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Risk/Return: rr_RiskReturnAbstract  
Registrant Name dei_EntityRegistrantName DFA INVESTMENT DIMENSIONS GROUP INC
Prospectus Date rr_ProspectusDate Feb. 28, 2013
R10R25 Shares | DFA Inflation-Protected Securities Portfolio
  
Risk/Return: rr_RiskReturnAbstract  
Risk/Return [Heading] rr_RiskReturnHeading DFA Inflation-Protected Securities Portfolio
Objective [Heading] rr_ObjectiveHeading INVESTMENT OBJECTIVE
Objective, Primary [Text Block] rr_ObjectivePrimaryTextBlock The investment objective of the DFA Inflation-Protected Securities Portfolio (the “Inflation-Protected Portfolio”) is to provide inflation protection and earn current income consistent with inflation-protected securities.
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 Class R25 shares of the Inflation-Protected 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 Inflation-Protected 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 9% of the average value of its investment portfolio.
Portfolio Turnover, Rate rr_PortfolioTurnoverRate 9.00%
Other Expenses, New Fund, Based on Estimates [Text] rr_OtherExpensesNewFundBasedOnEstimates The Class R25 shares are a new class of shares of the Portfolio, so the “Other Expenses” shown for the class are based on anticipated fees and expenses for the first full fiscal year.
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 Inflation-Protected 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 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 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 range of portfolio securities that result in the Portfolio maintaining similar characteristics to the whole universe of eligible securities. The Advisor also places priority on efficiently managing portfolio turnover and keeping trading costs low.

The Inflation-Protected Portfolio seeks its investment objective by investing in a universe of inflation-protected securities that are structured to provide returns that at least keep up with the rate of inflation over the long-term. The Inflation-Protected Portfolio ordinarily invests in inflation-protected securities issued by the U.S. government and its agencies and instrumentalities and the credit quality such inflation-protected securities will be that of such applicable U.S. government, agency or instrumentality issuer.

As a non-fundamental policy, under normal circumstances, the Portfolio will invest at least 80% of its net assets in inflation-protected securities. Inflation-protected securities (also known as inflation-indexed securities) are securities whose principal and/or interest payments are adjusted for inflation, unlike conventional debt securities that make fixed principal and interest payments. Inflation-protected securities include Treasury Inflation-Protected Securities ("TIPS"), which are securities issued by the U.S. Treasury. The principal value of TIPS is adjusted for inflation (payable at maturity) and the semi-annual interest payments by TIPS equal a fixed percentage of the inflation-adjusted principal amount. These inflation adjustments are based upon the Consumer Price Index for Urban Consumers (CPI-U). The original principal value of TIPS is guaranteed, even during periods of deflation. At maturity, TIPS are redeemed at the greater of their inflation-adjusted principal or par amount at original issue. Other types of inflation-protected securities may use other methods to adjust for inflation and other measures of inflation. In addition, inflation-protected securities issued by entities other than the U.S. Treasury may not provide a guarantee of principal value at maturity.

Generally, the Inflation-Protected Portfolio will purchase inflation-protected securities with maturities of between five and twenty years from the date of settlement, although it is anticipated that, at times, the Portfolio will purchase securities outside of this range. The Portfolio ordinarily will have an average weighted maturity, based upon market values, of between three to twelve years.

The Inflation-Protected Portfolio is authorized to invest more than 25% of its total assets in Treasury bonds, bills and notes and obligations of U.S. government agencies and instrumentalities. The Portfolio will not shift the maturity of its investments in anticipation of interest rate movements.

The Inflation-Protected Portfolio may lend its portfolio securities to generate additional income.
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 Inflation-Protected 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.

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.

Inflation-Protected Securities Interest Rate Risk: Inflation-protected securities may react differently from other fixed income securities to changes in interest rates. Because interest rates on inflation-protected securities are adjusted for inflation, the values of these securities are not materially affected by inflation expectations. Therefore, the value of inflation-protected securities are anticipated to change in response to changes in "real" interest rates, which represent nominal (stated) interest rates reduced by the expected impact of inflation. Generally, the value of an inflation-protected security will fall when real interest rates rise and will rise when real interest rates fall.

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 Inflation-Protected 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 Investing for Inflation Protection: Because the interest and/or principal payments on an inflation-protected security are adjusted periodically for changes in inflation, the income distributed by the Inflation-Protected Portfolio may be irregular. Although the U.S. Treasury guarantees to pay at least the original face value of any inflation-protected securities the Treasury issues, other issuers may not offer the same guarantee. Also, inflation-protected securities, including those issued by the U.S. Treasury, are not protected against deflation. As a result, in a period of deflation, the inflation-protected securities held by the Portfolio may not pay any income and the Portfolio may suffer a loss during such periods. While inflation-protected securities are expected to be protected from long-term inflationary trends, short-term increases in inflation may lead to a decline in the Portfolio's value. If interest rates rise due to reasons other than inflation, the Portfolio's investment in these securities may not be protected to the extent that the increase is not reflected in the securities' inflation measures. In addition, positive adjustments to principal generally will result in taxable income to the Portfolio at the time of such adjustments (which generally would be distributed by the Portfolio as part of its taxable dividends), even though the principal amount is not paid until maturity. The current market value of inflation-protected securities is not guaranteed and will fluctuate.

Income Risk: Income risk is the risk that falling interest rates will cause the Inflation-Protected Portfolio's income to decline.

