Label	Element	Value
Risk Return [Abstract]	rr_RiskReturnAbstract
ProspectusDate	rr_ProspectusDate	May 31, 2012
SDIT GNMA FUND (Prospectus Summary) | SDIT GNMA FUND
Risk Return [Abstract]	rr_RiskReturnAbstract
Risk/Return, Heading	rr_RiskReturnHeading	GNMA FUND
Investment Objective, Heading	rr_ObjectiveHeading	Investment Goal
investment Objective, Primary	rr_ObjectivePrimaryTextBlock	Preserve principal value and maintain a high degree of liquidity while providing current income.
Expense, Heading	rr_ExpenseHeading	Fees and Expenses
Expense, Narrative	rr_ExpenseNarrativeTextBlock	This table describes the fees and expenses that you may pay if you buy and hold Fund shares.
Shareholder Fees, Caption	rr_ShareholderFeesCaption	SHAREHOLDER FEES (fees paid directly from your investment)
Operating Expenses, Caption	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	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 1,515% of the average value of its portfolio.
Portfolio Turnover, Rate	rr_PortfolioTurnoverRate	1515.00%
Expense Example, Heading	rr_ExpenseExampleHeading	EXAMPLE
Expense Example, Narrative	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	rr_ExpenseExampleByYearCaption	Although your actual costs may be higher or lower, based on these assumptions your costs would be:
Investment Strategy, Heading	rr_StrategyHeading	Principal Investment Strategies
Investment Strategy, Narrative	rr_StrategyNarrativeTextBlock	Under normal circumstances, the GNMA Fund invests at least 80% of its net assets (plus the amount of any borrowings for investment purposes) in mortgage-backed securities issued by the Government National Mortgage Association (GNMA). The Fund may also invest in U.S. Treasury securities and U.S. Government securities obligations, and repurchase agreements collateralized by such obligations. In addition, the Fund may enter into dollar roll transactions with selected banks and broker-dealers and invest in to-be-announced mortgage-backed securities and futures contracts. The Fund will primarily use futures contracts for hedging purposes to manage the Fund's exposure to interest rate risk. There may also be times when the Fund utilizes futures contracts to take an active position on interest rates to either increase or reduce the interest rate sensitivity of the Fund. Using a top-down strategy and bottom-up security selection, the Sub-Adviser seeks attractively-valued securities that offer competitive yields. The Sub-Adviser also considers factors such as the anticipated level of interest rates, relative valuations and yield spreads, and the duration of the Fund's entire portfolio. Duration measures the price sensitivity of a fixed income security to changes in interest rates. For example, a five year duration means that the fixed income security will decrease in value by 5% if interest rates rise 1% and increase in value by 5% if interest rates fall 1%.
Risk, Heading	rr_RiskHeading	Principal Risks
Risk, Narrative	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 involves risks different from or possibly greater than the risks associated with investing directly in securities and other traditional investments. The primary risks of futures include leverage risk, liquidity risk, market risk and correlation risk. Leverage risk, liquidity risk and market risk relating to the Fund's use of derivatives are described below. Correlation risk is the risk that changes in the value of the derivative may not correlate perfectly with the underlying asset, rate or index. Each of these risks could cause the Fund to lose more than the principal amount invested. Dollar Rolls Risk - The Fund's investments in dollar rolls may subject the Fund to leverage risk and liquidity risk, both of which are described below. Extension Risk - The risk that rising interest rates may extend the duration of a fixed income security, typically reducing the security's value. Fixed Income Market