v3.26.3
Average Annual Total Returns
 12 Months Ended 60 Months Ended 120 Months Ended
Dec. 31, 2025
Dec. 31, 2025
Dec. 31, 2025
Russell 3000® Index (reflects no deduction for fees, expenses or taxes)      
Prospectus [Line Items]      
Average Annual Return, Percent [1] 17.15% 13.15% 14.29%
Russell 1000® Growth Index (reflects no deduction for fees, expenses or tax)      
Prospectus [Line Items]      
Average Annual Return, Percent [2] 18.56% 15.32% 18.13%
SIT LARGE CAP GROWTH FUND INC      
Prospectus [Line Items]      
Average Annual Return, Percent 15.24% 13.41% 15.74%
SIT LARGE CAP GROWTH FUND INC | After Taxes on Distributions      
Prospectus [Line Items]      
Average Annual Return, Percent 14.66% 12.49% 14.14%
SIT LARGE CAP GROWTH FUND INC | After Taxes on Distributions and Sales      
Prospectus [Line Items]      
Average Annual Return, Percent 9.43% 10.56% 12.64%
[1] A broad-based securities market index that represents the overall domestic equity markets.
[2] A more narrowly-based index that reflects the market sectors in which the Fund invests.