| Label | Element | Value |
|---|---|---|
| SIIT SMALL MID CAP EQUITY FUND | SMALL/MID CAP EQUITY FUND | ||
| Prospectus [Line Items] | oef_ProspectusLineItems | |
| Risk/Return [Heading] | oef_RiskReturnHeading | SMALL/MID CAP EQUITY FUND |
| Objective [Heading] | oef_ObjectiveHeading | Investment Goal |
| Objective, Primary [Text Block] | oef_ObjectivePrimaryTextBlock | Long-term capital appreciation. |
| 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 76% of the average value of its portfolio. |
| Portfolio Turnover, Rate | oef_PortfolioTurnoverRate | 76.00% |
| Strategy [Heading] | oef_StrategyHeading | Principal Investment Strategies |
| Strategy Narrative [Text Block] | oef_StrategyNarrativeTextBlock | Under normal circumstances, the Small/Mid Cap Equity Fund will invest at least 80% of its net assets (plus the amount of any borrowings for investment purposes) in equity securities (including common and preferred stocks) of small and medium-sized companies, exchange-traded funds (ETFs) based on small and medium-sized capitalization indexes and securities of real estate investment trusts (REITs). The Fund will invest primarily in common stocks of U.S. companies with market capitalizations in the range of companies in the Russell 2500 Index (between $6.99 million and $25.78 billion as of July 31, 2026) at the time of purchase. The market capitalization range and the composition of the Russell 2500 Index are subject to change. The Fund’s investments in equity securities may include, to a lesser extent, securities of large capitalization companies. The Fund uses a multi-manager approach, relying upon one or more sub-advisers (each, a Sub-Adviser and collectively, the Sub-Advisers) with differing investment philosophies to manage portions of the Fund’s portfolio under the general supervision of SEI Investments Management Corporation (SIMC or the Adviser). Each Sub-Adviser, in managing its portion of the Fund’s assets, generally applies a growth-oriented, a value-oriented or a blended approach to selecting investments. Growth-oriented managers generally select stocks they believe have attractive growth and appreciation potential in light of such characteristics as revenue and earnings growth, expectations from sell-side analysts and relative valuation, while value-oriented managers generally select stocks they believe are attractively valued in light of fundamental characteristics such as earnings, capital structure and/or return on invested capital. |
| Summary of Definition of Rule 35d-1 Term in Fund Name [Text Block] | fnd_NmRule35d1TermDfnSmryTextBlock | The Fund will invest primarily in common stocks of U.S. companies with market capitalizations in the range of companies in the Russell 2500 Index (between $6.99 million and $25.78 billion as of July 31, 2026) at the time of purchase. The market capitalization range and the composition of the Russell 2500 Index are subject to change. The Fund’s investments in equity securities may include, to a lesser extent, securities of large 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 upon one or more sub-advisers (each, a Sub-Adviser and collectively, the Sub-Advisers) with differing investment philosophies to manage portions of the Fund’s portfolio under the general supervision of SEI Investments Management Corporation (SIMC or the Adviser). Each Sub-Adviser, in managing its portion of the Fund’s assets, generally applies a growth-oriented, a value-oriented or a blended approach to selecting investments. Growth-oriented managers generally select stocks they believe have attractive growth and appreciation potential in light of such characteristics as revenue and earnings growth, expectations from sell-side analysts and relative valuation, while value-oriented managers generally select stocks they believe are attractively valued in light of fundamental characteristics such as earnings, capital structure and/or return on invested capital. |
| Rule 35d-1 Eighty Percent Investment Policy [Text Block] | fnd_NmRule35d1EightyPctInvstmntPlcyTextBlock | Under normal circumstances, the Small/Mid Cap Equity Fund will invest at least 80% of its net assets (plus the amount of any borrowings for investment purposes) in equity securities (including common and preferred stocks) of small and medium-sized companies, exchange-traded funds (ETFs) based on small and medium-sized capitalization indexes and securities of real estate investment trusts (REITs). |
| 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: 24.37% (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 | 16.37% |
| Highest Quarterly Return, Label [Optional Text] | oef_HighestQuarterlyReturnLabel | Best Quarter: |
| Highest Quarterly Return, Date | oef_BarChartHighestQuarterlyReturnDate | Jun. 30, 2020 |
| Highest Quarterly Return | oef_BarChartHighestQuarterlyReturn | 24.37% |
| Lowest Quarterly Return, Label [Optional Text] | oef_LowestQuarterlyReturnLabel | Worst Quarter: |
| Lowest Quarterly Return, Date | oef_BarChartLowestQuarterlyReturnDate | Mar. 31, 2020 |
