Label	Element	Value
SIIT LARGE CAP DIVERSIFIED ALPHA FUND
Risk/Return:	rr_RiskReturnAbstract
Risk/Return [Heading]	rr_RiskReturnHeading	SIIT LARGE CAP DIVERSIFIED ALPHA FUND
Objective [Heading]	rr_ObjectiveHeading	Investment Goal
Objective, Primary [Text Block]	rr_ObjectivePrimaryTextBlock	Long-term growth of capital and income.
Expense [Heading]	rr_ExpenseHeading	Fees and Expenses
Expense Narrative [Text Block]	rr_ExpenseNarrativeTextBlock	This table describes the fees and expenses that you may pay if you buy and hold Fund shares.
Operating Expenses Caption [Text]	rr_OperatingExpensesCaption	ANNUAL FUND OPERATING EXPENSES (expenses that you pay each year as a percentage of the value of your investment)
Portfolio Turnover [Heading]	rr_PortfolioTurnoverHeading	PORTFOLIO TURNOVER
Portfolio Turnover [Text Block]	rr_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 110% of the average value of its portfolio.
Portfolio Turnover, Rate	rr_PortfolioTurnoverRate	110.00%
Expense Example [Heading]	rr_ExpenseExampleHeading	EXAMPLE
Expense Example Narrative [Text Block]	rr_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 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]	rr_ExpenseExampleByYearCaption	Although your actual costs and returns may be higher or lower, based on these assumptions your costs would be:
Strategy [Heading]	rr_StrategyHeading	Principal Investment Strategies
Strategy Narrative [Text Block]	rr_StrategyNarrativeTextBlock	Under normal circumstances, the Large Cap Diversified Alpha 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 $1.05 billion and $692 billion as of July 31, 2015) at the time of purchase. The market capitalization range and the composition of the Russell 1000 Index are subject to change. In some instances, the securities that compose the Russell 1000 Index are foreign securities or represent exposure to foreign markets. The Fund may also, to a lesser extent, invest in common and preferred stocks of small capitalization companies. The Fund may also invest in ETFs based on a large capitalization index. The Fund uses a multi-manager approach under the general supervision of SEI Investments Management Corporation (SIMC or the Adviser). SIMC allocates most of the Fund's assets among multiple Sub-Advisers that use different investment strategies to seek to achieve returns in excess of the performance of the Russell 1000 Index. Assets of the Fund not allocated to Sub-Advisers are managed directly by SIMC. This allocation among investment strategies aims to diversify the sources from which the Fund seeks to achieve excess returns (i.e., returns in excess of a benchmark index or "alpha"), thereby diversifying the relative risk of the Fund. While the Fund seeks to have a return and risk profile similar to the broad U.S. large capitalization equity market, returns may be derived in part from investing up to 20% of the Fund in securities outside of the large capitalization market. The Fund implements the investment recommendations of its Sub-Advisers through the use of an overlay manager appointed by SIMC. Each Sub-Adviser provides a model portfolio to the Fund on an ongoing basis that represents that Sub-Adviser's recommendation as to the securities to be purchased, sold or retained by the Fund. The overlay manager then constructs a portfolio for the Fund that represents the aggregation of the model portfolios of the Sub-Advisers and SIMC, with the weighting of each model in the total portfolio determined by SIMC. Pursuant to direction from SIMC, the overlay manager has limited authority to vary from the models. For example, SIMC may direct the overlay manager to adjust the portfolio to implement SIMC's forward-looking views regarding various portfolio characteristics or factors, or for risk management purposes. This may include favoring securities of companies that are more highly ranked with respect to environmental, social and governance criteria than other companies in the Fund's portfolio. The overlay manger may also vary the portfolio implementation to seek trading cost efficiencies, loss harvesting, portfolio rebalancing or other portfolio construction objectives directed by SIMC. The Fund may also invest in futures contracts and swaps for speculative or hedging purposes. Futures and swaps are used to synthetically obtain exposure to securities or baskets of securities. These derivatives are also used to mitigate the Fund's overall level of risk and/or the Fund's risk to particular types of securities or market segments. The Fund may buy and sell securities frequently as a result of its investment strategy.
Risk [Heading]	rr_RiskHeading	Principal Risks
