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Risk/Return: rr_RiskReturnAbstract  
Registrant Name dei_EntityRegistrantName DFA INVESTMENT DIMENSIONS GROUP INC
Prospectus Date rr_ProspectusDate Feb. 28, 2013
CSTG&E U.S. Social Core Equity 2 Portfolio
  
Risk/Return: rr_RiskReturnAbstract  
Risk/Return [Heading] rr_RiskReturnHeading CSTG&E U.S. Social Core Equity 2 Portfolio
Objective [Heading] rr_ObjectiveHeading INVESTMENT OBJECTIVE
Objective, Primary [Text Block] rr_ObjectivePrimaryTextBlock The investment objective of the CSTG&E U.S. Social Core Equity 2 Portfolio (the “U.S. Social Core Portfolio”) is to achieve long-term capital appreciation.
Expense [Heading] rr_ExpenseHeading FEES AND EXPENSES OF THE PORTFOLIO
Expense Narrative [Text Block] rr_ExpenseNarrativeTextBlock This table describes the fees and expenses you may pay if you buy and hold shares of the U.S. Social Core Portfolio.
Shareholder Fees Caption [Text] rr_ShareholderFeesCaption Shareholder Fees (fees paid directly from your investment):
Operating Expenses Caption [Text] 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 [Text Block] rr_PortfolioTurnoverTextBlock The U.S. Social Core Portfolio 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 Portfolio’s performance. During the most recent fiscal year, the U.S. Social Core Portfolio’s portfolio turnover rate was 9% of the average value of its investment portfolio.
Portfolio Turnover, Rate rr_PortfolioTurnoverRate 9.00%
Expense Example [Heading] rr_ExpenseExampleHeading Example
Expense Example Narrative [Text Block] rr_ExpenseExampleNarrativeTextBlock This Example is meant to help you compare the cost of investing in the U.S. Social Core Portfolio with the cost of investing in other mutual funds. The Example assumes that you invest $10,000 in the Portfolio 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 Portfolio’s operating expenses remain the same. Although your actual costs may be higher or lower, based on these assumptions your costs would be:
Strategy [Heading] rr_StrategyHeading PRINCIPAL INVESTMENT STRATEGIES
Strategy Narrative [Text Block] rr_StrategyNarrativeTextBlock Dimensional Fund Advisors LP (the "Advisor") believes that equity investing should involve a long-term view and a systematic focus on sources of expected returns, not on stock picking or market timing. In constructing an investment portfolio, the Advisor identifies a broadly diversified universe of eligible securities with precisely-defined risk and return characteristics. It then places priority on efficiently managing portfolio turnover and keeping trading costs low. In general, the Advisor does not intend to purchase or sell securities for the investment portfolio based on prospects for the economy, the securities markets or the individual issuers whose shares are eligible for purchase.

The U.S. Social Core Portfolio purchases a broad and diverse group of securities of U.S. companies with a greater emphasis on small capitalization and value companies as compared to their representation in the U.S. Universe, while excluding companies based on the Portfolio's social issue screens. The Advisor generally defines the U.S. Universe as a free float adjusted market capitalization weighted portfolio of U.S. operating companies listed on the New York Stock Exchange ("NYSE"), NYSE Alternext US LLC or Nasdaq Global Market® or such other securities exchanges deemed appropriate by the Advisor. The Portfolio's increased exposure to small and value companies may be achieved by decreasing the allocation of the Portfolio's assets to the largest U.S. growth companies relative to their weight in the U.S. Universe. An equity issuer is considered a growth company primarily because it has a low, non-negative book value in relation to its market capitalization. An equity issuer is considered a value company primarily because it has a high book value in relation to its market capitalization.

As a non-fundamental policy, under normal circumstances, U.S. Social Core Portfolio will invest at least 80% of its net assets in equity securities of U.S. companies. The percentage allocation of the assets of the U.S. Social Core Portfolio to securities of the largest U.S. growth companies as defined above will generally be reduced from between 5% and 35% of their percentage weight in the U.S. Universe. For example, as of December 31, 2012, securities of the largest U.S. growth companies comprised 32% of the U.S. Universe and the Advisor allocated approximately 10% of the U.S. Social Core Portfolio to securities of the largest U.S. growth companies. The percentage by which the U.S. Social Core Portfolio's allocation to securities of the largest U.S. growth companies is reduced will change due to market movements, results of social issue screens and other factors. Additionally, the range by which the U.S. Social Core Portfolio's percentage allocation to all securities as compared to the U.S. Universe may be modified after considering other factors the Advisor determines to be appropriate such as free float, momentum, trading-strategies, liquidity management, and expected profitability. In assessing expected profitability, the Advisor may consider different ratios, such as that of earnings or profits from operations relative to book value or assets.

