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Label Element Value
Risk/Return: rr_RiskReturnAbstract  
ProspectusDate rr_ProspectusDate May 31, 2011
SDIT GNMA FUND (Prospectus Summary) | SDIT GNMA FUND
  
Risk/Return: 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
1,024% of the average value of its portfolio.
Portfolio Turnover, Rate rr_PortfolioTurnoverRate 1024.00%
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
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 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 add 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 with acceptable maturities 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 
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. In the case of foreign securities, price
fluctuations will reflect international economic and political events, as well
as changes in currency valuations relative to the U.S. dollar.

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.

U.S. Government Securities Risk - Although the 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.

The Fund is also subject to the following additional risks:

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 derivative instruments involves risks
different from or possibly greater than the risks associated with investing
directly in securities and other traditional investments. The primary risk of
derivative instruments is that changes in the market value of securities held by
the Fund, and of the derivative instruments relating to those securities, may
not be proportionate. The Fund's use of derivatives is subject to liquidity
risk, market risk, leverage risk and correlation risk. The liquidity and market
risks relating to the Fund's use of derivatives are discussed elsewhere in this
section. Leverage risk is the risk that a small percentage of assets invested in
derivatives can have a disproportionately larger impact on the Fund. Correlation
risk is the risk that changes in the value of the derivative may not correlate
perfectly with the underlying asset, rate or index. These risks could cause
the Fund to lose more than the principal amount invested. The primary risks
of futures include leverage risk, market risk, correlation risk and liquidity risk.

Dollar Rolls Risk - The Fund's investments in dollar rolls may subject the Fund
to leverage risk and liquidity risk, both of which are discussed elsewhere in
this section.

Extension Risk - The risk that rising interest rates may extend the duration of
a fixed income security, typically reducing the security's value.

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 interests may have the principal paid earlier than
expected, requiring the Fund to invest the proceeds at generally lower interest
rates.

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 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 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, 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, Narrative rr_BarChartNarrativeTextBlock 
This bar chart shows changes in the performance of the Fund's Class A Shares
from year to year for the last ten years. The performance information shown is
based on full calendar years.
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 from January 1, 2011 to March 31, 2011 was
0.66%.
Performance Table, Heading rr_PerformanceTableHeading Average Annual Total Returns (for the periods ended December 31, 2010)
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 | CLASS A
  
Risk/Return: rr_RiskReturnAbstract  
Year to Date Return, Label rr_YearToDateReturnLabel The Fund's Class A total return from January 1, 2011 to March 31, 2011
Bar Chart, Year to Date Return, Date rr_BarChartYearToDateReturnDate Mar. 31, 2011
Bar Chart, Year to Date Return rr_BarChartYearToDateReturn 0.66%
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%)
SDIT GNMA FUND | Barclays Capital GNMA Index Return
  
Risk/Return: 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 6.67%
Average Annual Returns, 5 Years rr_AverageAnnualReturnYear05 6.29%
Average Annual Returns, 10 Years rr_AverageAnnualReturnYear10 5.86%
Average Annual Returns, Since Inception rr_AverageAnnualReturnSinceInception 7.34% [1]
Average Annual Returns, Inception Date rr_AverageAnnualReturnInceptionDate Mar. 20, 1987
SDIT GNMA FUND | CLASS A
  
Risk/Return: 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 2001 rr_AnnualReturn2001 7.61%
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%
Average Annual Returns, Label rr_AverageAnnualReturnLabel Fund Return Before Taxes
Average Annual Returns, 1 Year rr_AverageAnnualReturnYear01 7.66%
Average Annual Returns, 5 Years rr_AverageAnnualReturnYear05 6.55%
Average Annual Returns, 10 Years rr_AverageAnnualReturnYear10 5.72%
Average Annual Returns, Since Inception rr_AverageAnnualReturnSinceInception 6.83% [1]
Average Annual Returns, Inception Date rr_AverageAnnualReturnInceptionDate Mar. 20, 1987
SDIT GNMA FUND | CLASS A | After Taxes on Distributions
  
Risk/Return: rr_RiskReturnAbstract  
Average Annual Returns, Label rr_AverageAnnualReturnLabel Fund Return After Taxes on Distributions
Average Annual Returns, 1 Year rr_AverageAnnualReturnYear01 6.58%
Average Annual Returns, 5 Years rr_AverageAnnualReturnYear05 5.02%
Average Annual Returns, 10 Years rr_AverageAnnualReturnYear10 3.96%
Average Annual Returns, Since Inception rr_AverageAnnualReturnSinceInception 4.46% [1]
Average Annual Returns, Inception Date rr_AverageAnnualReturnInceptionDate Mar. 20, 1987
SDIT GNMA FUND | CLASS A | After Taxes on Distributions and Sales
  
Risk/Return: 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 5.06%
Average Annual Returns, 5 Years rr_AverageAnnualReturnYear05 4.71%
Average Annual Returns, 10 Years rr_AverageAnnualReturnYear10 3.83%
Average Annual Returns, Since Inception rr_AverageAnnualReturnSinceInception 4.41% [1]
Average Annual Returns, Inception Date rr_AverageAnnualReturnInceptionDate Mar. 20, 1987
[1] Index returns are shown from March 31, 1987.