Shareholder Report |
12 Months Ended |
|---|---|
|
Mar. 31, 2026
USD ($)
Holding
| |
| Shareholder Report [Line Items] | |
| Document Type | N-CSR |
| Amendment Flag | false |
| Registrant Name | SIT U S GOVERNMENT SECURITIES FUND INC |
| Entity Central Index Key | 0000809981 |
| Entity Investment Company Type | N-1A |
| Document Period End Date | Mar. 31, 2026 |
| C000032004 | |
| Shareholder Report [Line Items] | |
| Fund Name | Sit U.S. Government Securities Fund |
| Class Name | Class S |
| No Trading Symbol [Flag] | true |
| Annual or Semi-Annual Statement [Text Block] | This annual shareholder report contains important information about Sit U.S. Government Securities Fund for the period of April 1, 2025 to March 31, 2026. |
| Shareholder Report Annual or Semi-Annual | Annual Shareholder Report |
| Additional Information [Text Block] | You can find additional information about the Fund at www.sitfunds.com/documents. You can also request this information by contacting us at 1-800-332-5580. |
| Additional Information Phone Number | 1-800-332-5580 |
| Expenses Paid, Amount | $ 82 |
| Expense Ratio, Percent | 0.80% |
| Material Change Date | Mar. 31, 2026 |
| AssetsNet | $ 196,960,227 |
| Holdings Count | Holding | 159 |
| Advisory Fees Paid, Amount | $ 408,661 |
| InvestmentCompanyPortfolioTurnover | 12.51% |
| Summary of Change Legend [Text Block] | There were no material changes to the Fund during the 12-month period ended March 31, 2026. |
| C000217198 | |
| Shareholder Report [Line Items] | |
| Fund Name | Sit U.S. Government Securities Fund |
| Class Name | Class Y |
| No Trading Symbol [Flag] | true |
| Annual or Semi-Annual Statement [Text Block] | This annual shareholder report contains important information about Sit U.S. Government Securities Fund for the period of April 1, 2025 to March 31, 2026. |
| Shareholder Report Annual or Semi-Annual | Annual Shareholder Report |
| Additional Information [Text Block] | You can find additional information about the Fund at www.sitfunds.com/documents. You can also request this information by contacting us at 1-800-332-5580. |
| Additional Information Phone Number | 1-800-332-5580 |
| Expenses Paid, Amount | $ 56 |
| Expense Ratio, Percent | 0.55% |
| Material Change Date | Mar. 31, 2026 |
| AssetsNet | $ 196,960,227 |
| Holdings Count | Holding | 159 |
| Advisory Fees Paid, Amount | $ 408,661 |
| InvestmentCompanyPortfolioTurnover | 12.51% |
| Summary of Change Legend [Text Block] | There were no material changes to the Fund during the 12-month period ended March 31, 2026. |