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Risk/Return: rr_RiskReturnAbstract  
Registrant Name dei_EntityRegistrantName DFA INVESTMENT DIMENSIONS GROUP INC
Prospectus Date rr_ProspectusDate Feb. 28, 2013
DFA Selectively Hedged Global Fixed Income Portfolio
  
Risk/Return: rr_RiskReturnAbstract  
Risk/Return [Heading] rr_RiskReturnHeading DFA Selectively Hedged Global Fixed Income Portfolio
Objective [Heading] rr_ObjectiveHeading INVESTMENT OBJECTIVE
Objective, Primary [Text Block] rr_ObjectivePrimaryTextBlock The investment objective of the DFA Selectively Hedged Global Fixed Income Portfolio (the “Selectively Hedged Global Portfolio”) is to maximize total returns within the universe of domestic and foreign debt securities that the Portfolio invests. Total return is comprised of income and 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 Selectively Hedged Global 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 Selectively Hedged Global 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 Portfolio’s portfolio turnover rate was 109% of the average value of its investment portfolio.
Portfolio Turnover, Rate rr_PortfolioTurnoverRate 109.00%
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 Selectively Hedged Global 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 fixed income investing should involve a long-term view and a systematic focus on bond market risk and return, not on interest rate forecasting or market timing.

In constructing an investment portfolio, the Advisor identifies a broadly diversified universe of eligible securities with precisely defined maturity ranges and credit quality characteristics. The Advisor will then seek to purchase a broad and diverse portfolio of securities meeting these credit quality standards. In making these purchase decisions, if the anticipated maturity risk premium is greater for longer-term securities in the eligible maturity range, the Advisor will focus investment in that longer-term area, otherwise, the portfolio will focus investment in the short-term range of the eligible maturity range. The Advisor also places priority on efficiently managing portfolio turnover and keeping trading costs low.

The Selectively Hedged Global Portfolio seeks to maximize total returns from a universe of U.S. and foreign debt securities maturing in five years or less from the date of settlement. The Portfolio may selectively hedge its currency exposures depending on market conditions. The debt securities in which the Portfolio may invest include obligations issued or guaranteed by the U.S. and foreign governments, their agencies and instrumentalities, corporate debt obligations, bank obligations, commercial paper, repurchase agreements, obligations of other domestic and foreign issuers, securities of domestic or foreign issuers denominated in U.S. dollars but not trading in the United States, and obligations of supranational organizations. At the present time, the Advisor expects that most investments will be made in the obligations of issuers that are located in developed countries. However, in the future, the Advisor anticipates investing in issuers located in other countries as well. The fixed income securities in which the Selectively Hedged Global Portfolio invests are considered investment grade at the time of purchase. Under normal market conditions, the Portfolio intends to invest its assets in issuers organized or having a majority of their assets in, or deriving a majority of their operating income in, at least three different countries, one of which may be the United States.

As a non-fundamental policy, under normal circumstances, the Portfolio will invest at least 80% of its net assets in fixed income securities. The Selectively Hedged Global Portfolio primarily invests in securities that mature within five years from the date of settlement and maintains an average portfolio maturity and an average portfolio duration of three years or less. Duration is a measure of the expected life of a fixed income security that is used to determine the sensitivity of a security's price to changes in interest rates. The longer a security's duration, the more sensitive it will be to changes in interest rates.

Because many of the Selectively Hedged Global Portfolio's investments may be denominated in foreign currencies, the Portfolio may hedge the currency exposure of the foreign securities by entering into foreign forward currency contracts, or leave some or all of the currency exposure unhedged, to attempt to protect against uncertainty in the level of future foreign currency rates, to hedge against fluctuations in currency exchange rates or to transfer balances from one currency to another. The decision to hedge the Portfolio's currency exposure with respect to a foreign market will be based on, among other things, a comparison of the respective foreign and U.S. short-term interest rates and the Portfolio's existing exposure to a given foreign currency. The Portfolio may also enter into foreign forward currency contracts in order to gain exposure to foreign currencies in a more efficient manner. In addition, the Portfolio may use derivatives, such as futures contracts and options on futures contracts, to gain market exposure on its uninvested cash pending investment in securities or to maintain liquidity to pay redemptions.

The Selectively Hedged Global Portfolio may concentrate its investments in obligations of U.S. and foreign banks and bank holding companies. The Portfolio will concentrate its assets (invest more than 25% of its total assets) in obligations of U.S. and/or foreign banks and bank holding companies ("banking industry securities") when the yield to maturity on eligible portfolio investments in banking industry securities as a group generally exceeds the yield to maturity on all other eligible portfolio investments as a group generally for a period of five consecutive days when the New York Stock Exchange is open for trading. See the section entitled "Investments in the Banking Industry" in the Portfolio's prospectus for additional information.
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 Selectively Hedged Global 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.

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 Selectively Hedged Global Portfolio may hedge the currency exposure of its foreign securities or leave some or all of the currency exposed unhedged.

Foreign Government Debt Risk: The risk that: (a) the governmental entity that controls the repayment of government debt may not be willing or able to repay the principal and/or to pay the interest when it becomes due, due to factors such as political considerations, the relative size of the governmental entity's debt position in relation to the economy, cash flow problems, insufficient foreign currency reserves, the failure to put in place economic reforms required by the International Monetary Fund or other multilateral agencies, and/or other national economic factors; (b) governments may default on their debt securities, which may require holders of such securities to participate in debt rescheduling; and (c) there is no legal or bankruptcy process by which defaulted government debt may be collected in whole or in part.

Interest Rate Risk: Fixed income securities are subject to interest rate risk because the prices of fixed income securities tend to move in the opposite direction of interest rates. When interest rates rise, fixed income security prices fall. When interest rates fall, fixed income security prices rise. In general, fixed income securities with longer maturities are more sensitive to these price changes.