Risk Narrative [Text Block]	rr_RiskNarrativeTextBlock	Credit Risk — The risk that the issuer of a security or the counterparty to a contract will default or otherwise become unable to honor a financial obligation. Derivatives Risk — The Fund's use of futures contracts and swaps is subject to market risk, leverage risk, correlation risk and liquidity risk. Leverage risk and liquidity risk are described below. Many over-the-counter ("OTC") derivative instruments will not have liquidity beyond the counterparty to the instrument. Market risk is the risk that the market value of an investment may move up and down, sometimes rapidly and unpredictably. 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 swaps is also subject to credit risk and valuation risk. Valuation risk is the risk that the derivative may be difficult to value and/or valued incorrectly. Credit risk is described above. Each of these risks could cause the Fund to lose more than the principal amount invested in a derivative instrument. Some derivatives have the potential for unlimited loss, regardless of the size of the Fund's initial investment. The other parties to certain derivative contracts present the same types of credit risk as issuers of fixed income securities. The Fund's use of derivatives may also increase the amount of taxes payable by shareholders. Recent legislation calls for new regulation of the derivatives markets. The extent and impact of the regulation are not yet fully known and may not be for some time. New regulation of derivatives may make them more costly, may limit their availability or may otherwise adversely affect their value or performance. Equity Market Risk — The risk that stock prices will fall over short or extended periods of time. Exchange-Traded Funds (ETFs) 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. 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 and tax environments. Investment Style Risk — The risk that large capitalization securities may underperform other segments of the equity markets or the equity markets as a whole. The Fund uses portfolio strategies that are designed to correlate with a portfolio of large capitalization equity securities, but which are composed of derivative instruments backed by other types of securities in order to seek to generate excess return. The financial performance of the Fund will be affected, positively or negatively, by the financial performance of the securities backing such derivative instruments. These factors, among others, may cause the Fund to perform differently than a fund that is invested solely in large capitalization equity securities or other funds with similar investment objectives or cause the Fund to underperform its benchmark. 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. 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, sell other securities instead or forego an investment opportunity, any of which could have a negative effect on Fund management or performance. Portfolio Turnover Risk — Due to its investment strategy, the Fund may buy and sell securities frequently. This may result in higher transaction costs and additional capital gains tax liabilities. Small and Medium Capitalization Risk — The risk that small and medium capitalization companies in which the Fund invests 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 or listed on an exchange. Investing in the Fund involves risk, and there is no guarantee that the Fund will achieve its investment goal. You could lose money on your investment in the Fund, just as you could with other investments.
Risk Lose Money [Text]	rr_RiskLoseMoney	You could lose money on your investment in the Fund, just as you could with other investments.
Bar Chart and Performance Table [Heading]	rr_BarChartAndPerformanceTableHeading	Performance Information
Performance Narrative [Text Block]	rr_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 eight years, and by showing how the Fund's average annual returns for 1 year, 5 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]	rr_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 eight years, and by showing how the Fund's average annual returns for 1 year, 5 years, and since the Fund's inception compare with those of a broad measure of market performance.
Performance Availability Phone [Text]	rr_PerformanceAvailabilityPhone	1-800-DIAL-SEI
Performance Past Does Not Indicate Future [Text]	rr_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]	rr_BarChartClosingTextBlock	Best Quarter: 17.00% (6/30/09) Worst Quarter: -25.55% (12/31/08) The Fund's total return from January 1, 2015 to June 30, 2015 was 1.77%.
Year to Date Return, Label	rr_YearToDateReturnLabel	total return
Bar Chart, Year to Date Return, Date	rr_BarChartYearToDateReturnDate	Jun. 30, 2015
Bar Chart, Year to Date Return	rr_BarChartYearToDateReturn	1.77%
Highest Quarterly Return, Label	rr_HighestQuarterlyReturnLabel	Best Quarter:
Highest Quarterly Return, Date	rr_BarChartHighestQuarterlyReturnDate	Jun. 30, 2009
Highest Quarterly Return	rr_BarChartHighestQuarterlyReturn	17.00%
Lowest Quarterly Return, Label	rr_LowestQuarterlyReturnLabel	Worst Quarter:
Lowest Quarterly Return, Date	rr_BarChartLowestQuarterlyReturnDate	Dec. 31, 2008
Lowest Quarterly Return	rr_BarChartLowestQuarterlyReturn	(25.55%)
Performance Table Heading	rr_PerformanceTableHeading	Average Annual Total Returns (for the periods ended December 31, 2014)
Index No Deduction for Fees, Expenses, Taxes [Text]	rr_IndexNoDeductionForFeesExpensesTaxes	(reflects no deduction for fees, expenses or taxes)
