| Label | Element | Value |
|---|---|---|
| SIIT LARGE CAP FUND | LARGE CAP FUND | ||
| Prospectus [Line Items] | oef_ProspectusLineItems | |
| Risk/Return [Heading] | oef_RiskReturnHeading | LARGE CAP FUND |
| Objective [Heading] | oef_ObjectiveHeading | Investment Goal |
| Objective, Primary [Text Block] | oef_ObjectivePrimaryTextBlock | Long-term growth of capital and income. |
| Expense Heading [Optional Text] | oef_ExpenseHeading | Fees and Expenses |
| Expense Narrative [Text Block] | oef_ExpenseNarrativeTextBlock | This table describes the fees and expenses that you may pay if you buy, hold, and sell Fund shares. You may pay other fees, such as brokerage commissions and other fees to financial intermediaries, which are not reflected in this table and examples below. |
| Operating Expenses Caption [Optional Text] | oef_OperatingExpensesCaption | ANNUAL FUND OPERATING EXPENSES (expenses that you pay each year as a percentage of the value of your investment) |
| Expense Example [Heading] | oef_ExpenseExampleHeading | EXAMPLE |
| Expense Example Narrative [Text Block] | oef_ExpenseExampleNarrativeTextBlock | This Example is intended to help you compare the cost of investing in the Fund with the cost of investing in other mutual funds. The Example assumes that you invest $10,000 in the Fund for the time periods indicated and then redeem or hold all of your shares at the end of those periods. The Example also assumes that your investment has a 5% return each year and that the Fund’s operating expenses remain the same. |
| Expense Example by, Year, Caption [Text] | oef_ExpenseExampleByYearCaption | Although your actual costs may be higher or lower, based on these assumptions your costs would be: |
| Portfolio Turnover [Heading] | oef_PortfolioTurnoverHeading | PORTFOLIO TURNOVER |
| Portfolio Turnover [Text Block] | oef_PortfolioTurnoverTextBlock | The Fund pays transaction costs, such as commissions, when it buys and sells securities (or “turns over” its portfolio). A higher portfolio turnover rate may indicate higher transaction costs and may result in higher taxes when Fund shares are held in a taxable account. These costs, which are not reflected in annual Fund operating expenses or in the Example, affect the Fund’s performance. During the most recent fiscal year, the Fund’s portfolio turnover rate was 81% of the average value of its portfolio. |
| Portfolio Turnover, Rate | oef_PortfolioTurnoverRate | 81.00% |
| Strategy [Heading] | oef_StrategyHeading | Principal Investment Strategies |
| Strategy Narrative [Text Block] | oef_StrategyNarrativeTextBlock | Under normal circumstances, the Large Cap Fund will invest at least 80% of its net assets (plus the amount of any borrowings for investment purposes) in equity securities of large companies. For purposes of this Fund, a large company is a company with a market capitalization in the range of companies in the Russell 1000 Index (between $1.98 billion and $4.85 trillion as of July 31, 2026) at the time of purchase. The market capitalization range and the composition of the Russell 1000 Index are subject to change. These securities may include common stocks, preferred stocks, warrants and exchange-traded funds (ETFs) and may in some instances be foreign securities or represent exposure to foreign markets. The Fund may also, to a lesser extent, invest in common and preferred stocks of small and medium capitalization companies. The Fund uses a multi-manager approach, relying on a number of sub-advisers (each, a Sub-Adviser and collectively, the Sub-Advisers) with differing investment philosophies and strategies to manage portions of the Fund’s portfolio under the oversight of SEI Investments Management Corporation (SIMC or the Adviser). |
| Summary of Definition of Rule 35d-1 Term in Fund Name [Text Block] | fnd_NmRule35d1TermDfnSmryTextBlock | For purposes of this Fund, a large company is a company with a market capitalization in the range of companies in the Russell 1000 Index (between $1.98 billion and $4.85 trillion as of July 31, 2026) at the time of purchase. The market capitalization range and the composition of the Russell 1000 Index are subject to change. These securities may include common stocks, preferred stocks, warrants and exchange-traded funds (ETFs) and may in some instances be foreign securities or represent exposure to foreign markets. The Fund may also, to a lesser extent, invest in common and preferred stocks of small and medium capitalization companies. |
