reimbursement do not match the Ratios to Average Net Assets shown in the Financial Highlights section of the Prospectus, which reflect the operating expenses of the Fund and do not include acquired fund fees and expenses (‘AFFE’). AFFE are expenses incurred indirectly by other investment companies in which the Fund holds shares, are not direct costs paid by Fund shareholders, and are not used to calculate the Fund’s net asset value.
|
| Shareholder Fees Caption [Optional Text] |
Shareholder Fees
(fees paid directly from your investment)
|
| Shareholder Fees [Table] |
|
|
Class A |
Class I |
|
Maximum Sales Charge (Load) Imposed on Purchases
(as a percentage of offering price) |
4.50% |
none |
|
Maximum Deferred Sales Charge (Load)
(as a percentage of redemption proceeds or original purchase price, whichever is lower) |
none(1) |
none |
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| Operating Expenses Caption [Optional Text] |
Annual Fund Operating Expenses
(expenses that you pay each year as a percentage of the value of your investment)
|
| Annual Fund Operating Expenses [Table] |
|
|
Class A |
Class I |
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Management Fees |
0.75% |
0.75% |
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Distribution and Service (12b-1) Fees |
0.25% |
0.00% |
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Other Expenses |
0.82% |
0.45% |
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Acquired Fund Fees and Expenses |
0.01% |
0.01% |
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Total Annual Fund Operating Expenses(2) |
1.83% |
1.21% |
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Fee Waiver/Expense Reimbursement(3) |
(0.88)% |
(0.51)% |
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Total Annual Fund Operating Expenses After Fee Waiver/Expense Reimbursement(2) |
0.95% |
0.70% |
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| Expense Footnotes [Text Block] |
| (1) |
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Up to a 1.00% contingent deferred sales charge (CDSC) is imposed on redemptions of any part or all of a purchase of $1 million or more within 12 months of purchase. |
| (2) |
|
The Total Annual Fund Operating Expenses and Total Annual Fund Operating Expenses After Fee Waiver/Expense Reimbursement do not match the Ratios to Average Net Assets shown in the Financial Highlights section of the Prospectus, which reflect the operating expenses of the Fund and do not include acquired fund fees and expenses (‘AFFE’). AFFE are expenses incurred indirectly by other investment companies in which the Fund holds shares, are not direct costs paid by Fund shareholders, and are not used to calculate the Fund’s net asset value. |
| (3) |
|
Thornburg Investment Management, Inc. (“Thornburg”) has contractually agreed to waive fees and reimburse expenses incurred by the Fund so that actual Class A and Class I expenses (excluding taxes, interest expenses, acquired fund fees and expenses, brokerage commissions, borrowing costs, expenses relating to short sales, and unusual expenses such as contingency fees or litigation costs) do not exceed 0.94% and 0.69%, respectively. The agreement to waive fees and reimburse expenses may be terminated by the Fund’s Trustees at any time, but may not be terminated by Thornburg before February 1, 2027, unless Thornburg ceases to be the investment advisor of the Fund prior to that date. Thornburg may recoup amounts waived or reimbursed during the Fund’s fiscal year if, after taking the recoupment into account, the Fund’s actual expenses fall below the expense cap during that same fiscal year. |
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| Expense Example [Heading] |
Example.
|
| Expense Example Narrative [Text Block] |
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:
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| Expense Example, With Redemption [Table] |
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|
|
|
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|
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1 Year |
3 Years |
5 YEARS |
10 YEARS |
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Class A Shares |
$543 |
$918 |
$1,317 |
$2,432 |
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Class I Shares |
$72 |
$334 |
$616 |
$1,421 |
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| Portfolio Turnover [Heading] |
Portfolio Turnover.
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| Portfolio Turnover [Text Block] |
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 32.68% of the average value of its portfolio.
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| Portfolio Turnover, Rate |
32.68%
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