| Lowest Quarterly Return | oef_BarChartLowestQuarterlyReturn | (30.34%) |
| 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 SMALL MID CAP EQUITY FUND | SMALL/MID CAP EQUITY 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 SMALL MID CAP EQUITY FUND | SMALL/MID CAP EQUITY 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 SMALL MID CAP EQUITY FUND | SMALL/MID CAP EQUITY 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 SMALL MID CAP EQUITY FUND | SMALL/MID CAP EQUITY 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 SMALL MID CAP EQUITY FUND | SMALL/MID CAP EQUITY FUND | Investment Style Risk [Member] | ||
| Prospectus [Line Items] | oef_ProspectusLineItems | |
| Risk [Text Block] | oef_RiskTextBlock | Investment Style Risk — The risk that smaller and medium capitalization securities may underperform other segments of the equity market or the equity markets as a whole. |
| SIIT SMALL MID CAP EQUITY FUND | SMALL/MID CAP EQUITY 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 SMALL MID CAP EQUITY FUND | SMALL/MID CAP EQUITY 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 SMALL MID CAP EQUITY FUND | SMALL/MID CAP EQUITY FUND | REITs Risk [Member] | ||
| Prospectus [Line Items] | oef_ProspectusLineItems | |
| Risk [Text Block] | oef_RiskTextBlock | REITs Risk — REITs are trusts that invest primarily in commercial real estate or real estate-related loans. The Fund’s investments in REITs will be subject to the risks associated with the direct ownership of real estate. Risks commonly associated with the direct ownership of real estate include fluctuations in the value of underlying properties, defaults by borrowers or tenants, changes in interest rates and risks related to general or local economic conditions. Some REITs may have limited diversification and may be subject to risks inherent in financing a limited number of properties. |
| SIIT SMALL MID CAP EQUITY FUND | SMALL/MID CAP EQUITY 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 SMALL MID CAP EQUITY FUND | SMALL/MID CAP EQUITY FUND | SIIT SMALL MID CAP EQUITY FUND - CLASS A | ||
| Prospectus [Line Items] | oef_ProspectusLineItems | |
| Management Fees (as a percentage of Assets) | oef_ManagementFeesOverAssets | 0.65% |
| 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 | 0.72% |
| Expense Example, with Redemption, 1 Year | oef_ExpenseExampleYear01 | $ 74 |
| Expense Example, with Redemption, 3 Years | oef_ExpenseExampleYear03 | 230 |
| Expense Example, with Redemption, 5 Years | oef_ExpenseExampleYear05 | 401 |
| Expense Example, with Redemption, 10 Years | oef_ExpenseExampleYear10 | $ 894 |
| SMALL/MID CAP EQUITY FUND | Russell 2500 Index Return (reflects no deduction for fees, expenses or taxes) | ||
| Prospectus [Line Items] | oef_ProspectusLineItems | |
| Average Annual Return, Label [Optional Text] | oef_AverageAnnualReturnLabel | Russell 2500 Index Return (reflects no deduction for fees, expenses or taxes) |
| Average Annual Return, Percent | oef_AvgAnnlRtrPct | 11.91% |
| Average Annual Return, Percent | oef_AvgAnnlRtrPct | 7.26% |
| Average Annual Return, Percent | oef_AvgAnnlRtrPct | 10.40% |
| Average Annual Return, Percent | oef_AvgAnnlRtrPct | 9.50% |
| SMALL/MID CAP EQUITY 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 | 10.89% |
| SMALL/MID CAP EQUITY FUND | SIIT SMALL MID CAP EQUITY FUND - CLASS A | ||
| Prospectus [Line Items] | oef_ProspectusLineItems | |
| Annual Return [Percent] | oef_AnnlRtrPct | 16.62% |
| Annual Return [Percent] | oef_AnnlRtrPct | 13.65% |
| Annual Return [Percent] | oef_AnnlRtrPct | (11.02%) |
| Annual Return [Percent] | oef_AnnlRtrPct | 25.56% |
| Annual Return [Percent] | oef_AnnlRtrPct | 12.27% |
| Annual Return [Percent] | oef_AnnlRtrPct | 26.36% |
| Annual Return [Percent] | oef_AnnlRtrPct | (17.80%) |
| Annual Return [Percent] | oef_AnnlRtrPct | 12.84% |
| Annual Return [Percent] | oef_AnnlRtrPct | 11.98% |
| Annual Return [Percent] | oef_AnnlRtrPct | 3.68% |
| Average Annual Return, Label [Optional Text] | oef_AverageAnnualReturnLabel | Return Before Taxes |
| Average Annual Return, Percent | oef_AvgAnnlRtrPct | 3.68% |
| Average Annual Return, Percent | oef_AvgAnnlRtrPct | 6.35% |
| Average Annual Return, Percent | oef_AvgAnnlRtrPct | 8.50% |
| Average Annual Return, Percent | oef_AvgAnnlRtrPct | 8.26% |
| Performance Inception Date | oef_PerfInceptionDate | Dec. 15, 2003 |
| SMALL/MID CAP EQUITY FUND | SIIT SMALL MID CAP EQUITY 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 | 1.90% |
| Average Annual Return, Percent | oef_AvgAnnlRtrPct | 3.63% |
| Average Annual Return, Percent | oef_AvgAnnlRtrPct | 5.75% |
| Average Annual Return, Percent | oef_AvgAnnlRtrPct | 6.06% |
| SMALL/MID CAP EQUITY FUND | SIIT SMALL MID CAP EQUITY 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 | 3.45% |
| Average Annual Return, Percent | oef_AvgAnnlRtrPct | 4.46% |
| Average Annual Return, Percent | oef_AvgAnnlRtrPct | 6.11% |
| Average Annual Return, Percent | oef_AvgAnnlRtrPct | 6.20% |