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Risk/Return: rr_RiskReturnAbstract  
Registrant Name dei_EntityRegistrantName DFA INVESTMENT DIMENSIONS GROUP INC
Prospectus Date rr_ProspectusDate Feb. 28, 2016
DFA California Short-Term Municipal Bond Portfolio  
Risk/Return: rr_RiskReturnAbstract  
Risk/Return [Heading] rr_RiskReturnHeading DFA California Short-Term Municipal Bond Portfolio
Objective [Heading] rr_ObjectiveHeading Investment Objective
Objective, Primary [Text Block] rr_ObjectivePrimaryTextBlock The investment objective of the DFA California Short-Term Municipal Bond Portfolio (the “California Short-Term Municipal Bond Portfolio”) is to seek to provide current income that is expected to be exempt from federal personal income taxes and California state personal income taxes.
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 California Short-Term Municipal Bond 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 California Short-Term Municipal Bond 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 23% of the average value of its investment portfolio.
Portfolio Turnover, Rate rr_PortfolioTurnoverRate 23.00%
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 California Short-Term Municipal Bond 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 California Short-Term Municipal Bond Portfolio seeks its investment objective by investing primarily in a universe of municipal securities issued by or on behalf of California state or local governments and their agencies, instrumentalities and regional governmental authorities, the interest on which is exempt from regular federal income tax and the state personal income tax of California. The Portfolio may also invest a portion of its assets in municipal securities issued by U.S. territories that are exempt from state taxation under federal law. Municipal securities in which the Portfolio may invest include, among others, revenue bonds, general obligation bonds, industrial development bonds, municipal lease obligations, commercial paper variable rate demand obligations and other instruments (including participation interests in such securities). The Portfolio intends to invest in municipal securities that in the opinion of bond counsel for the issuers and under current tax law provide interest that is exempt from California and federal personal income taxes. As a fundamental investment policy, under normal market conditions, the Portfolio will invest at least 80% of its net assets in municipal securities that pay interest exempt from federal personal income tax and the California state personal income taxes. The Portfolio does not currently intend to invest its assets in securities whose interest is subject to the federal alternative minimum tax.

Generally, the Portfolio will acquire obligations that mature within three years from the date of settlement, but substantial investments may be made in obligations maturing up to ten years from the date of settlement when greater returns are available, and in variable rate demand notes with longer maturities. Under normal circumstances, the Portfolio will maintain a dollar-weighted average portfolio maturity of three years or less. In making purchase decisions, if the anticipated maturity risk premium is greater for longer-term securities in the eligible maturity range, Dimensional Fund Advisors LP (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 Portfolio intends to maintain a dollar-weighted average credit quality equal to or better than the lower of: (i) a credit quality rating of AA by S&P or Aa2 by Moody’s Investor’s Services, Inc. (“Moody’s”) or AA by Fitch Ratings Ltd. or (ii) the credit quality of general obligation bonds issued by the state of California. For purposes of the above policy on dollar-weighted average credit quality, unrated securities may be included if such securities have been determined by the Advisor to be of comparable quality. If a security has been redeemed by the issuer at a date prior to the stated final maturity date for the purposes of the above maturity restriction, the early redemption date shall be considered the maturity date regardless of the stated final maturity.

Municipal securities are often issued to obtain funds for various public purposes, including the construction of a wide range of public facilities, such as bridges, highways, housing, hospitals, mass transportation facilities, schools, streets and public utilities, such as water and sewer works. Municipal securities include municipal leases, certificates of participation, municipal obligation components and municipal custody receipts. The Portfolio may invest more than 25% of its assets in municipal securities issued to finance projects in a particular segment of the bond market including, but not limited to, health care, housing, education, utilities, and transportation. The Portfolio also may invest more than 25% of its assets in industrial development bonds.

The California Short-Term Municipal Bond Portfolio may (1) purchase certain municipal securities that are insured, (2) invest in municipal securities secured by mortgages on single-family homes and multi-family projects, (3) invest in pre-refunded municipal securities, (4) purchase tax-exempt municipal securities on a “when-issued” basis and (5) use fixed income related futures and options contracts, credit default swaps, interest rate swaps and other types of derivatives to hedge against changes in interest rates. The Portfolio may also use derivatives, such as futures contracts and options on futures contracts, 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.

