v3.26.1
Average Annual Total Returns
 12 Months Ended 47 Months Ended 60 Months Ended 82 Months Ended 105 Months Ended 120 Months Ended
Dec. 31, 2025
Dec. 31, 2025
Dec. 31, 2025
Dec. 31, 2025
Dec. 31, 2025
Dec. 31, 2025
MSCI World Net Total Return USD Index (reflects no deduction for fees, expenses, or U.S. taxes)            
Prospectus [Line Items]            
Average Annual Return, Percent 21.09%   12.15%   12.36% 12.17%
Bloomberg U.S. Aggregate Total Return Index Value USD (reflects no deduction for fees, expenses, or taxes)            
Prospectus [Line Items]            
Average Annual Return, Percent 7.30%   (0.36%)   1.88% 2.01%
Blended Index (reflects no deduction for fees, expenses, or U.S. taxes)            
Prospectus [Line Items]            
Average Annual Return, Percent 17.60%   9.01%   9.85% 9.73%
MSCI All Country World Net Total Return USD Index (reflects no deduction for fees, expenses, or taxes)            
Prospectus [Line Items]            
Average Annual Return, Percent 22.34% 11.67% 11.19% 12.58%    
Bloomberg Global-Aggregate Total Return Index Value Unhedged USD (reflects no deduction for fees, expenses, or taxes)            
Prospectus [Line Items]            
Average Annual Return, Percent 8.17% (1.12%) (2.15%) 0.57%    
Blended Index (reflects no deduction for fees, expenses, or U.S. taxes) [Member]            
Prospectus [Line Items]            
Average Annual Return, Percent 16.60% 6.51% 5.79% 7.84%    
Thornburg Investment Income Builder Fund - Class A            
Prospectus [Line Items]            
Average Annual Return, Percent 30.38%   13.87%     10.38%
Thornburg Investment Income Builder Fund - Class A | After Taxes on Distributions            
Prospectus [Line Items]            
Average Annual Return, Percent 27.72%   11.54%     8.26%
Thornburg Investment Income Builder Fund - Class A | After Taxes on Distributions and Sales            
Prospectus [Line Items]            
Average Annual Return, Percent 18.28%   9.86%     7.27%
Thornburg Investment Income Builder Fund - Class C            
Prospectus [Line Items]            
Average Annual Return, Percent 34.66%   14.09%     10.07%
Thornburg Investment Income Builder Fund - Class I            
Prospectus [Line Items]            
Average Annual Return, Percent 36.93%   15.21%     11.17%
Thornburg Investment Income Builder Fund - Class R6            
Prospectus [Line Items]            
Average Annual Return, Percent 37.01%   15.30%   11.35%  
Performance Inception Date         Apr. 10, 2017  
Thornburg Summit Fund - Class A            
Prospectus [Line Items]            
Average Annual Return, Percent 14.88% 7.80%        
Performance Inception Date   Jan. 26, 2022        
Thornburg Summit Fund - Class A | After Taxes on Distributions            
Prospectus [Line Items]            
Average Annual Return, Percent 12.67% 6.33%        
Thornburg Summit Fund - Class A | After Taxes on Distributions and Sales            
Prospectus [Line Items]            
Average Annual Return, Percent 9.32% 5.48%        
Thornburg Summit Fund - Class I            
Prospectus [Line Items]            
Average Annual Return, Percent 20.53%   9.41% 12.21%    
Performance Inception Date       Mar. 01, 2019