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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 82% of the average value of its portfolio.

Portfolio Turnover, Rate rr_PortfolioTurnoverRate 82.00%
Expenses Not Correlated to Ratio Due to Acquired Fund Fees [Text] rr_ExpensesNotCorrelatedToRatioDueToAcquiredFundFees Because the Fund incurred AFFE during the most recent fiscal year, the operating expenses in this fee table will not correlate to the expense ratio in the Fund's financial statements (or the "Financial Highlights" section in the prospectus) because the financial statements include only the direct operating expenses incurred by the Fund, not the indirect costs of investing in other investment companies.
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 $1.61 billion and $424.74 billion as of July 31, 2013) at the time of purchase. The market capitalization range and the composition of the Russell 1000 Index are subject to change. 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 SIMC. 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 is expected to have an absolute 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.


Certain Sub-Advisers use portfolio strategies that are designed to correlate with a portfolio of large capitalization equity securities, but which are composed of futures contracts (also called "futures") and swaps backed by other types of securities. The Fund may invest in futures and swaps either for risk management purposes or as part of its investment strategies. These portfolio strategies are included in the Fund's principal investment strategy described above. The managers may purchase futures contracts or swaps, generally using only a fraction of the assets that would be needed to purchase the equity securities directly, so that the remainder of the assets in a portfolio may be invested in other types of securities. Therefore, a Sub-Adviser would seek to outperform a large capitalization benchmark by purchasing futures contracts or swaps correlated to a broad large capitalization index and investing the remaining assets in other types of securities to add excess return. This portion of the Fund's assets may be invested in a wide range of asset classes other than large capitalization equities.


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. In addition to the obtaining synthetic exposure and mitigating risk, interest rate swaps, in particular, are also used to manage the Fund's yield spread sensitivity. In other words, by entering into interest rate swaps, the Fund can hedge the risk associated with its current investments in fixed income assets in response to changes in interest rates. When the Fund seeks to take an active long or short position with respect to the likelihood of an event of default of a security or basket of securities, the Fund may use credit default swaps. The Fund may buy credit default swaps in an attempt to manage credit risk where the Fund has credit exposure to an issuer and the Fund may sell credit default swaps to more efficiently gain credit exposure to such security or basket of securities.

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 and swaps is subject to market risk, leverage risk, correlation risk and liquidity risk. Leverage risk and liquidity risk are described below. 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 swap agreements 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.


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.


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.


Loss of money is a risk of investing in the Fund.

Risk Lose Money [Text] rr_RiskLoseMoney Loss of money is a risk of investing in the Fund.
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 six 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 six 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% (06/30/09)


Worst Quarter: -25.55% (12/31/08)


The Fund's total return from January 1, 2013 to June 30, 2013 was 13.05%.

Year to Date Return, Label rr_YearToDateReturnLabel total return
Bar Chart, Year to Date Return, Date rr_BarChartYearToDateReturnDate Jun. 30, 2013
Bar Chart, Year to Date Return rr_BarChartYearToDateReturn 13.05%
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, 2012)
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 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.

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 16.42%
Average Annual Returns, 5 Years rr_AverageAnnualReturnYear05 1.92%
Average Annual Returns, Since Inception rr_AverageAnnualReturnSinceInception 3.95%
Average Annual Returns, Inception Date rr_AverageAnnualReturnInceptionDate Feb. 28, 2006
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 0.06%
Acquired Fund Fees and Expenses (AFFE) rr_AcquiredFundFeesAndExpensesOverAssets 0.01%
Total Annual Fund Operating Expenses rr_ExpensesOverAssets 0.47% [1]
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%
Label rr_AverageAnnualReturnLabel Return Before Taxes
Average Annual Returns, 1 Year rr_AverageAnnualReturnYear01 15.97%
Average Annual Returns, 5 Years rr_AverageAnnualReturnYear05 0.18%
Average Annual Returns, Since Inception rr_AverageAnnualReturnSinceInception 2.46%
Average Annual Returns, Inception Date rr_AverageAnnualReturnInceptionDate Feb. 28, 2006
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 15.52%
Average Annual Returns, 5 Years rr_AverageAnnualReturnYear05 (0.05%)
Average Annual Returns, Since Inception rr_AverageAnnualReturnSinceInception 1.98%
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 10.64%
Average Annual Returns, 5 Years rr_AverageAnnualReturnYear05 0.09%
Average Annual Returns, Since Inception rr_AverageAnnualReturnSinceInception 1.93%
[1] Because the Fund incurred AFFE during the most recent fiscal year, the operating expenses in this fee table will not correlate to the expense ratio in the Fund's financial statements (or the "Financial Highlights" section in the prospectus) because the financial statements include only the direct operating expenses incurred by the Fund, not the indirect costs of investing in other investment companies.