Risk - The prices of the Fund's fixed income securities respond to economic developments, particularly interest rate changes, as well as to perceptions about the creditworthiness of individual issuers, including governments and their agencies. Interest Rate Risk - The risk that the Fund's yield will decline due to falling interest rates. A rise in interest rates typically causes a fall in the value of fixed income securities in which the Fund invests, while a fall in interest rates typically causes a rise in the value of such securities. Investment Style Risk - The risk that GNMA securities may underperform other segments of the fixed income markets or the fixed income markets as a whole.    Leverage Risk - Leverage risk is the risk that a small percentage of the Fund's assets can have a disproportionately larger impact on the Fund. 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. Liquidity Risk - The risk that certain securities may be difficult or impossible to sell at the time and the price that the seller would like. The seller 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. 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 bond market as a whole. Mortgage-Backed Securities Risk - Mortgage-backed securities are affected by, among other things, interest rate changes and the possibility of prepayment of the underlying mortgage loans. Mortgage-backed securities are also subject to the risk that underlying borrowers will be unable to meet their obligations. Opportunity Risk - The risk of missing out on an investment opportunity because the assets necessary to take advantage of it are tied up in other investments. 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. Prepayment Risk - The risk that, with declining interest rates, fixed income securities with stated interest rates may have the principal paid earlier than expected, requiring the Fund to invest the proceeds at generally lower interest rates. U.S. Government Securities Risk - Although U.S. Government securities are considered to be among the safest investments, they are not guaranteed against price movements due to changing interest rates. Obligations issued by some U.S. Government agencies are backed by the U.S. Treasury, while others are backed solely by the ability of the agency to borrow from the U.S. Treasury or by the agency's own resources. Loss of money is a risk of investing in the Fund.
Risk, Lose Money	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	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 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, compared with those of a broad measure of market performance. 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	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 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, compared with those of a broad measure of market performance.
Performance, Availability Phone Number	rr_PerformanceAvailabilityPhone	1-800-DIAL-SEI
Performance, Past Does Not Indicate Future	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	rr_BarChartClosingTextBlock	Best Quarter: 4.87% (12/31/08) Worst Quarter: -1.10% (06/30/04) The Fund's Class A total return (pre-tax) from January 1, 2012 to March 31, 2012 was 0.10%.
Performance Table, Heading	rr_PerformanceTableHeading	Average Annual Total Returns (for the periods ended December 31, 2011)
Index No Deduction for Fees, Expenses, Taxes	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.
SDIT GNMA FUND (Prospectus Summary) | SDIT GNMA FUND | Barclays Capital GNMA Index Return
Risk Return [Abstract]	rr_RiskReturnAbstract
Average Annual Returns, Label	rr_AverageAnnualReturnLabel	Barclays Capital GNMA Index Return (reflects no deduction for fees, expenses or taxes)
Average Annual Returns, 1 Year	rr_AverageAnnualReturnYear01	7.90%
Average Annual Returns, 5 Years	rr_AverageAnnualReturnYear05	6.95%
Average Annual Returns, 10 Years	rr_AverageAnnualReturnYear10	5.83%
