| Form N-CSR Cover | 12 Months Ended |
| Jun. 30, 2024 | |
| Shareholder Report [Line Items] | |
| Document Type | N-CSR |
| Amendment Flag | false |
| Registrant Name | SIT LARGE CAP GROWTH FUND INC |
| Entity Central Index Key | 0000356786 |
| Entity Investment Company Type | N-1A |
| Document Period End Date | Jun. 30, 2024 |
| Shareholder Report | 12 Months Ended |
| Jun. 30, 2024 USD ($) Holding | |
| Shareholder Report [Line Items] | |
| Document Type | N-CSR |
| Amendment Flag | false |
| Registrant Name | SIT LARGE CAP GROWTH FUND INC |
| Entity Central Index Key | 0000356786 |
| Entity Investment Company Type | N-1A |
| Document Period End Date | Jun. 30, 2024 |
| C000032270 | |
| Shareholder Report [Line Items] | |
| Fund Name | Sit Large Cap Growth Fund |
| Annual or Semi-Annual Statement [Text Block] | This annual shareholder report contains important information about Sit Large Cap Growth Fund for the period of July 1, 2023 to June 30, 2024. |
| 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 |
| Additional Information Phone Number | 1-800-332-5580 |
| Additional Information Email | www.sitfunds.com</span>/documents" id="sjs-B17"><span style="box-sizing: border-box; color: rgb(0, 0, 0); display: inline; flex-wrap: nowrap; font-size: 12px; font-weight: 400; grid-area: auto; line-height: 18px; margin: 0px; overflow: visible; text-align: left;">www.sitfunds.com</span>/documents |
| Expenses [Text Block] | What were the Fund’s costs for the last year? (based on a hypothetical $10,000 investment) Fund Name Costs of a $10,000 investment Costs paid as a percentage of a $10,000 investment Sit Large Cap Growth Fund $115 1.00% |
| Expenses Paid, Amount | $ 115 |
| Expense Ratio, Percent | 1% |
| Factors Affecting Performance [Text Block] | How did the Fund perform in the past 12 months and what affected its performance? For the 12-month period ended June 30, 2024, the Sit Large Cap Growth Fund returned +30.22%, underperforming the Russell 1000 ® |
| Line Graph [Table Text Block] | Sit Large Cap Growth Fund Russell 3000 ® Russell 1000 ® 6/14 $10,000 $10,000 $10,000 6/15 11,062 10,729 11,056 6/16 10,964 10,959 11,390 6/17 13,286 12,987 13,716 6/18 15,535 14,907 16,804 6/19 17,174 16,246 18,746 6/20 20,838 17,306 23,110 6/21 29,407 24,950 32,932 6/22 23,885 21,490 26,749 6/23 29,905 25,563 34,000 6/24 38,943 31,475 45,384 |
| Average Annual Return [Table Text Block] | 1 Year 5 Years 10 Years Sit Large Cap Growth Fund 30.22% 17.79% 14.56% Russell 3000 ® Footnote Reference 23.13% 14.14% 12.15% Russell 1000 ® 33.48% 19.34% 16.33% |
| Material Change Date | Jun. 30, 2024 |
| AssetsNet | $ 214,112,417 |
| Holdings Count | Holding | 63 |
| Advisory Fees Paid, Amount | $ 1,787,411 |
| InvestmentCompanyPortfolioTurnover | 11.11% |
| Additional Fund Statistics [Text Block] | Fund Statistics (as of June 30, 2024) Total Net Assets $214,112,417 # of Portfolio Holdings 63 Portfolio Turnover Rate 11.11% Investment Advisory Fees Paid $1,787,411 Weighted average market cap $1,398.8 Billion Median market cap 0 |
| Holdings [Text Block] | Top 10 Equity (% of Net Assets) Microsoft Corp. 11.5 % Apple, Inc. 10.6 NVIDIA Corp. 10.0 Alphabet, Inc. 7.4 Amazon.com, Inc. 5.7 Broadcom, Inc. 3.9 Applied Materials, Inc. 2.5 UnitedHealth Group, Inc. 2.4 Meta Platforms, Inc. 2.3 salesforce.com, Inc. 1.8 |
| Material Fund Change [Text Block] | Material Fund Changes There were no material changes to the Fund during the 12-month period ended June 30, 2024. |
| Summary of Change Legend [Text Block] | There were no material changes to the Fund during the 12-month period ended June 30, 2024. |
