v3.26.1
Expense Example
Aug. 20, 2026
USD ($)
Thornburg Investment Income Builder Fund - Class A  
Prospectus [Line Items]  
Expense Example, with Redemption, 1 Year $ 562
Expense Example, with Redemption, 3 Years 799
Expense Example, with Redemption, 5 Years 1,054
Expense Example, with Redemption, 10 Years 1,785
Thornburg Investment Income Builder Fund - Class C  
Prospectus [Line Items]  
Expense Example, with Redemption, 1 Year 293
Expense Example, with Redemption, 3 Years 597
Expense Example, with Redemption, 5 Years 1,026
Expense Example, with Redemption, 10 Years 2,222
Thornburg Investment Income Builder Fund - Class I  
Prospectus [Line Items]  
Expense Example, with Redemption, 1 Year 93
Expense Example, with Redemption, 3 Years 290
Expense Example, with Redemption, 5 Years 504
Expense Example, with Redemption, 10 Years 1,120
Thornburg Investment Income Builder Fund - Class R6  
Prospectus [Line Items]  
Expense Example, with Redemption, 1 Year 85
Expense Example, with Redemption, 3 Years 269
Expense Example, with Redemption, 5 Years 469
Expense Example, with Redemption, 10 Years 1,047
Thornburg Summit Fund - Class A  
Prospectus [Line Items]  
Expense Example, with Redemption, 1 Year 543
Expense Example, with Redemption, 3 Years 918
Expense Example, with Redemption, 5 Years 1,317
Expense Example, with Redemption, 10 Years 2,432
Thornburg Summit Fund - Class I  
Prospectus [Line Items]  
Expense Example, with Redemption, 1 Year 72
Expense Example, with Redemption, 3 Years 334
Expense Example, with Redemption, 5 Years 616
Expense Example, with Redemption, 10 Years $ 1,421