Label	Element	Value
Risk/Return:	rr_RiskReturnAbstract
Registrant Name	dei_EntityRegistrantName	DFA INVESTMENT DIMENSIONS GROUP INC
Prospectus Date	rr_ProspectusDate	Feb. 28, 2013
Institutional Shares | DIMENSIONAL RETIREMENT FIXED INCOME FUND III
Risk/Return:	rr_RiskReturnAbstract
Risk/Return [Heading]	rr_RiskReturnHeading	Dimensional Retirement Fixed Income Fund III
Objective [Heading]	rr_ObjectiveHeading	INVESTMENT OBJECTIVE
Objective, Primary [Text Block]	rr_ObjectivePrimaryTextBlock	The investment objective of the Dimensional Retirement Fixed Income Fund III (the “Retirement Fixed Income Portfolio III”) is to seek to provide total return consistent with inflation protected long-term instruments. 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 Retirement Fixed Income Portfolio III.
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 Retirement Fixed Income Portfolio III 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. For the period March 7, 2012 (commencement of operations) to October 31, 2012, the Retirement Fixed Income Portfolio III’s 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 Narrative [Text Block]	rr_ExpenseExampleNarrativeTextBlock	This Example is meant to help you compare the cost of investing in the Retirement Fixed Income Portfolio III 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 Retirement Fixed Income Portfolio III reflect the net expenses of the Portfolio that result from the contractual expense waiver 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 securities from that universe to form a portfolio with the desired term exposure. The Retirement Fixed Income Portfolio III seeks its investment objective by generally investing in a universe of long-term fixed income securities structured to provide protection against inflation. The Retirement Fixed Income Portfolio III may invest in inflation-protected securities issued by the U.S. Government and its agencies and instrumentalities. The Retirement Fixed Income Portfolio III also may invest in inflation protected securities of other investment grade issuers including foreign governments and U.S. and non-U.S. corporations. 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 Retirement Fixed Income Portfolio III will purchase long-term fixed income securities with maturities greater than ten years, although it is anticipated that, at times, the Retirement Fixed Income Portfolio III will purchase securities with lesser maturities. The Retirement Fixed Income Portfolio III ordinarily will have an average weighted maturity, based upon market values, of greater than ten years. The Retirement Fixed Income Portfolio III also may invest in securities issued by the U.S. Government and its agencies and other investment grade issuers that do not provide inflation protection while protecting for inflation risk by engaging in swaps, futures or other derivatives. As a non-fundamental policy, under normal circumstances, at least 80% of the Retirement Fixed Income Portfolio III's net assets will be invested in fixed income securities. The Retirement Fixed Income Portfolio III 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 Retirement Fixed Income Portfolio III will not shift the maturity of its investments in anticipation of interest rate movements. The Retirement Fixed Income Portfolio III 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 Retirement Fixed Income Portfolio III 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 Retirement Fixed Income Portfolio III'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 Retirement Fixed Income Portfolio III 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 Retirement Fixed Income Portfolio III's income to decline. 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). 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. 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. The use of derivatives for non-hedging purposes may be considered more speculative than other types of investments. When the Retirement Fixed Income Portfolio III uses derivatives, the Portfolio will be directly exposed to the risks of those derivatives. 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. Additional risks are associated with the use of swaps including counterparty and credit risk (the risk that the other party to a swap agreement will not fulfill its contractual obligations, whether because of bankruptcy or other default) and liquidity risk (the possible lack of a secondary market for the swap agreement). 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 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. To the extent that the Portfolio holds securities directly and lends those securities, it will be also subject to the foregoing risks with respect to its loaned securities.
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	Performance information is not available for the Retirement Fixed Income Portfolio III because it has less than one calendar year of performance. Updated performance information for the Portfolio can be obtained in the future by visiting www.dimensional.com.
Performance One Year or Less [Text]	rr_PerformanceOneYearOrLess	Performance information is not available for the Retirement Fixed Income Portfolio III because it has less than one calendar year of performance.
Performance Availability Website Address [Text]	rr_PerformanceAvailabilityWebSiteAddress	www.dimensional.com
Institutional Shares | DIMENSIONAL RETIREMENT FIXED INCOME FUND III | Institutional Class
Risk/Return:	rr_RiskReturnAbstract
Shareholder Fees (fees paid directly from your investment)	rr_ShareholderFeeOther	none
Management Fee	rr_ManagementFeesOverAssets	0.30%
Other Expenses	rr_OtherExpensesOverAssets	29.35%
Total Annual Fund Operating Expenses	rr_ExpensesOverAssets	29.65%
Fee Waiver and/or Expense Reimbursement or (Recovery)	rr_FeeWaiverOrReimbursementOverAssets	29.25%	[1]
Total Annual Fund Operating Expenses After Fee Waiver and/or Expense Reimbursement or (Recovery)	rr_NetExpensesOverAssets	0.40%
1 Year	rr_ExpenseExampleYear01	41
3 Years	rr_ExpenseExampleYear03	4,809
5 Years	rr_ExpenseExampleYear05	7,516
10 Years	rr_ExpenseExampleYear10	10,208

[1] Pursuant to an Amended and Restated Fee Waiver and Expense Assumption Agreement for the Retirement Fixed Income Portfolio III, the Advisor has contractually agreed to waive up to the full amount of the Retirement Fixed Income Portfolio III's management fee of 0.30% to the extent necessary to offset the proportionate share of the management fees paid by the Retirement Fixed Income Portfolio III through its investment in other funds managed by the Advisor (the "Underlying Funds") (including the Portfolio's proportionate share of any management fees that an Underlying Fund paid through its investment in an affiliated cash management fund). In addition, under the Amended and Restated Fee Waiver and Expense Assumption Agreement, the Advisor has also agreed to waive all or a portion of the management fee and to assume the expenses of a class of the Retirement Fixed Income Portfolio III to the extent necessary to reduce the ordinary operating expenses (including expenses incurred through its investment in other investment companies but excluding any applicable 12b-1 fees) ("Portfolio Expenses") of a class of the Retirement Fixed Income Portfolio III so that such Portfolio Expenses do not exceed 0.40% of the average net assets of a class of the Portfolio on an annualized basis. The Amended and Restated Fee Waiver and Expense Assumption Agreement for the Retirement Fixed Income Portfolio III will remain in effect through February 28, 2014, and may not be terminated by the Advisor prior to that date.