v3.25.2
S000003467 [Member] Average Annual Total Returns
 12 Months Ended 43 Months Ended 60 Months Ended 120 Months Ended 435 Months Ended
Mar. 31, 2025
Dec. 31, 2024
Dec. 31, 2024
Dec. 31, 2024
Dec. 31, 2024
Dec. 31, 2024
Prospectus [Line Items]            
Average Annual Return, Percent          
Bloomberg 5-Year Municipal Bond Index (reflects no deduction for fees, expenses or taxes)            
Prospectus [Line Items]            
Average Annual Return, Percent [1]   1.05%   0.99% 2.25%  
Bloomberg Municipal Bond Index (reflects no deduction for fees, expenses or taxes)            
Prospectus [Line Items]            
Average Annual Return, Percent [2]   1.17%   0.91% 1.67%  
Sit Tax-Free Income Fund - Class S            
Prospectus [Line Items]            
Average Annual Return, Percent   5.30%   69.00% 2.31%  
Performance Inception Date           Sep. 29, 1988
Sit Tax-Free Income Fund - Class S | After Taxes on Distributions            
Prospectus [Line Items]            
Average Annual Return, Percent   5.28%   0.69% 2.30%  
Performance Inception Date           Sep. 29, 1988
Sit Tax-Free Income Fund - Class S | After Taxes on Distributions and Sales            
Prospectus [Line Items]            
Average Annual Return, Percent   4.61%   1.25% 2.55%  
Performance Inception Date           Sep. 29, 1988
Sit Tax-Free Income Fund - Class Y            
Prospectus [Line Items]            
Average Annual Return, Percent   5.57%    
Performance Inception Date     Jun. 01, 2021      
[1]
A more narrowly-based index that reflects the market sectors in which the Fund invests.
[2]
A broad-based securities market index that represents the overall domestic debt markets. Effective June 30, 2024, and pursuant to regulatory requirements, the Bloomberg Municipal Bond Index replaced the Bloomberg 5‑Year Municipal Bond Index as the Fund’s primary performance benchmark to represent a broad-based securities market index. The Fund continues to use the Bloomberg 5‑Year Municipal Bond Index as an additional performance benchmark.