| Summary of Selection Criteria for Rule 35d-1 Term in Fund Name [Text Block] | fnd_NmRule35d1TermSlctnCritSmryTextBlock | The Fund uses a multi-manager approach, relying on a number of sub-advisers (each, a Sub-Adviser and collectively, the Sub-Advisers) with differing investment philosophies and strategies to manage portions of the Fund’s portfolio under the oversight of SEI Investments Management Corporation (SIMC or the Adviser). |
| Rule 35d-1 Eighty Percent Investment Policy [Text Block] | fnd_NmRule35d1EightyPctInvstmntPlcyTextBlock | Under normal circumstances, the Large Cap Fund will invest at least 80% of its net assets (plus the amount of any borrowings for investment purposes) in equity securities of large companies. |
| Bar Chart and Performance Table [Heading] | oef_BarChartAndPerformanceTableHeading | Performance Information |
| Performance Narrative [Text Block] | oef_PerformanceNarrativeTextBlock | The bar chart and the performance table below provide some indication of the risks of investing in the Fund by showing changes in the Fund’s performance from year to year for the past ten calendar years, and by showing how the Fund’s average annual returns for 1, 5 and 10 years, and since the Fund’s inception compare with those of a broad measure of market performance. The performance information shown is based on full calendar years. The Fund’s past performance (before and after taxes) is not necessarily an indication of how the Fund will perform in the future. For current performance information, please call 1‑800-DIAL-SEI. |
| Performance Information Illustrates Variability of Returns [Text] | oef_PerformanceInformationIllustratesVariabilityOfReturns | The bar chart and the performance table below provide some indication of the risks of investing in the Fund by showing changes in the Fund’s performance from year to year for the past ten calendar years, and by showing how the Fund’s average annual returns for 1, 5 and 10 years, and since the Fund’s inception compare with those of a broad measure of market performance. |
| Performance Additional Market Index [Text] | oef_PerformanceAdditionalMarketIndex | This table compares the Fund’s average annual total returns to those of a broad-based securities market index and an additional index with characteristics relevant to the Fund’s investment strategy. |
| Performance Availability Phone [Text] | oef_PerformanceAvailabilityPhone | 1‑800-DIAL-SEI |
| Performance Past Does Not Indicate Future [Text] | oef_PerformancePastDoesNotIndicateFuture | The Fund’s past performance (before and after taxes) is not necessarily an indication of how the Fund will perform in the future. |
| Bar Chart Closing [Text Block] | oef_BarChartClosingTextBlock | Best Quarter: 19.29% (6/30/20) |
| Year to Date Return, Label [Optional Text] | oef_YearToDateReturnLabel | total return |
| Bar Chart, Year to Date Return, Date | oef_BarChartYearToDateReturnDate | Jun. 30, 2026 |
| Bar Chart, Year to Date Return | oef_BarChartYearToDateReturn | 10.83% |
| Highest Quarterly Return, Label [Optional Text] | oef_HighestQuarterlyReturnLabel | Best Quarter: |
| Highest Quarterly Return, Date | oef_BarChartHighestQuarterlyReturnDate | Jun. 30, 2020 |
| Highest Quarterly Return | oef_BarChartHighestQuarterlyReturn | 19.29% |
| Lowest Quarterly Return, Label [Optional Text] | oef_LowestQuarterlyReturnLabel | Worst Quarter: |
| Lowest Quarterly Return, Date | oef_BarChartLowestQuarterlyReturnDate | Mar. 31, 2020 |
| Lowest Quarterly Return | oef_BarChartLowestQuarterlyReturn | (23.12%) |
| Performance Table Heading | oef_PerformanceTableHeading | Average Annual Total Returns (for the periods ended December 31, 2025) |
| Index No Deduction for Fees, Expenses, or Taxes [Text] | oef_IndexNoDeductionForFeesExpensesTaxes | (reflects no deduction for fees, expenses or taxes) |
| Performance Table Uses Highest Federal Rate | oef_PerformanceTableUsesHighestFederalRate | After-tax returns are calculated using the historical highest individual federal marginal income tax rates and do not reflect the impact of state and local taxes. |
| Performance Table Not Relevant to Tax Deferred | oef_PerformanceTableNotRelevantToTaxDeferred | Your actual after-tax returns will depend on your tax situation and may differ from those shown. After-tax returns shown are not relevant to investors who hold their Fund shares through tax-deferred arrangements, such as 401(k) plans or individual retirement accounts. |
