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Risk/Return: rr_RiskReturnAbstract  
Registrant Name dei_EntityRegistrantName DFA INVESTMENT DIMENSIONS GROUP INC
Prospectus Date rr_ProspectusDate Feb. 28, 2013
Institutional Shares | International Sustainability Core 1 Portfolio
  
Risk/Return: rr_RiskReturnAbstract  
Risk/Return [Heading] rr_RiskReturnHeading International Sustainability Core 1 Portfolio
Objective [Heading] rr_ObjectiveHeading INVESTMENT OBJECTIVE
Objective, Primary [Text Block] rr_ObjectivePrimaryTextBlock The investment objective of the International Sustainability Core 1 Portfolio is 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 International Sustainability Core 1 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)
Fee Waiver or Reimbursement over Assets, Date of Termination rr_FeeWaiverOrReimbursementOverAssetsDateOfTermination February 28, 2014
Portfolio Turnover [Heading] rr_PortfolioTurnoverHeading Portfolio Turnover
Portfolio Turnover [Text Block] rr_PortfolioTurnoverTextBlock The International Sustainability Core 1 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 International Sustainability Core 1 Portfolio’s performance. During the most recent fiscal year, the International Sustainability Core 1 Portfolio’s portfolio turnover rate was 11% of the average value of its investment portfolio.
Portfolio Turnover, Rate rr_PortfolioTurnoverRate 11.00%
Expense Example [Heading] rr_ExpenseExampleHeading Example
Expense Example by Year [Heading] rr_ExpenseExampleByYearHeading This Example is meant to help you compare the cost of investing in the International Sustainability Core 1 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. The costs for the Portfolio reflect the net expenses of the Portfolio that result from the contractual expense waiver and assumption in the first year only. 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 International Sustainability Core 1 Portfolio purchases a broad and diverse group of securities of non-U.S. companies in developed markets with a greater emphasis on small capitalization and value companies as compared to their representation in the International Universe, while adjusting the composition of the Portfolio based on environmental impact considerations. For purposes of this Portfolio, the Advisor defines the International Universe as a market capitalization weighted portfolio of non-U.S. companies in developed markets that have been authorized as approved markets for investment by the Advisor's Investment Committee. The Portfolio's increased exposure to small capitalization and value companies may be achieved by decreasing the allocation of the International Sustainability Core 1 Portfolio's assets to the largest growth companies relative to their weight in the International Universe, which would result in a greater weight allocation to small capitalization and value companies. 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.

The International Sustainability Core 1 Portfolio intends to purchase securities of companies associated with developed market countries that the Advisor has designated as approved markets. As a non-fundamental policy, under normal circumstances, the International Sustainability Core 1 Portfolio will invest at least 80% of its net assets in equity securities. The Advisor determines company size on a country or region specific basis and based primarily on market capitalization. The percentage allocation of the assets of the International Sustainability Core 1 Portfolio to securities of the largest growth companies as defined above will generally be reduced from between 5% and 35% of their percentage weight in the International Universe. As of December 31, 2012, securities of the largest growth companies in the International Universe comprised approximately 16% of the International Universe and the Advisor allocated approximately 9% of the International Sustainability Core 1 Portfolio to securities of the largest growth companies in the International Universe. The percentage by which the Portfolio's allocation to securities of the largest growth companies is reduced will change due to market movements, environmental impact considerations and other factors. Additionally, the range by which the Portfolio's percentage allocation to all securities as compared to the International Universe may be impacted by the Portfolio's investment strategies with respect to environmental impact considerations and 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 International Sustainability Core 1 Portfolio may gain exposure to companies associated with approved markets by purchasing equity securities in the form of depositary receipts, which may be listed or traded outside the issuer's domicile country. The International Sustainability Core 1 Portfolio also may use derivatives, such as futures contracts and options on futures contracts for foreign or 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, although they may incorporate, the International Sustainability Core 1 Portfolio's environmental impact considerations.

The International Sustainability Core 1 Portfolio may lend its portfolio securities to generate additional income.

The Advisor intends to take into account the impact that companies have on the environment when making investment decisions for the International Sustainability Core 1 Portfolio by adjusting the composition of the Portfolio based on environmental impact considerations. Relative to a portfolio without environmental impact considerations, the International Sustainability Core 1 Portfolio intends to exclude or underweight securities of companies that, according to the Portfolio's environmental impact considerations, may have a relatively negative impact on the environment as compared either to other companies in the Portfolio's entire investment universe or other companies with similar business lines. Similarly, relative to a portfolio without environmental impact considerations, the International Sustainability Core 1 Portfolio intends to overweight securities of companies that, according to the Portfolio's environmental impact considerations, may have a relatively positive impact on the environment as compared either to other companies in the Portfolio's entire investment universe or other companies with similar business lines. Negative factors include issues relating to agricultural chemicals, climate change, hazardous waste, ozone depleting chemicals, regulatory problems, substantial emissions, negative economic impact, and other environmental concerns. Positive factors include issues relating to beneficial products and services, clean energy, environmental management systems, pollution prevention, recycling and other strengths. The Advisor has engaged a third party service provider to provide research and ratings information relating to the International Sustainability Core 1 Portfolio's environmental impact considerations with respect to securities in the portfolio, where information is available from such provider.
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 International Sustainability Core 1 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.