| Shareholder Report, Line Graph (Details) - USD ($) | 12 Months Ended | ||||||||||
| Jun. 30, 2024 | Jun. 30, 2023 | Jun. 30, 2022 | Jun. 30, 2021 | Jun. 30, 2020 | Jun. 30, 2019 | Jun. 30, 2018 | Jun. 30, 2017 | Jun. 30, 2016 | Jun. 30, 2015 | Jun. 30, 2014 | |
| C000032270 | |||||||||||
| Account Value [Line Items] | |||||||||||
| Line Graph and Table Measure Name | Sit Large Cap Growth Fund | ||||||||||
| Account Value | $ 38,943 | $ 29,905 | $ 23,885 | $ 29,407 | $ 20,838 | $ 17,174 | $ 15,535 | $ 13,286 | $ 10,964 | $ 11,062 | $ 10,000 |
| Russell 3000® Index | |||||||||||
| Account Value [Line Items] | |||||||||||
| Account Value | 31,475 | 25,563 | 21,490 | 24,950 | 17,306 | 16,246 | 14,907 | 12,987 | 10,959 | 10,729 | 10,000 |
| Russell 1000® Growth Index | |||||||||||
| Account Value [Line Items] | |||||||||||
| Account Value | $ 45,384 | $ 34,000 | $ 26,749 | $ 32,932 | $ 23,110 | $ 18,746 | $ 16,804 | $ 13,716 | $ 11,390 | $ 11,056 | $ 10,000 |
| Shareholder Report, Average Annual Return (Details) | 12 Months Ended | 60 Months Ended | 120 Months Ended |
| Jun. 30, 2024 | Jun. 30, 2024 | Jun. 30, 2024 | |
| C000032270 | |||
| Average Annual Return [Line Items] | |||
| Line Graph and Table Measure Name | Sit Large Cap Growth Fund | ||
| Without Sales Load [Member] | C000032270 | |||
| Average Annual Return [Line Items] | |||
| Average Annual Return, Percent | 30.22% | 17.79% | 14.56% |
| Russell 3000® Index | |||
| Average Annual Return [Line Items] | |||
| Average Annual Return, Percent | 23.13% | 14.14% | 12.15% |
| Russell 1000® Growth Index | |||
| Average Annual Return [Line Items] | |||
| Average Annual Return, Percent | 33.48% | 19.34% | 16.33% |
| Shareholder Report, Holdings (Details) - C000032270 | Jun. 30, 2024 |
| Microsoft Corp. | |
| Holdings [Line Items] | |
| Percent of Net Asset Value | 11.50% |
| Apple, Inc. | |
| Holdings [Line Items] | |
| Percent of Net Asset Value | 10.60% |
| NVIDIA Corp. | |
| Holdings [Line Items] | |
| Percent of Net Asset Value | 10% |
| Alphabet, Inc. | |
| Holdings [Line Items] | |
| Percent of Net Asset Value | 7.40% |
| Amazon.com, Inc. | |
| Holdings [Line Items] | |
| Percent of Net Asset Value | 5.70% |
| Broadcom, Inc. | |
| Holdings [Line Items] | |
| Percent of Net Asset Value | 3.90% |
| Applied Materials, Inc. | |
| Holdings [Line Items] | |
| Percent of Net Asset Value | 2.50% |
| UnitedHealth Group, Inc. | |
| Holdings [Line Items] | |
| Percent of Net Asset Value | 2.40% |
| Meta Platforms, Inc. | |
| Holdings [Line Items] | |
| Percent of Net Asset Value | 2.30% |
| salesforce.com, Inc. | |
| Holdings [Line Items] | |
| Percent of Net Asset Value | 1.80% |
| Software | |
| Holdings [Line Items] | |
| Percent of Net Asset Value | 30% |
| Technology Hardware, Storage & Peripherals | |
| Holdings [Line Items] | |
| Percent of Net Asset Value | 29.10% |
| Internet & Direct Marketing Retail | |
| Holdings [Line Items] | |
| Percent of Net Asset Value | 9.80% |
| Life Sciences Tools & Services | |
| Holdings [Line Items] | |
| Percent of Net Asset Value | 6.40% |
| Aerospace & Defense | |
| Holdings [Line Items] | |
| Percent of Net Asset Value | 5% |
| Health Care Providers & Services | |
| Holdings [Line Items] | |
| Percent of Net Asset Value | 2.90% |
| IT Services | |
| Holdings [Line Items] | |
| Percent of Net Asset Value | 2.50% |
| Beverages | |
| Holdings [Line Items] | |
| Percent of Net Asset Value | 2.40% |
| Capital Markets | |
| Holdings [Line Items] | |
| Percent of Net Asset Value | 9.40% |