| Performance Table Narrative | oef_PerformanceTableNarrativeTextBlock | This table compares the Fund’s average annual total returns to those of a broad-based securities market index and an additional index with characteristics relevant to the Fund’s investment strategy. After-tax returns are calculated using the historical highest individual federal marginal income tax rates and do not reflect the impact of state and local taxes. Your actual after-tax returns will depend on your tax situation and may differ from those shown. After-tax returns shown are not relevant to investors who hold their Fund shares through tax-deferred arrangements, such as 401(k) plans or individual retirement accounts. |
| SIIT LARGE CAP FUND | LARGE CAP FUND | Risk Lose Money [Member] | ||
| Prospectus [Line Items] | oef_ProspectusLineItems | |
| Risk [Text Block] | oef_RiskTextBlock | You could lose money on your investment in the Fund, just as you could with other investments. |
| SIIT LARGE CAP FUND | LARGE CAP FUND | Risk Not Insured [Member] | ||
| Prospectus [Line Items] | oef_ProspectusLineItems | |
| Risk [Text Block] | oef_RiskTextBlock | An investment in the Fund is not a deposit of a bank and is not insured or guaranteed by the Federal Deposit Insurance Corporation or any other government agency. |
| SIIT LARGE CAP FUND | LARGE CAP FUND | Market Risk [Member] | ||
| Prospectus [Line Items] | oef_ProspectusLineItems | |
| Risk [Text Block] | oef_RiskTextBlock | Market Risk — The risk that the market value of a security may move up and down, sometimes rapidly and unpredictably. Market risk may affect a single issuer, an industry, a sector or the equity market as a whole. Equity markets may decline significantly in response to adverse issuer, political, regulatory, market, economic or other developments that may cause broad changes in market value, public perceptions concerning these developments, and adverse investor sentiment or publicity. Similarly, environmental and public health risks, such as natural disasters, epidemics, pandemics or widespread fear that such events may occur, may impact markets adversely and cause market volatility in both the short- and long-term. |
| SIIT LARGE CAP FUND | LARGE CAP FUND | Large Capitalization Risk [Member] | ||
| Prospectus [Line Items] | oef_ProspectusLineItems | |
| Risk [Text Block] | oef_RiskTextBlock | Large Capitalization Risk — The risk that larger, more established companies may be unable to respond quickly to new competitive challenges such as changes in technology and consumer tastes. Larger companies also may not be able to attain the high growth rates of successful smaller companies. |
| SIIT LARGE CAP FUND | LARGE CAP FUND | Investment Style Risk [Member] | ||
| Prospectus [Line Items] | oef_ProspectusLineItems | |
| Risk [Text Block] | oef_RiskTextBlock | Investment Style Risk — The risk that large capitalization securities may underperform other segments of the equity markets or the equity markets as a whole. |
| SIIT LARGE CAP FUND | LARGE CAP FUND | Preferred Stock Risk [Member] | ||
| Prospectus [Line Items] | oef_ProspectusLineItems | |
| Risk [Text Block] | oef_RiskTextBlock | Preferred Stock Risk — Preferred stock represents an equity or ownership interest in an issuer that pays dividends at a specified rate and that has precedence over common stock in the payment of dividends. In the event an issuer is liquidated or declares bankruptcy, the claims of owners of bonds take precedence over the claims of those who own preferred and common stock. |
| SIIT LARGE CAP FUND | LARGE CAP FUND | Warrants Risk [Member] | ||
| Prospectus [Line Items] | oef_ProspectusLineItems | |
| Risk [Text Block] | oef_RiskTextBlock | Warrants Risk — Warrants are instruments that entitle the holder to buy an equity security at a specific price for a specific period of time. Warrants may be more speculative than other types of investments. The price of a warrant may be more volatile than the price of its underlying security, and a warrant may offer greater potential for capital appreciation as well as capital loss. A warrant ceases to have value if it is not exercised prior to its expiration date. |
| SIIT LARGE CAP FUND | LARGE CAP FUND | Exchange-Traded Funds Risk [Member] | ||
| Prospectus [Line Items] | oef_ProspectusLineItems | |