Foreign Securities and Currencies Risk: Foreign securities prices may decline or fluctuate because of: (a) economic or political actions of foreign governments, and/or (b) less regulated or liquid securities markets. Investors holding these securities may also be exposed to foreign currency risk (the possibility that foreign currency will fluctuate in value against the U.S. dollar or that a foreign government will convert, or be forced to convert, its currency to another currency, changing its value against the U.S. dollar). The International Sustainability Core 1 Portfolio does not hedge foreign currency risk.

Environmental Impact Consideration Investment Risk: The International Sustainability Core 1 Portfolio's environmental impact considerations may limit the number of investment opportunities available to the Portfolio, and as a result, at times, the Portfolio may produce different results than funds that are not subject to such special investment considerations. For example, the Portfolio may decline to purchase, or underweight its investment in, certain securities due to environmental impact considerations when other investment considerations would suggest that a more significant investment in such securities would be advantageous. In addition, the Portfolio may sell certain securities due to environmental impact considerations when it is otherwise disadvantageous to do so. The environmental impact considerations may cause the Portfolio's industry allocation to deviate from that of funds without these considerations and of conventional benchmarks.

Derivatives Risk: Derivatives are instruments, such as futures and foreign exchange forward 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 International Sustainability Core 1 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 International Sustainability Core 1 Portfolio may lose money and there may be a delay in recovering the loaned securities. The International Sustainability Core 1 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 International Sustainability Core 1 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 International Sustainability Core 1 Portfolio’s performance from year to year. The table illustrates how annualized one year and since inception returns, both before and after taxes, compare with those of a broad measure of market performance. The International Sustainability Core 1 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 International Sustainability Core 1 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 International Sustainability Core 1 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 International Sustainability Core 1 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 International Sustainability Core 1 Portfolio’s past performance (before and after taxes) is not an indication of future results.
Bar Chart [Heading] rr_BarChartHeading International Sustainability Core 1 Portfolio
Total Returns (%)
Bar Chart Closing [Text Block] rr_BarChartClosingTextBlock January 2009-December 2012

Highest Quarter    Lowest Quarter
28.71 (4/09-6/09)    -20.91 (7/11-9/11)
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 International Sustainability Core 1 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.
Institutional Shares | International Sustainability Core 1 Portfolio | International Sustainability Core 1 Portfolio Shares
  
Risk/Return: rr_RiskReturnAbstract  
Shareholder Fees (fees paid directly from your investment) rr_ShareholderFeeOther none
Management Fee rr_ManagementFeesOverAssets 0.42%
Other Expenses rr_OtherExpensesOverAssets 0.14%
Total Annual Fund Operating Expenses rr_ExpensesOverAssets 0.56%
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 0.57%
1 Year rr_ExpenseExampleYear01 58
3 Years rr_ExpenseExampleYear03 180
5 Years rr_ExpenseExampleYear05 314
10 Years rr_ExpenseExampleYear10 702
2009 rr_AnnualReturn2009 34.95%
2010 rr_AnnualReturn2010 11.54%
2011 rr_AnnualReturn2011 (14.04%)
2012 rr_AnnualReturn2012 18.10%
Highest Quarterly Return, Label rr_HighestQuarterlyReturnLabel Highest Quarter
Highest Quarterly Return, Date rr_BarChartHighestQuarterlyReturnDate Jun. 30, 2009
Highest Quarterly Return rr_BarChartHighestQuarterlyReturn 28.71%
Lowest Quarterly Return, Label rr_LowestQuarterlyReturnLabel Lowest Quarter
Lowest Quarterly Return, Date rr_BarChartLowestQuarterlyReturnDate Sep. 30, 2011
Lowest Quarterly Return rr_BarChartLowestQuarterlyReturn (20.91%)
One Year rr_AverageAnnualReturnYear01 18.10%
Since Inception rr_AverageAnnualReturnSinceInception (1.18%)
Inception Date rr_AverageAnnualReturnInceptionDate Mar. 12, 2008
Institutional Shares | International Sustainability Core 1 Portfolio | Return After Taxes on Distributions | International Sustainability Core 1 Portfolio Shares
  
Risk/Return: rr_RiskReturnAbstract  
One Year rr_AverageAnnualReturnYear01 17.58%
Since Inception rr_AverageAnnualReturnSinceInception (1.53%)
Inception Date rr_AverageAnnualReturnInceptionDate Mar. 12, 2008
Institutional Shares | International Sustainability Core 1 Portfolio | Return After Taxes on Distributions and Sale of Portfolio Shares | International Sustainability Core 1 Portfolio Shares
  
Risk/Return: rr_RiskReturnAbstract  
One Year rr_AverageAnnualReturnYear01 12.28%
Since Inception rr_AverageAnnualReturnSinceInception (1.01%)
Inception Date rr_AverageAnnualReturnInceptionDate Mar. 12, 2008
Institutional Shares | International Sustainability Core 1 Portfolio | MSCI World ex USA Index (net dividends) (reflects no deduction for fees, expenses, or taxes on sales)
  
Risk/Return: rr_RiskReturnAbstract  
One Year rr_AverageAnnualReturnYear01 16.41%
Since Inception rr_AverageAnnualReturnSinceInception (1.69%)
[1] The Advisor has agreed to waive certain fees and in certain instances, assume certain expenses of the International Sustainability Core 1 Portfolio. The Amended and Restated Fee Waiver and/or Expense Assumption Agreement for the International Sustainability Core 1 Portfolio will remain in effect through February 28, 2014, 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.