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Risk/Return: rr_RiskReturnAbstract  
Registrant Name dei_EntityRegistrantName DFA INVESTMENT DIMENSIONS GROUP INC
Prospectus Date rr_ProspectusDate Feb. 28, 2016
International Social Core Equity Portfolio  
Risk/Return: rr_RiskReturnAbstract  
Risk/Return [Heading] rr_RiskReturnHeading International Social Core Equity Portfolio
Objective [Heading] rr_ObjectiveHeading Investment Objective
Objective, Primary [Text Block] rr_ObjectivePrimaryTextBlock The investment objective of the International Social Core Equity 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 International Social Core Equity 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 International Social Core Equity 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 mutual fund 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 International Social Core Equity Portfolio’s portfolio turnover rate was 7% of the average value of its investment portfolio.
Portfolio Turnover, Rate rr_PortfolioTurnoverRate 7.00%
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 International Social Core Equity 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 The International Social Core Equity 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 excluding securities of certain companies based on the Portfolio’s social issue screens. For the purposes of this Portfolio, Dimensional Fund Advisors LP (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 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. Securities are considered to be value stocks primarily because a company’s shares have a high book value in relation to their market value.

The International Social Core Equity 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 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 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, 2015, securities of the largest growth companies in the International Universe comprised approximately 14% of the International Universe and the Advisor allocated approximately 3% of the International Social Core Equity 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. The Advisor may also adjust the representation in the International Social Core Equity Portfolio of an eligible company, or exclude a company, after considering such factors as free float, momentum, trading strategies, liquidity management, profitability, and other factors that the Advisor determines to be appropriate, given market conditions. In assessing profitability, the Advisor may consider different ratios, such as that of earnings or profits from operations relative to book value or assets.

The International Social Core Equity 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 Portfolio may use derivatives, such as futures contracts and options on futures contracts for approved market or other equity market securities and indices, including those of the United States, to adjust market exposure based on actual or expected cash inflows to or outflows from the Portfolio. The Portfolio does not intend to use derivatives for purposes of speculation or leveraging investment returns. The above-referenced investments are not subject to, although they may incorporate, the Portfolio’s social criteria.

The International Social Core Equity Portfolio may lend its portfolio securities to generate additional income.

The International Social Core Equity Portfolio seeks to purchase securities that are consistent with the Portfolio’s social issue screens, which are monitored by an independent third party. The International Social Core Equity Portfolio seeks to exclude from its investment portfolio those companies that are identified by the Portfolio’s social issue screens, as further discussed below. The Portfolio’s social issue screens are designed to identify companies that: (1) earn at least 20% of their total annual revenue through the production and/or sale of conventional or nuclear weapons, their weapon systems, or critical components of these products, or the provision of weapon systems support and service; (2) are engaged in certain for profit business activities in or with the Republic of the Sudan; (3) earn at least 15% of their total annual revenue through the production and/or sale of tobacco or alcohol products, or key products or raw materials necessary for their production; (4) earn at least 20% of their total annual revenue from certain gambling activities, the production of goods used exclusively for gambling, or the provision of certain services in casinos that are fundamental to gambling operations; (5) directly participate in abortions, or develop or manufacture abortive agents or contraceptives; (6) earn at least 15% of their total annual revenue from the rental, sale, distribution or production of pornographic materials, or the ownership or operation of adult entertainment establishments; (7) have had major recent controversies relating to child labor infractions in the U.S. or abroad; (8) are involved in the production or manufacture of landmines, cluster munitions, or the essential components of these products; and/or (9) are involved in stem cell research.

The International Social Core Equity 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 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.

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 Portfolio does not hedge foreign currency risk.

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 International Social Core Equity 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 swaps, 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 Social Core Equity 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 counterparty, 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 Social Core Equity Portfolio may lose money and there may be a delay in recovering the loaned securities. The International Social Core Equity 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.

Cyber Security Risk: The International Social Core Equity Portfolio’s and its service providers’ use of internet, technology and information systems may expose the Portfolio to potential risks linked to cyber security breaches of those technological or information systems. Cyber security breaches, amongst other things, could allow an unauthorized party to gain access to proprietary information, customer data, or fund assets, or cause the Portfolio and/or its service providers to suffer data corruption or lose operational functionality.
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 Social Core Equity 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 Social Core Equity 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 Social Core Equity 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 http://us.dimensional.com.