The U.S. Social Core Portfolio also may use derivatives, such as futures contracts and options on futures contracts for U.S. equity securities and indices, to gain market exposure on its uninvested cash pending investment in securities or to maintain liquidity to pay redemptions. The above-referenced investments are not subject to, though they may incorporate, the Portfolio's social criteria.

The U.S. Social Core Portfolio may lend its portfolio securities to generate additional income.

The U.S. Social Core Portfolio seeks to purchase securities that are consistent with the Portfolio's social issue screens, which are monitored by an independent third party. The Portfolio seeks to exclude from its investment portfolio those companies that are identified by the Portfolio's social issue screens. The Portfolio's social issue screens generally are designed to identify companies that derive 15% or more of their revenue from the following industries: Casinos and Gambling; Drug retail; Brewers; Distillers and Vintners; Tobacco; Health Care Equipment and Supplies; Health Care Distributors; Health Care Facilities; Health Care Services; Managed Health Care; Health Care Technology; Biotechnology; Life Sciences Tools and Services; Pharmaceuticals; and Adult Entertainment. The Portfolio may modify this list of social issue screens, at any time, without prior shareholder approval or notice.
Risk [Heading] rr_RiskHeading PRINCIPAL RISKS
Risk Narrative [Text Block] rr_RiskNarrativeTextBlock Market Risk: Even a long-term investment approach cannot guarantee a profit. Economic, political, and issuer-specific events will cause the value of securities, and the U.S. Social Core Portfolio that owns them, to rise or fall. Because the value of your investment in the Portfolio will fluctuate, there is the risk that you will lose money.

Value Investment Risk: Value stocks may perform differently from the market as a whole and following a value-oriented investment strategy may cause the Portfolio to at times underperform equity funds that use other investment strategies.

Small Company Risk: Securities of small companies are often less liquid than those of large companies and this could make it difficult to sell a small company security at a desired time or price. As a result, small company stocks may fluctuate relatively more in price. In general, smaller capitalization companies are also more vulnerable than larger companies to adverse business or economic developments and they may have more limited resources.

Social Investment Risk: The U.S. Social Core Portfolio's social issue screens may limit the number of investment opportunities available to the Portfolio, and as a result, at times the Portfolio may produce different returns than funds that are not subject to such special investment conditions. For example, the Portfolio may decline to purchase certain securities when it is otherwise advantageous to do so, or the Portfolio may sell certain securities for social reasons when it is otherwise disadvantageous to do so.

Derivatives Risk: Derivatives are instruments, such as futures contracts, whose value is derived from that of other assets, rates or indices. The use of derivatives for non-hedging purposes may be considered more speculative than other types of investments. When the U.S. Social Core Portfolio uses derivatives, the Portfolio will be directly exposed to the risks of that derivative. Derivative instruments are subject to a number of risks including liquidity, interest rate, market, credit and management risks, and the risk of improper valuation. Changes in the value of a derivative may not correlate perfectly with the underlying asset, rate or index, and the Portfolio could lose more than the principal amount invested.

Securities Lending Risk: Securities lending involves the risk that the borrower may fail to return the securities in a timely manner or at all. As a result, the U.S. Social Core Portfolio may lose money and there may be a delay in recovering the loaned securities. The U.S. Social Core Portfolio could also lose money if it does not recover the securities and/or the value of the collateral falls, including the value of investments made with cash collateral. Securities lending also may have certain adverse tax consequences.
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
Performance Narrative [Text Block] rr_PerformanceNarrativeTextBlock The bar chart and table immediately following illustrate the variability of the U.S. Social Core 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 U.S. Social Core Portfolio’s performance from year to year. The table illustrates how annualized one year, five year and since inception returns, both before and after taxes, compare with those of a broad measure of market performance. The U.S. Social Core Portfolio’s past performance (before and after taxes) is not an indication of future results. Updated performance information for the Portfolio can be obtained by visiting www.dimensional.com.