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 Inflation-Protected Portfolio may lose money and there may be a delay in recovering the loaned securities. The 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 Inflation-Protected Portfolio’s returns and are meant to provide some indication of the risks of investing in the Portfolio. The Class R25 shares of the Portfolio are a new class of shares for which performance information is not available; therefore, the bar chart and table show performance information for the Institutional Class shares of the Portfolio, another class of shares of the Portfolio not offered in this Prospectus. The bar chart shows the changes in performance of the Institutional Class shares of the Portfolio from year to year. The table illustrates how annualized one year and since inception returns of the Institutional Class shares of the Portfolio compare with those of a broad measure of market performance. The Inflation-Protected 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.
Performance Information Illustrates Variability of Returns [Text] rr_PerformanceInformationIllustratesVariabilityOfReturns The bar chart and table immediately following illustrate the variability of the Inflation-Protected Portfolio’s returns and are meant to provide some indication of the risks of investing in the Portfolio. The Class R25 shares of the Portfolio are a new class of shares for which performance information is not available; therefore, the bar chart and table show performance information for the Institutional Class shares of the Portfolio, another class of shares of the Portfolio not offered in this Prospectus. The bar chart shows the changes in performance of the Institutional Class shares of the Portfolio from year to year.
Performance Availability Website Address [Text] rr_PerformanceAvailabilityWebSiteAddress www.dimensional.com
Performance Past Does Not Indicate Future [Text] rr_PerformancePastDoesNotIndicateFuture The Inflation-Protected Portfolio’s past performance (before and after taxes) is not an indication of future results.
Bar Chart [Heading] rr_BarChartHeading DFA Inflation-Protected Securities Portfolio Institutional Class Shares
Total Returns (%)
Bar Chart Closing [Text Block] rr_BarChartClosingTextBlock January 2007-December 2012

Highest Quarter    Lowest Quarter
6.31 (1/08-3/08)    -4.00 (7/08-9/08)
Bar Chart, Returns for Class Not Offered in Prospectus [Text] rr_BarChartReturnsForClassNotOfferedInProspectus The Class R25 shares of the Portfolio are a new class of shares for which performance information is not available; therefore, the bar chart and table show performance information for the Institutional Class shares of the Portfolio, another class of shares of the Portfolio not offered in this Prospectus.
Performance Table Heading rr_PerformanceTableHeading Periods ending December 31, 2012
Annualized Returns (%)
R10R25 Shares | DFA Inflation-Protected Securities Portfolio | Class R25
  
Risk/Return: rr_RiskReturnAbstract  
Shareholder Fees (fees paid directly from your investment) rr_ShareholderFeeOther none
Management Fee rr_ManagementFeesOverAssets 0.10%
Distribution and/or Service (12b-1) Fees rr_DistributionAndService12b1FeesOverAssets 0.25%
Other Expenses rr_OtherExpensesOverAssets 0.31% [1]
Total Annual Fund Operating Expenses rr_ExpensesOverAssets 0.66%
Fee Waiver and/or Expense Reimbursement or (Recovery) rr_FeeWaiverOrReimbursementOverAssets 0.21% [2]
Total Annual Fund Operating Expenses After Fee Waiver and/or Expense Reimbursement or (Recovery) rr_NetExpensesOverAssets 0.45%
1 Year rr_ExpenseExampleYear01 46
3 Years rr_ExpenseExampleYear03 190
R10R25 Shares | DFA Inflation-Protected Securities Portfolio | Institutional Class
  
Risk/Return: rr_RiskReturnAbstract  
2007 rr_AnnualReturn2007 11.84% [3]
2008 rr_AnnualReturn2008 (1.42%) [3]
2009 rr_AnnualReturn2009 11.01% [3]
2010 rr_AnnualReturn2010 6.81% [3]
2011 rr_AnnualReturn2011 14.55% [3]
2012 rr_AnnualReturn2012 7.45% [3]
Highest Quarterly Return, Label rr_HighestQuarterlyReturnLabel Highest Quarter
Highest Quarterly Return, Date rr_BarChartHighestQuarterlyReturnDate Mar. 31, 2008
Highest Quarterly Return rr_BarChartHighestQuarterlyReturn 6.31%
Lowest Quarterly Return, Label rr_LowestQuarterlyReturnLabel Lowest Quarter
Lowest Quarterly Return, Date rr_BarChartLowestQuarterlyReturnDate Sep. 30, 2008
Lowest Quarterly Return rr_BarChartLowestQuarterlyReturn (4.00%)
One Year rr_AverageAnnualReturnYear01 7.45% [3]
Five Years rr_AverageAnnualReturnYear05 7.55% [3]
Since Inception rr_AverageAnnualReturnSinceInception 7.77% [3]
Inception Date rr_AverageAnnualReturnInceptionDate Sep. 18, 2006 [3]
R10R25 Shares | DFA Inflation-Protected Securities Portfolio | Barclays Capital U.S. Treasury Inflation Protected Securities (TIPS) Index (Series-L) (reflects no deduction for fees, expenses, or taxes)
  
Risk/Return: rr_RiskReturnAbstract  
One Year rr_AverageAnnualReturnYear01 6.98%
Five Years rr_AverageAnnualReturnYear05 7.04%
Since Inception rr_AverageAnnualReturnSinceInception 7.40%
[1] The Class R25 shares are a new class of shares of the Portfolio, so the "Other Expenses" shown for the class are based on anticipated fees and expenses for the first full fiscal year.
[2] The Advisor has agreed to waive certain fees and in certain instances, assume certain expenses of the Portfolio. The Fee Waiver and Expense Assumption Agreement for the 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.
[3] The Institutional Class shares of the Portfolio would have substantially similar annual returns as the Class R25 shares because the shares are invested in the same portfolio securities. Returns for the Class R25 shares and Institutional Class shares will differ to the extent that the classes will have different expenses, and returns for the Class R25 shares would be expected to be lower than the returns of the Institutional Class shares to the extent that the Class R25 shares have higher expenses than the Institutional Class shares.