Average Annual Returns, Since Inception	rr_AverageAnnualReturnSinceInception	7.37%	[1]
Average Annual Returns, Inception Date	rr_AverageAnnualReturnInceptionDate	Mar. 20, 1987
SDIT GNMA FUND (Prospectus Summary) | SDIT GNMA FUND | CLASS A
Risk Return [Abstract]	rr_RiskReturnAbstract
Redemption Fee (applies to a redemption, or series of redemptions, from a single identifiable source that, in the aggregate, exceeds $10 million within any thirty (30) day period)	rr_RedemptionFeeOverRedemption	(0.25%)
Management Fees	rr_ManagementFeesOverAssets	0.09%
Distribution (12b-1) Fees	rr_DistributionAndService12b1FeesOverAssets	none
Other Expenses	rr_OtherExpensesOverAssets	0.61%
Total Annual Fund Operating Expenses	rr_ExpensesOverAssets	0.70%
Expense Example, With Redemption, 1 Year	rr_ExpenseExampleYear01	72
Expense Example, With Redemption, 3 Years	rr_ExpenseExampleYear03	224
Expense Example, With Redemption, 5 Years	rr_ExpenseExampleYear05	390
Expense Example, With Redemption, 10 Years	rr_ExpenseExampleYear10	871
Annual Return 2002	rr_AnnualReturn2002	8.46%
Annual Return 2003	rr_AnnualReturn2003	1.95%
Annual Return 2004	rr_AnnualReturn2004	3.63%
Annual Return 2005	rr_AnnualReturn2005	2.93%
Annual Return 2006	rr_AnnualReturn2006	4.09%
Annual Return 2007	rr_AnnualReturn2007	6.33%
Annual Return 2008	rr_AnnualReturn2008	8.45%
Annual Return 2009	rr_AnnualReturn2009	6.29%
Annual Return 2010	rr_AnnualReturn2010	7.66%
Annual Return 2011	rr_AnnualReturn2011	8.11%
Year to Date Return, Label	rr_YearToDateReturnLabel	The Fund's Class A total return (pre-tax)
Bar Chart, Year to Date Return, Date	rr_BarChartYearToDateReturnDate	Mar. 31, 2012
Bar Chart, Year to Date Return	rr_BarChartYearToDateReturn	0.10%
Highest Quarterly Return, Label	rr_HighestQuarterlyReturnLabel	Best Quarter:
Highest Quarterly Return, Date	rr_BarChartHighestQuarterlyReturnDate	Dec. 31, 2008
Highest Quarterly Return	rr_BarChartHighestQuarterlyReturn	4.87%
Lowest Quarterly Return, Label	rr_LowestQuarterlyReturnLabel	Worst Quarter:
Lowest Quarterly Return, Date	rr_BarChartLowestQuarterlyReturnDate	Jun. 30, 2004
Lowest Quarterly Return	rr_BarChartLowestQuarterlyReturn	(1.10%)
Average Annual Returns, Label	rr_AverageAnnualReturnLabel	Fund Return Before Taxes
Average Annual Returns, 1 Year	rr_AverageAnnualReturnYear01	8.11%
Average Annual Returns, 5 Years	rr_AverageAnnualReturnYear05	7.36%
Average Annual Returns, 10 Years	rr_AverageAnnualReturnYear10	5.76%
Average Annual Returns, Since Inception	rr_AverageAnnualReturnSinceInception	6.85%
Average Annual Returns, Inception Date	rr_AverageAnnualReturnInceptionDate	Mar. 20, 1987
SDIT GNMA FUND (Prospectus Summary) | SDIT GNMA FUND | CLASS A | After Taxes on Distributions
Risk Return [Abstract]	rr_RiskReturnAbstract
Average Annual Returns, Label	rr_AverageAnnualReturnLabel	Fund Return After Taxes on Distributions
Average Annual Returns, 1 Year	rr_AverageAnnualReturnYear01	6.47%
Average Annual Returns, 5 Years	rr_AverageAnnualReturnYear05	5.87%
Average Annual Returns, 10 Years	rr_AverageAnnualReturnYear10	4.08%
Average Annual Returns, Since Inception	rr_AverageAnnualReturnSinceInception	4.54%
Average Annual Returns, Inception Date	rr_AverageAnnualReturnInceptionDate	Mar. 20, 1987
SDIT GNMA FUND (Prospectus Summary) | SDIT GNMA FUND | CLASS A | After Taxes on Distributions and Sales
Risk Return [Abstract]	rr_RiskReturnAbstract
Average Annual Returns, Label	rr_AverageAnnualReturnLabel	Fund Return After Taxes on Distributions and Sale of Fund Shares
Average Annual Returns, 1 Year	rr_AverageAnnualReturnYear01	5.38%
Average Annual Returns, 5 Years	rr_AverageAnnualReturnYear05	5.45%
Average Annual Returns, 10 Years	rr_AverageAnnualReturnYear10	3.93%
Average Annual Returns, Since Inception	rr_AverageAnnualReturnSinceInception	4.48%
Average Annual Returns, Inception Date	rr_AverageAnnualReturnInceptionDate	Mar. 20, 1987

[1] Index returns are shown from March 31, 1987.