The after-tax returns presented in the table for the U.S. Social Core Portfolio are calculated using the historical highest individual federal marginal income tax rates and do not reflect the impact of state and local taxes. Actual after-tax returns depend on an investor’s tax situation and may differ from those shown in the table. 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. A negative pre-tax total return translates into a higher after-tax return because this calculation assumes that an investor received a tax deduction for the loss incurred on the sale.
Performance Information Illustrates Variability of Returns [Text] rr_PerformanceInformationIllustratesVariabilityOfReturns The bar chart and table immediately following illustrate the variability of the U.S. Social Core 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 U.S. Social Core 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 U.S. Social Core Portfolio’s past performance (before and after taxes) is not an indication of future results.
Bar Chart [Heading] rr_BarChartHeading CSTG&E U.S. Social Core Equity 2 Portfolio
Total returns (%)
Bar Chart Closing [Text Block] rr_BarChartClosingTextBlock January 2008-December 2012

Highest Quarter    Lowest Quarter
19.58 (4/09-6/09)    -25.41 (10/08-12/08)
Performance Table Heading rr_PerformanceTableHeading Periods ending December 31, 2012
Annualized Returns (%)
Performance Table Uses Highest Federal Rate rr_PerformanceTableUsesHighestFederalRate The after-tax returns presented in the table for the U.S. Social Core 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.
Performance Table Explanation after Tax Higher rr_PerformanceTableExplanationAfterTaxHigher A negative pre-tax total return translates into a higher after-tax return because this calculation assumes that an investor received a tax deduction for the loss incurred on the sale.
CSTG&E U.S. Social Core Equity 2 Portfolio | CSTG&E U.S. Social Core Equity 2 Portfolio Shares
  
Risk/Return: rr_RiskReturnAbstract  
Shareholder Fees (fees paid directly from your investment) rr_ShareholderFeeOther none
Management Fee rr_ManagementFeesOverAssets 0.27%
Other Expenses rr_OtherExpensesOverAssets 0.09%
Total Annual Fund Operating Expenses rr_ExpensesOverAssets 0.36%
1 Year rr_ExpenseExampleYear01 37
3 Years rr_ExpenseExampleYear03 116
5 Years rr_ExpenseExampleYear05 202
10 Years rr_ExpenseExampleYear10 456
2008 rr_AnnualReturn2008 (38.23%)
2009 rr_AnnualReturn2009 29.66%
2010 rr_AnnualReturn2010 23.26%
2011 rr_AnnualReturn2011 (2.33%)
2012 rr_AnnualReturn2012 17.13%
Highest Quarterly Return, Label rr_HighestQuarterlyReturnLabel Highest Quarter
Highest Quarterly Return, Date rr_BarChartHighestQuarterlyReturnDate Jun. 30, 2009
Highest Quarterly Return rr_BarChartHighestQuarterlyReturn 19.58%
Lowest Quarterly Return, Label rr_LowestQuarterlyReturnLabel Lowest Quarter
Lowest Quarterly Return, Date rr_BarChartLowestQuarterlyReturnDate Dec. 31, 2008
Lowest Quarterly Return rr_BarChartLowestQuarterlyReturn (25.41%)
One Year rr_AverageAnnualReturnYear01 17.13%
Five Year rr_AverageAnnualReturnYear05 2.46%
Since Inception rr_AverageAnnualReturnSinceInception 2.22%
Inception Date rr_AverageAnnualReturnInceptionDate Aug. 03, 2007
CSTG&E U.S. Social Core Equity 2 Portfolio | Return After Taxes on Distributions | CSTG&E U.S. Social Core Equity 2 Portfolio Shares
  
Risk/Return: rr_RiskReturnAbstract  
One Year rr_AverageAnnualReturnYear01 16.80%
Five Year rr_AverageAnnualReturnYear05 2.19%
Since Inception rr_AverageAnnualReturnSinceInception 1.95%
Inception Date rr_AverageAnnualReturnInceptionDate Aug. 03, 2007
CSTG&E U.S. Social Core Equity 2 Portfolio | Return After Taxes on Distributions and Sale of Portfolio Shares | CSTG&E U.S. Social Core Equity 2 Portfolio Shares
  
Risk/Return: rr_RiskReturnAbstract  
One Year rr_AverageAnnualReturnYear01 11.54%
Five Year rr_AverageAnnualReturnYear05 2.04%
Since Inception rr_AverageAnnualReturnSinceInception 1.83%
Inception Date rr_AverageAnnualReturnInceptionDate Aug. 03, 2007
CSTG&E U.S. Social Core Equity 2 Portfolio | Russell 3000® Index (reflects no deduction for fees, expenses, or taxes)
  
Risk/Return: rr_RiskReturnAbstract  
One Year rr_AverageAnnualReturnYear01 16.42%
Five Year rr_AverageAnnualReturnYear05 2.04%
Since Inception rr_AverageAnnualReturnSinceInception 2.50%