| Risk [Text Block] | oef_RiskTextBlock | Exchange-Traded Funds Risk — The risks of owning shares of an ETF generally reflect the risks of owning the underlying securities the ETF is designed to track, although lack of liquidity in an ETF could result in its value being more volatile than the underlying portfolio securities. When the Fund invests in an ETF, in addition to directly bearing the expenses associated with its own operations, it will bear a pro rata portion of the ETF’s expenses. |
| SIIT LARGE CAP FUND | LARGE CAP FUND | Foreign Investment Risk [Member] | ||
| Prospectus [Line Items] | oef_ProspectusLineItems | |
| Risk [Text Block] | oef_RiskTextBlock | Foreign Investment Risk — The risk that non-U.S. securities may be subject to additional risks due to, among other things, political, social and economic developments abroad, currency movements, and different legal, regulatory, tax, accounting and audit environments. |
| SIIT LARGE CAP FUND | LARGE CAP FUND | Currency Risk [Member] | ||
| Prospectus [Line Items] | oef_ProspectusLineItems | |
| Risk [Text Block] | oef_RiskTextBlock | Currency Risk — As a result of the Fund’s investments in securities denominated in, and/or receiving revenues in, foreign currencies, the Fund will be subject to currency risk. Currency risk is the risk that foreign currencies will decline in value relative to the U.S. dollar or, in the case of hedging positions, that the U.S. dollar will decline in value relative to the currency hedged. In either event, the dollar value of an investment in the Fund would be adversely affected. Currency exchange rates may fluctuate in response to, among other things, changes in interest rates, intervention (or failure to intervene) by U.S. or foreign governments, central banks or supranational entities, or by the imposition of currency controls or other political developments in the United States or abroad. |
| SIIT LARGE CAP FUND | LARGE CAP FUND | Small and Medium Capitalization Risk [Member] | ||
| Prospectus [Line Items] | oef_ProspectusLineItems | |
| Risk [Text Block] | oef_RiskTextBlock | Small and Medium Capitalization Risk — The risk that small and medium capitalization companies in which the Fund may invest may be more vulnerable to adverse business or economic events than larger, more established companies. In particular, small and medium capitalization companies may have limited product lines, markets and financial resources and may depend upon a relatively small management group. Therefore, small capitalization and medium capitalization stocks may be more volatile than those of larger companies. Small capitalization and medium capitalization stocks may be traded over-the-counter (OTC). OTC stocks may trade less frequently and in smaller volume than exchange listed stocks and may have more price volatility than that of exchange-listed stocks. |
| SIIT LARGE CAP FUND | LARGE CAP FUND | Derivatives Risk [Member] | ||
| Prospectus [Line Items] | oef_ProspectusLineItems | |
| Risk [Text Block] | oef_RiskTextBlock | Derivatives Risk — The Fund’s use of futures contracts is subject to leverage risk, correlation risk, liquidity risk and market risk. Leverage risk and liquidity risk are described below and market risk is described above. Correlation risk is the risk that changes in the value of the derivative may not correlate perfectly with the underlying asset, rate or index. The Fund’s use of derivatives may also increase the amount of taxes payable by shareholders. Both U.S. and non-U.S. regulators have adopted and implemented regulations governing derivatives markets, the ultimate impact of which remains unclear. |
| SIIT LARGE CAP FUND | LARGE CAP FUND | Liquidity Risk [Member] | ||
| Prospectus [Line Items] | oef_ProspectusLineItems | |
| Risk [Text Block] | oef_RiskTextBlock | Liquidity Risk — The risk that certain securities may be difficult or impossible to sell at the time and the price that the Fund would like. The Fund may have to lower the price of the security, sell other securities instead or forego an investment opportunity, any of which could have a negative effect on Fund management or performance. |
| SIIT LARGE CAP FUND | LARGE CAP FUND | Leverage Risk [Member] | ||
| Prospectus [Line Items] | oef_ProspectusLineItems | |