Although the Portfolio attempts to invest all of its assets in tax-exempt securities, it is possible, although not anticipated, that a portion of its assets may be invested in securities that pay taxable interest, including interest that may be subject to the federal alternative minimum tax. These investments could generate taxable income for shareholders.

The California Short-Term Municipal Bond Portfolio is primarily designed for investment by California taxpayers.
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 California Short-Term Municipal Bond 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 changes in interest rates.

Credit Risk: Credit risk is the risk that the issuer of a security, including a governmental entity, 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 California Short-Term Municipal Bond Portfolio’s performance. The ability of a municipal securities issuer to make payments could be affected by litigation, legislation or other political events or the bankruptcy of the issuer. Credit risk is greater for fixed income securities with ratings below investment grade (e.g., BB+ or below by S&P or Ba1 or below by Moody’s). Fixed income securities that are below investment grade involve high credit risk and are considered speculative. Below investment grade fixed income securities may also fluctuate in value more than higher quality fixed income securities and, during periods of market volatility, may be more difficult to sell at the time and price the Portfolio desires.

Income Risk: Income risk is the risk that falling interest rates will cause the California Short-Term Municipal Bond Portfolio’s income to decline because, among other reasons, the proceeds from maturing short-term securities in its portfolio may be reinvested in lower-yielding securities.

Tax Liability Risk: Tax liability risk is the risk that distributions by the California Short-Term Municipal Bond Portfolio become taxable to shareholders due to noncompliant conduct by a municipal bond issuer, unfavorable changes in federal or state tax laws, or adverse interpretations of tax laws by the Internal Revenue Service or state tax authorities or other factors. Such adverse interpretations or actions could cause interest from a security to become taxable, possibly retroactively, subjecting shareholders to increased tax liability. In addition, such adverse interpretations or actions could cause the value of a security, and therefore, the value of the Portfolio’s shares, to decline.

State-Specific Risk: Because the California Short-Term Municipal Bond Portfolio focuses its investments primarily in California municipal securities, the value of the Portfolio’s investments will be highly sensitive to events affecting the fiscal stability of the State of California and its agencies, municipalities, authorities and other instrumentalities that issue securities. Having a significant percentage of its assets invested in the securities of fewer issuers, particularly obligations of government issuers of a single state, could result in greater credit risk exposure to a smaller number of issuers due to economic, regulatory or political problems in California. Also, to the extent that the Portfolio makes significant investments in securities issued to finance projects in a particular segment of the California municipal securities market such focused investment may cause the value of the Portfolio’s shares to change more than the value of shares of funds that invest more broadly. The deterioration of California’s fiscal situation as a result of the economic recession that began in the first quarter of 2008 increases the risk of investing in California municipal securities, including the risk of potential issuer default, and also heightens the risk that the prices of California municipal securities will experience greater volatility. These risks are disclosed in more detail in the Portfolio’s Statement of Additional Information.

Derivatives Risk: Derivatives are instruments, such as futures 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 or cause losses if the market moves in a manner different from that anticipated by the Portfolio or if the cost of the derivative outweighs the benefit of the hedge. The use of derivatives for non-hedging purposes may be considered more speculative than other types of investments. When the California Short-Term Municipal Bond 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. Additionally, payments made or received by the California Short-Term Municipal Bond Portfolio under such derivatives may increase the amount of distributions taxable to you as ordinary income, increase or decrease the amount of capital gain distributions to you and/or decrease the amount available for distribution to you as exempt-interest dividends.

Liquidity Risk: Liquidity risk exists when particular portfolio investments are difficult to purchase or sell. To the extent that the California Short-Term Municipal Bond Portfolio holds illiquid investments, the Portfolio’s performance may be reduced due to an inability to sell the investments at opportune prices or times. Liquid portfolio investments may become illiquid or less liquid after purchase by the California Short-Term Municipal Bond Portfolio due to low trading volume, adverse investor perceptions and/or other market developments. Liquidity risk includes the risk that the California Short-Term Municipal Bond Portfolio will experience significant net redemptions at a time when it cannot find willing buyers for its portfolio securities or can only sell its portfolio securities at a material loss. Liquidity risk can be more pronounced in periods of market turmoil.

Cyber Security Risk: The California Short-Term Municipal Bond 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 California Short-Term Municipal Bond 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, five 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 http://us.dimensional.com.

