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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
R Shares | EMERGING MARKETS VALUE PORTFOLIO | Class R2
 
Risk/Return: rr_RiskReturnAbstract  
Shareholder Fees (fees paid directly from your investment) rr_MaximumAccountFee none
Management Fee rr_ManagementFeesOverAssets 0.50% [1]
Shareholder Services Fees rr_Component1OtherExpensesOverAssets 0.25% [1],[2]
Other Expenses rr_Component3OtherExpensesOverAssets 0.11% [1]
Total Other Expenses rr_OtherExpensesOverAssets 0.36% [1]
Total Annual Fund Operating Expenses rr_ExpensesOverAssets 0.86% [1]
1 Year rr_ExpenseExampleYear01 88
3 Years rr_ExpenseExampleYear03 274
5 Years rr_ExpenseExampleYear05 477
10 Years rr_ExpenseExampleYear10 1,061
Annual Return 2009 rr_AnnualReturn2009 92.31%
Annual Return 2010 rr_AnnualReturn2010 21.46%
Annual Return 2011 rr_AnnualReturn2011 (25.80%)
Highest Quarterly Return, Label rr_HighestQuarterlyReturnLabel Highest Quarter
Highest Quarterly Return, Date rr_BarChartHighestQuarterlyReturnDate Jun. 30, 2009
Highest Quarterly Return rr_BarChartHighestQuarterlyReturn 44.77%
Lowest Quarterly Return, Label rr_LowestQuarterlyReturnLabel Lowest Quarter
Lowest Quarterly Return, Date rr_BarChartLowestQuarterlyReturnDate Sep. 30, 2011
Lowest Quarterly Return rr_BarChartLowestQuarterlyReturn (26.93%)
One Year rr_AverageAnnualReturnYear01 (25.80%)
Since Inception rr_AverageAnnualReturnSinceInception (2.99%)
Inception Date rr_AverageAnnualReturnInceptionDate Jan. 29, 2008
R Shares | EMERGING MARKETS VALUE 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
Portfolio Turnover [Heading] rr_PortfolioTurnoverHeading
Portfolio Turnover [Text Block] rr_PortfolioTurnoverTextBlock
The Emerging Markets Value Fund pays transaction costs, such as commissions, when it buys and sells securities (or "turns over" its portfolio). A higher portfolio turnover may indicate higher transaction costs and may result in higher taxes when Portfolio shares are held in a taxable account. These costs, which are not reflected in Annual Fund Operating Expenses or in the Example, affect the Emerging Markets Value Portfolio's performance. During the most recent fiscal year, the Emerging Markets Value Fund's portfolio turnover rate was 5% of the average value of its investment portfolio.
Portfolio Turnover, Rate rr_PortfolioTurnoverRate 5.00%
Expense Example [Heading] rr_ExpenseExampleHeading
Expense Example Narrative [Text Block] rr_ExpenseExampleNarrativeTextBlock
Expense Example Closing [Text Block] rr_ExpenseExampleClosingTextBlock
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.
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 Emerging Markets Value 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 performance of the Portfolio's Class R2 shares from year to year.
Performance Availability Website Address [Text] rr_PerformanceAvailabilityWebSiteAddress www.dimensional.com
Performance Past Does Not Indicate Future [Text] rr_PerformancePastDoesNotIndicateFuture The Emerging Markets Value Portfolio's past performance is not an indication of future results.
Bar Chart [Heading] rr_BarChartHeading
Bar Chart Closing [Text Block] rr_BarChartClosingTextBlock
Performance Table Heading rr_PerformanceTableHeading
R Shares | EMERGING MARKETS VALUE PORTFOLIO | MSCI Emerging Markets Index (net dividends) (reflects no deduction for fees, expenses, or taxes on sales)
 
Risk/Return: rr_RiskReturnAbstract  
One Year rr_AverageAnnualReturnYear01 (18.42%)
Since Inception rr_AverageAnnualReturnSinceInception (2.35%)
[1] The "Management Fee" includes an investment management fee payable by the Emerging Markets Value Fund and an administration fee payable by the Emerging Markets Value Portfolio. The amounts set forth above reflect the direct expenses of the Emerging Markets Value Portfolio and the indirect expenses of the Portfolio's portion of the expenses of the Emerging Markets Value Fund.
[2] An amount up to 0.25% of the average net assets of the Portfolio's Class R2 shares may be used to compensate service agents that provide shareholder servicing, record keeping, account maintenance and other services to investors in the Portfolio's Class R2 shares ("Shareholder Services Agent").