The after-tax returns presented in the table for the International Social Core Equity 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.
Performance Information Illustrates Variability of Returns [Text] rr_PerformanceInformationIllustratesVariabilityOfReturns The bar chart and table immediately following illustrate the variability of the International Social Core Equity 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 Social Core Equity Portfolio’s performance from year to year.
Performance Availability Website Address [Text] rr_PerformanceAvailabilityWebSiteAddress http://us.dimensional.com
Performance Past Does Not Indicate Future [Text] rr_PerformancePastDoesNotIndicateFuture The International Social Core Equity Portfolio’s past performance (before and after taxes) is not an indication of future results.
Bar Chart [Heading] rr_BarChartHeading International Social Core Equity Portfolio—Total Returns
Bar Chart Closing [Text Block] rr_BarChartClosingTextBlock January 2013-December 2015

Highest Quarter    Lowest Quarter
12.98% (7/13–9/13)    -10.29% (7/15–9/15)
Performance Table Heading rr_PerformanceTableHeading Annualized Returns (%)
Periods ending December 31, 2015
Performance Table Uses Highest Federal Rate rr_PerformanceTableUsesHighestFederalRate The after-tax returns presented in the table for the International Social Core Equity 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.
International Social Core Equity Portfolio | Institutional Class  
Risk/Return: rr_RiskReturnAbstract  
Shareholder Fees (fees paid directly from your investment) rr_ShareholderFeeOther none
Management Fee rr_ManagementFeesOverAssets 0.37%
Other Expenses rr_OtherExpensesOverAssets 0.09%
Total Annual Fund Operating Expenses rr_ExpensesOverAssets 0.46%
1 YEAR rr_ExpenseExampleYear01 $ 47
3 YEARS rr_ExpenseExampleYear03 148
5 YEARS rr_ExpenseExampleYear05 258
10 YEARS rr_ExpenseExampleYear10 $ 579
2013 rr_AnnualReturn2013 22.35%
2014 rr_AnnualReturn2014 (7.03%)
2015 rr_AnnualReturn2015 (0.75%)
Highest Quarterly Return, Label rr_HighestQuarterlyReturnLabel Highest Quarter
Highest Quarterly Return, Date rr_BarChartHighestQuarterlyReturnDate Sep. 30, 2013
Highest Quarterly Return rr_BarChartHighestQuarterlyReturn 12.98%
Lowest Quarterly Return, Label rr_LowestQuarterlyReturnLabel Lowest Quarter
Lowest Quarterly Return, Date rr_BarChartLowestQuarterlyReturnDate Sep. 30, 2015
Lowest Quarterly Return rr_BarChartLowestQuarterlyReturn (10.29%)
1 YEAR rr_AverageAnnualReturnYear01 (0.75%)
SINCE INCEPTION rr_AverageAnnualReturnSinceInception 5.63%
INCEPTION DATE rr_AverageAnnualReturnInceptionDate Nov. 01, 2012
International Social Core Equity Portfolio | Return After Taxes on Distributions | Institutional Class  
Risk/Return: rr_RiskReturnAbstract  
1 YEAR rr_AverageAnnualReturnYear01 (1.33%)
SINCE INCEPTION rr_AverageAnnualReturnSinceInception 4.90%
INCEPTION DATE rr_AverageAnnualReturnInceptionDate Nov. 01, 2012
International Social Core Equity Portfolio | Return After Taxes on Distributions and Sale of Portfolio Shares | Institutional Class  
Risk/Return: rr_RiskReturnAbstract  
1 YEAR rr_AverageAnnualReturnYear01 0.07%
SINCE INCEPTION rr_AverageAnnualReturnSinceInception 4.33%
INCEPTION DATE rr_AverageAnnualReturnInceptionDate Nov. 01, 2012
International Social Core Equity Portfolio | MSCI World ex USA Index (reflects no deduction for fees, expenses, or taxes on sales)  
Risk/Return: rr_RiskReturnAbstract  
1 YEAR rr_AverageAnnualReturnYear01 (3.04%)
SINCE INCEPTION rr_AverageAnnualReturnSinceInception 5.19%