Performance Table Uses Highest Federal Rate	rr_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	rr_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 Explanation after Tax Higher	rr_PerformanceTableExplanationAfterTaxHigher	In the event of negative performance, the Fund's returns after taxes on distributions and sale of Fund Shares are calculated assuming that an investor has sufficient capital gains of the same character from other investments to offset any capital losses from the sale of Fund Shares. As a result, the Fund's returns after taxes on distributions and sale of Fund Shares may exceed the Fund's returns before taxes and/or returns after taxes on distributions.
Performance Table Narrative	rr_PerformanceTableNarrativeTextBlock	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. In the event of negative performance, the Fund's returns after taxes on distributions and sale of Fund Shares are calculated assuming that an investor has sufficient capital gains of the same character from other investments to offset any capital losses from the sale of Fund Shares. As a result, the Fund's returns after taxes on distributions and sale of Fund Shares may exceed the Fund's returns before taxes and/or returns after taxes on distributions.
SIIT LARGE CAP DIVERSIFIED ALPHA FUND \| Russell 1000 Index Return (reflects no deduction for fees, expenses or taxes)
Risk/Return:	rr_RiskReturnAbstract
Label	rr_AverageAnnualReturnLabel	Russell 1000 Index Return (reflects no deduction for fees, expenses or taxes)
Average Annual Returns, 1 Year	rr_AverageAnnualReturnYear01	13.24%
Average Annual Returns, 5 Years	rr_AverageAnnualReturnYear05	15.64%
Average Annual Returns, Since Inception	rr_AverageAnnualReturnSinceInception	7.94%
Average Annual Returns, Inception Date	rr_AverageAnnualReturnInceptionDate	Feb. 28, 2006
SIIT LARGE CAP DIVERSIFIED ALPHA FUND \| SIIT LARGE CAP DIVERSIFIED ALPHA FUND - CLASS A
Risk/Return:	rr_RiskReturnAbstract
Management Fees	rr_ManagementFeesOverAssets	0.40%
Distribution (12b-1) Fees	rr_DistributionAndService12b1FeesOverAssets	none
Other Expenses	rr_OtherExpensesOverAssets	0.07%
Total Annual Fund Operating Expenses	rr_ExpensesOverAssets	0.47%
Expense Example, with Redemption, 1 Year	rr_ExpenseExampleYear01	$ 48
Expense Example, with Redemption, 3 Years	rr_ExpenseExampleYear03	151
Expense Example, with Redemption, 5 Years	rr_ExpenseExampleYear05	263
Expense Example, with Redemption, 10 Years	rr_ExpenseExampleYear10	$ 591
Annual Return 2007	rr_AnnualReturn2007	5.35%
Annual Return 2008	rr_AnnualReturn2008	(42.67%)
Annual Return 2009	rr_AnnualReturn2009	29.39%
Annual Return 2010	rr_AnnualReturn2010	14.72%
Annual Return 2011	rr_AnnualReturn2011	2.27%
Annual Return 2012	rr_AnnualReturn2012	15.97%
Annual Return 2013	rr_AnnualReturn2013	33.66%
Annual Return 2014	rr_AnnualReturn2014	13.02%
Label	rr_AverageAnnualReturnLabel	Return Before Taxes
Average Annual Returns, 1 Year	rr_AverageAnnualReturnYear01	13.02%
Average Annual Returns, 5 Years	rr_AverageAnnualReturnYear05	15.50%
Average Annual Returns, Since Inception	rr_AverageAnnualReturnSinceInception	6.77%
Average Annual Returns, Inception Date	rr_AverageAnnualReturnInceptionDate	Feb. 28, 2006
SIIT LARGE CAP DIVERSIFIED ALPHA FUND \| SIIT LARGE CAP DIVERSIFIED ALPHA FUND - CLASS A \| After Taxes on Distributions
Risk/Return:	rr_RiskReturnAbstract
Label	rr_AverageAnnualReturnLabel	Return After Taxes on Distributions
Average Annual Returns, 1 Year	rr_AverageAnnualReturnYear01	12.02%
Average Annual Returns, 5 Years	rr_AverageAnnualReturnYear05	15.04%
Average Annual Returns, Since Inception	rr_AverageAnnualReturnSinceInception	6.24%
SIIT LARGE CAP DIVERSIFIED ALPHA FUND \| SIIT LARGE CAP DIVERSIFIED ALPHA FUND - CLASS A \| After Taxes on Distributions and Sale of Fund Shares
Risk/Return:	rr_RiskReturnAbstract
Label	rr_AverageAnnualReturnLabel	Return After Taxes on Distributions and Sale of Fund Shares
Average Annual Returns, 1 Year	rr_AverageAnnualReturnYear01	7.97%
Average Annual Returns, 5 Years	rr_AverageAnnualReturnYear05	12.46%
Average Annual Returns, Since Inception	rr_AverageAnnualReturnSinceInception	5.31%

If the Fund has annual returns for at least one calendar year, provide a bar chart showing the Fund's annual total returns for each of the last 10 calendar years (or for the life of the Fund if less than 10 years), but only for periods subsequent to the effective date of the Fund's registration statement. Present the corresponding numerical return adjacent to each bar. If the Fund's fiscal year is other than a calendar year, include the year-to-date return information as of the end of the most recent quarter in a footnote to the bar chart. Following the bar chart, disclose the Fund's highest and lowest return for a quarter during the 10 years or other period of the bar chart. When a Multiple Class Fund offers more than one Class in the prospectus, provide annual total returns in the bar chart for only one of those Classes. The Fund can select which Class to include (e.g., the oldest Class, the Class with the greatest net assets).

Reference 1: http://www.xbrl.org/2003/role/presentationRef

-Publisher SEC

-Name Form

-Number N-1A

-Chapter A

-Section 4

-Subsection b

-Paragraph 2

-Subparagraph instructions

-Clause 3

-Exhibit a