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Label Element Value
Risk/Return: rr_RiskReturnAbstract  
Registrant Name dei_EntityRegistrantName DFA INVESTMENT DIMENSIONS GROUP INC
Prospectus Date rr_ProspectusDate Feb. 28, 2012
DFA Short-Term Extended Quality Portfolio | Institutional Class
 
Risk/Return: rr_RiskReturnAbstract  
Shareholder Fees (fees paid directly from your investment) rr_MaximumAccountFee none
Management Fee rr_ManagementFeesOverAssets 0.20%
Other Expenses rr_OtherExpensesOverAssets 0.03%
Total Annual Fund Operating Expenses rr_ExpensesOverAssets 0.23%
Fee Waiver and/or Expense Reimbursement or (Recovery) rr_FeeWaiverOrReimbursementOverAssets 0.01% [1]
Total Annual Fund Operating Expenses After Fee Waiver and/or Expense Reimbursement or (Recovery) rr_NetExpensesOverAssets 0.22%
1 Year rr_ExpenseExampleYear01 23
3 Years rr_ExpenseExampleYear03 73
5 Years rr_ExpenseExampleYear05 129
10 Years rr_ExpenseExampleYear10 292
Annual Return 2010 rr_AnnualReturn2010 5.15%
Annual Return 2011 rr_AnnualReturn2011 2.93%
Highest Quarterly Return, Label rr_HighestQuarterlyReturnLabel Highest Quarter
Highest Quarterly Return, Date rr_BarChartHighestQuarterlyReturnDate Sep. 30, 2010
Highest Quarterly Return rr_BarChartHighestQuarterlyReturn 2.42%
Lowest Quarterly Return, Label rr_LowestQuarterlyReturnLabel Lowest Quarter
Lowest Quarterly Return, Date rr_BarChartLowestQuarterlyReturnDate Dec. 31, 2010
Lowest Quarterly Return rr_BarChartLowestQuarterlyReturn (0.67%)
One Year rr_AverageAnnualReturnYear01 2.93%
Since Inception rr_AverageAnnualReturnSinceInception 5.58%
Inception Date rr_AverageAnnualReturnInceptionDate Mar. 04, 2009
DFA Short-Term Extended Quality Portfolio | Institutional Class | Return After Taxes on Distributions
 
Risk/Return: rr_RiskReturnAbstract  
One Year rr_AverageAnnualReturnYear01 2.10%
Since Inception rr_AverageAnnualReturnSinceInception 4.55%
Inception Date rr_AverageAnnualReturnInceptionDate Mar. 04, 2009
DFA Short-Term Extended Quality Portfolio | Institutional Class | Return After Taxes on Distributions and Sale of Portfolio Shares
 
Risk/Return: rr_RiskReturnAbstract  
One Year rr_AverageAnnualReturnYear01 1.94%
Since Inception rr_AverageAnnualReturnSinceInception 4.17%
Inception Date rr_AverageAnnualReturnInceptionDate Mar. 04, 2009
DFA Short-Term Extended Quality Portfolio
 
Risk/Return: rr_RiskReturnAbstract  
Risk/Return [Heading] rr_RiskReturnHeading
Objective [Heading] rr_ObjectiveHeading
Objective, Primary [Text Block] rr_ObjectivePrimaryTextBlock
Expense [Heading] rr_ExpenseHeading
Expense Narrative [Text Block] rr_ExpenseNarrativeTextBlock
Shareholder Fees Caption [Text] rr_ShareholderFeesCaption
Operating Expenses Caption [Text] rr_OperatingExpensesCaption
Fee Waiver or Reimbursement over Assets, Date of Termination rr_FeeWaiverOrReimbursementOverAssetsDateOfTermination February 28, 2013
Portfolio Turnover [Heading] rr_PortfolioTurnoverHeading
Portfolio Turnover [Text Block] rr_PortfolioTurnoverTextBlock
Portfolio Turnover, Rate rr_PortfolioTurnoverRate 17.00%
Expense Example [Heading] rr_ExpenseExampleHeading
Expense Example Narrative [Text Block] rr_ExpenseExampleNarrativeTextBlock
Strategy [Heading] rr_StrategyHeading
Strategy Narrative [Text Block] rr_StrategyNarrativeTextBlock
Strategy Portfolio Concentration [Text] rr_StrategyPortfolioConcentration The Portfolio will concentrate its assets (invest more than 25% of its total assets) in obligations of U.S. and/or foreign banks and bank holding companies ("banking industry securities") when the yield to maturity on eligible portfolio investments in banking industry securities as a group generally exceeds the yield to maturity on all other eligible portfolio investments as a group generally for a period of five consecutive days when the New York Stock Exchange is open for trading.
Risk [Heading] rr_RiskHeading
Risk Narrative [Text Block] rr_RiskNarrativeTextBlock
Risk Lose Money [Text] rr_RiskLoseMoney Because the value of your investment in the Portfolio will fluctuate, there is the risk that you will lose money.
Bar Chart and Performance Table [Heading] rr_BarChartAndPerformanceTableHeading
Performance Narrative [Text Block] rr_PerformanceNarrativeTextBlock
Performance Information Illustrates Variability of Returns [Text] rr_PerformanceInformationIllustratesVariabilityOfReturns The bar chart and table immediately following illustrate the variability of the Short-Term Extended Quality Portfolio's returns and are meant to provide some indication of the risks of investing in the Portfolio. The bar chart shows the changes in the Portfolio's performance from year to year.
Performance Availability Website Address [Text] rr_PerformanceAvailabilityWebSiteAddress www.dimensional.com
Performance Past Does Not Indicate Future [Text] rr_PerformancePastDoesNotIndicateFuture The Portfolio's past performance (before and after taxes) is not an indication of future results.
Bar Chart [Heading] rr_BarChartHeading
Bar Chart Closing [Text Block] rr_BarChartClosingTextBlock
Performance Table Heading rr_PerformanceTableHeading
Performance Table Uses Highest Federal Rate rr_PerformanceTableUsesHighestFederalRate The after-tax returns presented in the table for the Short-Term Extended Quality Portfolio 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 In addition, the after-tax returns shown are not relevant to investors who hold shares of the Portfolio through tax-deferred arrangements, such as 401(k) plans or individual retirement accounts.
DFA Short-Term Extended Quality Portfolio | BofA Merrill Lynch 1-5 Year US Corporate & Government Index (reflects no deduction for fees, expenses, or taxes)
 
Risk/Return: rr_RiskReturnAbstract  
One Year rr_AverageAnnualReturnYear01 3.10% [2]
Since Inception rr_AverageAnnualReturnSinceInception 4.42% [2]
[1] The Advisor has agreed to waive certain fees and in certain instances, assume certain expenses of the Short-Term Extended Quality Portfolio. The Fee Waiver and Expense Assumption Agreement for the Short-Term Extended Quality Portfolio will remain in effect through February 28, 2013, and may not be terminated by the Advisor prior to that date. Under certain circumstances, the Advisor retains the right to seek reimbursement for any fees previously waived and/or expenses previously assumed up to thirty-six months after such fee waiver and/or expense assumption.
[2] Source Merrill Lynch, used with permission. MERRILL LYNCH IS LICENSING THE MERRILL LYNCH INDICES "AS IS," MAKES NO WARRANTIES REGARDING SAME, DOES NOT GUARANTEE THE ACCURACY AND OR COMPLETENESS OF THE MERRILL LYNCH INDICES OR ANY DATA INCLUDED THEREIN OR DERIVED THEREFROM, AND ASSUMES NO LIABILITY IN CONNECTION WITH THEIR USE.