Credit Risk: Credit risk is the risk that the issuer of a security may be unable to make interest payments and/or repay principal when due. A downgrade to an issuer's credit rating or a perceived change in an issuer's financial strength may affect a security's value, and thus, impact the Selectively Hedged Global Portfolio's performance. Government agency obligations have different levels of credit support and, therefore, different degrees of credit risk. Securities issued by agencies and instrumentalities of the U.S. Government that are supported by the full faith and credit of the United States, such as the Federal Housing Administration and Ginnie Mae, present little credit risk. Other securities issued by agencies and instrumentalities sponsored by the U.S. Government, that are supported only by the issuer's right to borrow from the U.S. Treasury, subject to certain limitations, and securities issued by agencies and instrumentalities sponsored by the U.S. Government that are sponsored by the credit of the issuing agencies, such as Freddie Mac and Fannie Mae, are subject to a greater degree of credit risk. U.S. government agency securities issued or guaranteed by the credit of the agency may still involve a risk of non-payment of principal and/or interest.

Risks of Banking Concentration: Focus on the banking industry would link the performance of the Selectively Hedged Global Portfolio to changes in the performance of the banking industry generally. Banks are very sensitive to changes in money market and general economic conditions. The profitability of the banking industry is dependent upon banks being able to obtain funds at reasonable costs and upon liquidity in the capital and credit markets to finance their lending operations. Adverse general economic conditions can cause financial difficulties for a bank's borrowers and the borrowers' failure to repay their loans can adversely affect the bank's financial situation. Banks are subject to extensive regulation and decisions by regulators may limit the loans banks make and the interest rates and fees they charge, which could reduce bank profitability.

Income Risk: Income risk is the risk that falling interest rates will cause the Selectively Hedged Global Portfolio's income to decline.

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. Derivatives can be used for hedging (attempting to reduce risk by offsetting one investment position with another) or non-hedging purposes. Hedging with derivatives may increase expenses, and there is no guarantee that a hedging strategy will work. While hedging can reduce or eliminate losses, it can also reduce or eliminate gains. The use of derivatives for non-hedging purposes may be considered more speculative than other types of investments. When the Selectively Hedged Global 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.
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 Selectively Hedged Global 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 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 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 Selectively Hedged Global 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 Selectively Hedged Global 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 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 Portfolio’s past performance (before and after taxes) is not an indication of future results.
Bar Chart [Heading] rr_BarChartHeading DFA Selectively Hedged Global Fixed Income Portfolio Institutional Class Shares
Total Returns (%)
Bar Chart Closing [Text Block] rr_BarChartClosingTextBlock January 2009-December 2012

Highest Quarter    Lowest Quarter
5.62 (4/09-6/09)    -3.63 (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 Selectively Hedged Global 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.
DFA Selectively Hedged Global Fixed Income Portfolio | Institutional Class
  
Risk/Return: rr_RiskReturnAbstract  
Shareholder Fees (fees paid directly from your investment) rr_ShareholderFeeOther none
Management Fee rr_ManagementFeesOverAssets 0.15%
Other Expenses rr_OtherExpensesOverAssets 0.04%
Total Annual Fund Operating Expenses rr_ExpensesOverAssets 0.19%
1 Year rr_ExpenseExampleYear01 19
3 Years rr_ExpenseExampleYear03 61
5 Years rr_ExpenseExampleYear05 107
10 Years rr_ExpenseExampleYear10 243
2009 rr_AnnualReturn2009 10.21%
2010 rr_AnnualReturn2010 4.76%
2011 rr_AnnualReturn2011 0.85%
2012 rr_AnnualReturn2012 4.22%
Highest Quarterly Return, Label rr_HighestQuarterlyReturnLabel Highest Quarter
Highest Quarterly Return, Date rr_BarChartHighestQuarterlyReturnDate Jun. 30, 2009
Highest Quarterly Return rr_BarChartHighestQuarterlyReturn 5.62%
Lowest Quarterly Return, Label rr_LowestQuarterlyReturnLabel Lowest Quarter
Lowest Quarterly Return, Date rr_BarChartLowestQuarterlyReturnDate Sep. 30, 2011
Lowest Quarterly Return rr_BarChartLowestQuarterlyReturn (3.63%)
One Year rr_AverageAnnualReturnYear01 4.22%
Since Inception rr_AverageAnnualReturnSinceInception 2.04%
Inception Date rr_AverageAnnualReturnInceptionDate Jan. 09, 2008
DFA Selectively Hedged Global Fixed Income Portfolio | Return After Taxes on Distributions | Institutional Class
  
Risk/Return: rr_RiskReturnAbstract  
One Year rr_AverageAnnualReturnYear01 3.33%
Since Inception rr_AverageAnnualReturnSinceInception 1.52%
Inception Date rr_AverageAnnualReturnInceptionDate Jan. 09, 2008
DFA Selectively Hedged Global Fixed Income Portfolio | Return After Taxes on Distributions and Sale of Portfolio Shares | Institutional Class
  
Risk/Return: rr_RiskReturnAbstract  
One Year rr_AverageAnnualReturnYear01 2.74%
Since Inception rr_AverageAnnualReturnSinceInception 1.44%
Inception Date rr_AverageAnnualReturnInceptionDate Jan. 09, 2008
DFA Selectively Hedged Global Fixed Income Portfolio | Citi World Government Bond Index, 1-3 Years, in USD Terms (Unhedged) (reflects no deduction for fees, expenses, or taxes on sales)
  
Risk/Return: rr_RiskReturnAbstract  
One Year rr_AverageAnnualReturnYear01 (0.77%)
Since Inception rr_AverageAnnualReturnSinceInception 2.96%