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Risk/Return:rr_RiskReturnAbstract 
Registrant Namedei_EntityRegistrantNameDFA INVESTMENT DIMENSIONS GROUP INC
Prospectus Daterr_ProspectusDateSep. 30, 2011
Institutional Class | DIMENSIONAL RETIREMENT EQUITY FUND II | Institutional Class
 
Risk/Return:rr_RiskReturnAbstract 
Shareholder Fees (fees paid directly from your investment)rr_MaximumAccountFee none
Management Feerr_ManagementFeesOverAssets0.30%
Other Expensesrr_OtherExpensesOverAssets0.16%[1]
Acquired Fund Fees and Expensesrr_AcquiredFundFeesAndExpensesOverAssets0.25%[2]
Total Annual Fund Operating Expensesrr_ExpensesOverAssets0.71%
Fee Waiver and/or Expense Reimbursementrr_FeeWaiverOrReimbursementOverAssets0.31%[3]
Total Annual Fund Operating Expenses after Fee Waiver and/or Expense Reimbursementrr_NetExpensesOverAssets0.40%
1 Yearrr_ExpenseExampleYear0141
3 Yearsrr_ExpenseExampleYear03 196
Institutional Class | DIMENSIONAL RETIREMENT EQUITY FUND II
 
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 Terminationrr_FeeWaiverOrReimbursementOverAssetsDateOfTerminationFebruary 28, 2013
Portfolio Turnover [Heading]rr_PortfolioTurnoverHeading
Portfolio Turnover [Text Block]rr_PortfolioTurnoverTextBlock
Other Expenses, New Fund, Based on Estimates [Text]rr_OtherExpensesNewFundBasedOnEstimatesThe Retirement Equity Portfolio is a new portfolio, so the "Other Expenses" shown are based on anticipated fees and expenses for the current fiscal year
Acquired Fund Fees and Expenses, Based on Estimates [Text]rr_AcquiredFundFeesAndExpensesBasedOnEstimatesRepresents the amount of fees and expenses anticipated to be incurred by the Retirement Equity Portfolio through its investments in other funds managed by the Advisor (the "Underlying Funds") and other investment companies 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_RiskLoseMoneyBecause 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 One Year or Less [Text]rr_PerformanceOneYearOrLessPerformance information is not available for the Retirement Equity Portfolio because it has not yet commenced operations.
Performance Availability Website Address [Text]rr_PerformanceAvailabilityWebSiteAddresswww.dimensional.com
[1] The Retirement Equity Portfolio is a new portfolio, so the "Other Expenses" shown are based on anticipated fees and expenses for the current fiscal year.
[2] Represents the amount of fees and expenses anticipated to be incurred by the Retirement Equity Portfolio through its investments in other funds managed by the Advisor (the "Underlying Funds") and other investment companies for the current fiscal year.
[3] Pursuant to a Fee Waiver and Expense Assumption Agreement for the Retirement Equity Portfolio, the Advisor has contractually agreed to waive up to the full amount of the Retirement Equity Portfolio's management fee of 0.30% to the extent necessary to offset the proportionate share of the management fees paid by the Retirement Equity Portfolio through its investment in other funds managed by the Advisor (the "Underlying Funds") (including the Portfolio's proportionate share of any management fees that an Underlying Fund paid through its investment in an affiliated cash management fund). In addition, under the Fee Waiver and Expense Assumption Agreement, the Advisor has also agreed to waive all or a portion of the management fee and to assume the expenses of a class of the Retirement Equity Portfolio to the extent necessary to reduce the ordinary operating expenses (including expenses incurred through its investment in other investment companies but excluding any applicable 12b-1 fees) ("Portfolio Expenses") of a class of the Retirement Equity Portfolio so that such Portfolio Expenses do not exceed 0.40% of the average net assets of a class of the Portfolio on an annualized basis. The Fee Waiver and Expense Assumption Agreement for the Retirement Equity Portfolio will remain in effect through February 28, 2013, and may not be terminated by the Advisor prior to that date.