The after-tax returns presented in the table for the California Short-Term Municipal Bond 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 California Short-Term Municipal Bond 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 http://us.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 California Short-Term Municipal Bond Portfolio Institutional Class Shares—Total Returns
Bar Chart Closing [Text Block] rr_BarChartClosingTextBlock January 2008-December 2015

Highest Quarter    Lowest Quarter
2.20% (10/08–12/08)    -0.95% (10/10–12/10)
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 California Short-Term Municipal Bond 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 California Short-Term Municipal Bond Portfolio | Institutional Class  
Risk/Return: rr_RiskReturnAbstract  
Shareholder Fees (fees paid directly from your investment) rr_ShareholderFeeOther none
Management Fee rr_ManagementFeesOverAssets 0.20%
Other Expenses rr_OtherExpensesOverAssets 0.02%
Total Annual Fund Operating Expenses rr_ExpensesOverAssets 0.22%
1 YEAR rr_ExpenseExampleYear01 $ 23
3 YEARS rr_ExpenseExampleYear03 71
5 YEARS rr_ExpenseExampleYear05 124
10 YEARS rr_ExpenseExampleYear10 $ 280
2008 rr_AnnualReturn2008 3.13%
2009 rr_AnnualReturn2009 3.92%
2010 rr_AnnualReturn2010 1.19%
2011 rr_AnnualReturn2011 2.68%
2012 rr_AnnualReturn2012 0.94%
2013 rr_AnnualReturn2013 0.65%
2014 rr_AnnualReturn2014 0.80%
2015 rr_AnnualReturn2015 1.02%
Highest Quarterly Return, Label rr_HighestQuarterlyReturnLabel Highest Quarter
Highest Quarterly Return, Date rr_BarChartHighestQuarterlyReturnDate Dec. 31, 2008
Highest Quarterly Return rr_BarChartHighestQuarterlyReturn 2.20%
Lowest Quarterly Return, Label rr_LowestQuarterlyReturnLabel Lowest Quarter
Lowest Quarterly Return, Date rr_BarChartLowestQuarterlyReturnDate Dec. 31, 2010
Lowest Quarterly Return rr_BarChartLowestQuarterlyReturn (0.95%)
1 YEAR rr_AverageAnnualReturnYear01 1.02%
5 YEARS rr_AverageAnnualReturnYear05 1.22%
SINCE INCEPTION rr_AverageAnnualReturnSinceInception 1.92%
INCEPTION DATE rr_AverageAnnualReturnInceptionDate Apr. 02, 2007
DFA California Short-Term Municipal Bond Portfolio | Return After Taxes on Distributions | Institutional Class  
Risk/Return: rr_RiskReturnAbstract  
1 YEAR rr_AverageAnnualReturnYear01 1.02%
5 YEARS rr_AverageAnnualReturnYear05 1.22%
SINCE INCEPTION rr_AverageAnnualReturnSinceInception 1.92%
INCEPTION DATE rr_AverageAnnualReturnInceptionDate Apr. 02, 2007
DFA California Short-Term Municipal Bond Portfolio | Return After Taxes on Distributions and Sale of Portfolio Shares | Institutional Class  
Risk/Return: rr_RiskReturnAbstract  
1 YEAR rr_AverageAnnualReturnYear01 0.93%
5 YEARS rr_AverageAnnualReturnYear05 1.19%
SINCE INCEPTION rr_AverageAnnualReturnSinceInception 1.85%
INCEPTION DATE rr_AverageAnnualReturnInceptionDate Apr. 02, 2007
DFA California Short-Term Municipal Bond Portfolio | BofA Merrill Lynch 1-3 Year California Including Puerto Rico Municipal Securities Index (reflects no deduction for fees, expenses, or taxes)  
Risk/Return: rr_RiskReturnAbstract  
1 YEAR rr_AverageAnnualReturnYear01 0.74% [1]
5 YEARS rr_AverageAnnualReturnYear05 1.18% [1]
SINCE INCEPTION rr_AverageAnnualReturnSinceInception 2.29% [1]
[1] Source Merrill Lynch, used with permission. MERRILL LYNCH IS LICENSING THE MERRILL LYNCH INDICES “AS IS,” MAKES NO WARRANTIES REGARDING SAME, DOES NOT GUARANTEE THE ACCURACY AND OR COMPLETENESS OF THE MERRILL LYNCH INDICES OR ANY DATA INCLUDED THEREIN OR DERIVED THEREFROM, AND ASSUMES NO LIABILITY IN CONNECTION WITH THEIR USE.