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Risk/Return: rr_RiskReturnAbstract  
Registrant Name dei_EntityRegistrantName DFA INVESTMENT DIMENSIONS GROUP INC
Prospectus Date rr_ProspectusDate Nov. 21, 2011
DFA World ex U.S. Government Fixed Income Portfolio | Institutional Class
 
Risk/Return: rr_RiskReturnAbstract  
Shareholder Fees (fees paid directly from your investment) rr_MaximumAccountFee none
Management Fee rr_ManagementFeesOverAssets 0.18%
Other Expenses rr_OtherExpensesOverAssets 0.12% [1]
Total Annual Fund Operating Expenses rr_ExpensesOverAssets 0.30%
Fee Waiver and/or Expense Reimbursement or (Recovery) rr_FeeWaiverOrReimbursementOverAssets 0.10% [2]
Total Annual Fund Operating Expenses After Fee Waiver and/or Expense Reimbursement or (Recovery) rr_NetExpensesOverAssets 0.20%
1 Year rr_ExpenseExampleYear01 20
3 Years rr_ExpenseExampleYear03 86
DFA World ex U.S. Government Fixed Income 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
Other Expenses, New Fund, Based on Estimates [Text] rr_OtherExpensesNewFundBasedOnEstimates The is a new portfolio, so the "Other Expenses" shown are based on anticipated fees and expenses for the current fiscal year
Expense Example [Heading] rr_ExpenseExampleHeading
Expense Example Narrative [Text Block] rr_ExpenseExampleNarrativeTextBlock
Strategy [Heading] rr_StrategyHeading
Strategy Narrative [Text Block] rr_StrategyNarrativeTextBlock
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.
Risk Nondiversified Status [Text] rr_RiskNondiversifiedStatus
Bar Chart and Performance Table [Heading] rr_BarChartAndPerformanceTableHeading
Performance Narrative [Text Block] rr_PerformanceNarrativeTextBlock
Performance One Year or Less [Text] rr_PerformanceOneYearOrLess Performance information is not available for the Portfolio because it has not yet commenced operations.
Performance Availability Website Address [Text] rr_PerformanceAvailabilityWebSiteAddress www.dimensional.com
[1] The is a new portfolio, so the "Other Expenses" shown are based on anticipated fees and expenses for the current fiscal year.
[2] Pursuant to a Fee Waiver and Expense Assumption Agreement for the Portfolio, the Advisor has agreed to waive all or a portion of its management fee and assume the ordinary operating expenses of a class of the Portfolio (excluding the expenses the Portfolio incurs indirectly through investment in other investment companies and excluding any applicable 12b-1 fees) ("Portfolio Expenses") to the extent necessary to limit the Portfolio Expenses of a class of the Portfolio to 0.20% of the average net assets of a class of the Portfolio on an annualized basis (the "Expense Limitation Amount"). At any time that the Portfolio Expenses are less than the Expense Limitation Amount of a class of shares of the Portfolio, the Advisor retains the right to seek reimbursement for any fees previously waived and/or expenses previously assumed to the extent that such reimbursement will not cause the annualized Portfolio Expenses for such class of shares of the Portfolio to exceed the Expense Limitation Amount. The Portfolio is not obligated to reimburse the Advisor for fees previously waived by the Advisor more than thirty-six months before the date of such reimbursement. The Fee Waiver and Expense Assumption Agreement for the Portfolio will remain in effect through February 28, 2013, and may not be terminated by the Advisor prior to that date.