| Risk [Text Block] | oef_RiskTextBlock | Leverage Risk — The Fund’s use of derivatives may result in the Fund’s total investment exposure substantially exceeding the value of its portfolio securities and the Fund’s investment returns depending substantially on the performance of securities that the Fund may not directly own. The use of leverage can amplify the effects of market volatility on the Fund’s share price and may also cause the Fund to liquidate portfolio positions when it would not be advantageous to do so in order to satisfy its obligations. The Fund’s use of leverage may result in a heightened risk of investment loss. |
| SIIT LARGE CAP FUND | LARGE CAP FUND | SIIT LARGE CAP FUND - CLASS A | ||
| Prospectus [Line Items] | oef_ProspectusLineItems | |
| Management Fees (as a percentage of Assets) | oef_ManagementFeesOverAssets | 0.40% |
| Distribution and Service (12b-1) Fees | oef_DistributionAndService12b1FeesOverAssets | 0.00% |
| Other Expenses (as a percentage of Assets): | oef_OtherExpensesOverAssets | 0.07% |
| Expenses (as a percentage of Assets) | oef_ExpensesOverAssets | 0.47% |
| Expense Example, with Redemption, 1 Year | oef_ExpenseExampleYear01 | $ 48 |
| Expense Example, with Redemption, 3 Years | oef_ExpenseExampleYear03 | 151 |
| Expense Example, with Redemption, 5 Years | oef_ExpenseExampleYear05 | 263 |
| Expense Example, with Redemption, 10 Years | oef_ExpenseExampleYear10 | $ 591 |
| LARGE CAP FUND | Russell 1000 Index Return (reflects no deduction for fees, expenses or taxes) | ||
| Prospectus [Line Items] | oef_ProspectusLineItems | |
| Average Annual Return, Label [Optional Text] | oef_AverageAnnualReturnLabel | Russell 1000 Index Return (reflects no deduction for fees, expenses or taxes) |
| Average Annual Return, Percent | oef_AvgAnnlRtrPct | 17.37% |
| Average Annual Return, Percent | oef_AvgAnnlRtrPct | 13.59% |
| Average Annual Return, Percent | oef_AvgAnnlRtrPct | 14.59% |
| Average Annual Return, Percent | oef_AvgAnnlRtrPct | 10.34% |
| LARGE CAP FUND | S&P 500 Index Return (reflects no deduction for fees, expenses or taxes) | ||
| Prospectus [Line Items] | oef_ProspectusLineItems | |
| Average Annual Return, Label [Optional Text] | oef_AverageAnnualReturnLabel | S&P 500 Index Return (reflects no deduction for fees, expenses or taxes) |
| Average Annual Return, Percent | oef_AvgAnnlRtrPct | 17.88% |
| Average Annual Return, Percent | oef_AvgAnnlRtrPct | 14.42% |
| Average Annual Return, Percent | oef_AvgAnnlRtrPct | 14.82% |
| Average Annual Return, Percent | oef_AvgAnnlRtrPct | 10.18% |
| LARGE CAP FUND | SIIT LARGE CAP FUND - CLASS A | ||
| Prospectus [Line Items] | oef_ProspectusLineItems | |
| Annual Return [Percent] | oef_AnnlRtrPct | 7.04% |
| Annual Return [Percent] | oef_AnnlRtrPct | 21.11% |
| Annual Return [Percent] | oef_AnnlRtrPct | (6.39%) |
| Annual Return [Percent] | oef_AnnlRtrPct | 28.10% |
| Annual Return [Percent] | oef_AnnlRtrPct | 11.69% |
| Annual Return [Percent] | oef_AnnlRtrPct | 26.60% |
| Annual Return [Percent] | oef_AnnlRtrPct | (14.12%) |
| Annual Return [Percent] | oef_AnnlRtrPct | 19.51% |
| Annual Return [Percent] | oef_AnnlRtrPct | 21.28% |
| Annual Return [Percent] | oef_AnnlRtrPct | 17.72% |
| Average Annual Return, Label [Optional Text] | oef_AverageAnnualReturnLabel | Return Before Taxes |
| Average Annual Return, Percent | oef_AvgAnnlRtrPct | 17.72% |
| Average Annual Return, Percent | oef_AvgAnnlRtrPct | 13.16% |
| Average Annual Return, Percent | oef_AvgAnnlRtrPct | 12.41% |
| Average Annual Return, Percent | oef_AvgAnnlRtrPct | 9.32% |
| Performance Inception Date | oef_PerfInceptionDate | Jun. 14, 1996 |
| LARGE CAP FUND | SIIT LARGE CAP FUND - CLASS A | After Taxes on Distributions | ||
| Prospectus [Line Items] | oef_ProspectusLineItems | |
| Average Annual Return, Label [Optional Text] | oef_AverageAnnualReturnLabel | Return After Taxes on Distributions |
| Average Annual Return, Percent | oef_AvgAnnlRtrPct | 9.20% |
| Average Annual Return, Percent | oef_AvgAnnlRtrPct | 8.57% |
| Average Annual Return, Percent | oef_AvgAnnlRtrPct | 8.21% |
| Average Annual Return, Percent | oef_AvgAnnlRtrPct | 7.21% |
| LARGE CAP FUND | SIIT LARGE CAP FUND - CLASS A | After Taxes on Distributions and Sales | ||
| Prospectus [Line Items] | oef_ProspectusLineItems | |
| Average Annual Return, Label [Optional Text] | oef_AverageAnnualReturnLabel | Return After Taxes on Distributions and Sale of Fund Shares |
| Average Annual Return, Percent | oef_AvgAnnlRtrPct | 15.20% |
| Average Annual Return, Percent | oef_AvgAnnlRtrPct | 9.43% |
| Average Annual Return, Percent | oef_AvgAnnlRtrPct | 8.79% |
| Average Annual Return, Percent | oef_AvgAnnlRtrPct | 7.31% |