Label

Element

Value

Risk/Return:

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Registrant Name

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DFA INVESTMENT DIMENSIONS GROUP INC

Prospectus Date

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Feb. 28, 2015

CONTINENTAL SMALL COMPANY PORTFOLIO

Risk/Return:

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Risk/Return [Heading]

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Continental Small Company Portfolio

Objective [Heading]

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INVESTMENT OBJECTIVE

Objective, Primary [Text Block]

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The investment objective of the Continental Small Company Portfolio is to achieve long-term capital appreciation. The Continental Small Company Portfolio is a Feeder Portfolio and pursues its objective by investing substantially all of its assets in its corresponding Master Fund, The Continental Small Company Series (the “Continental Small Company Series”) of The DFA Investment Trust Company (the “Trust”), which has the same investment objective and policies as the Portfolio.

Expense [Heading]

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FEES AND EXPENSES OF THE PORTFOLIO

Expense Narrative [Text Block]

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This table describes the fees and expenses you may pay if you buy and hold shares of the Continental Small Company Portfolio.

Shareholder Fees Caption [Text]

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Shareholder Fees (fees paid directly from your investment):

Operating Expenses Caption [Text]

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Annual Fund Operating Expenses (expenses that you pay each year as a percentage of the value of your investment)

Portfolio Turnover [Heading]

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Portfolio Turnover

Portfolio Turnover [Text Block]

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The Continental Small Company Series 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 Continental Small Company Portfolio’s performance. During the most recent fiscal year, the Continental Small Company Series’ portfolio turnover rate was 13% of the average value of its investment portfolio.

Portfolio Turnover, Rate

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13.00%

Expenses Represent Both Master and Feeder [Text]

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The “Management Fee” includes an investment management fee payable by the Continental Small Company Series and an administration fee payable by the Continental Small Company Portfolio. The amounts set forth under “Other Expenses” and “Total Annual Fund Operating Expenses” reflect the direct expenses of the Continental Small Company Portfolio and the indirect expenses of the Portfolio’s portion of the expenses of the Continental Small Company Series.

Expense Example [Heading]

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Example

Expense Example Narrative [Text Block]

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This Example is meant to help you compare the cost of investing in the Continental Small Company 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:

Expense Example Closing [Text Block]

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The Example reflects the aggregate estimated annual operating expenses of the Continental Small Company Portfolio and the Continental Small Company Portfolio’s portion of the expenses of the Continental Small Company Series.

Strategy [Heading]

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PRINCIPAL INVESTMENT STRATEGIES

Strategy Narrative [Text Block]

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The Continental Small Company Portfolio pursues its investment objective by investing substantially all of its assets in the Continental Small Company Series. The Continental Small Company Series, using a market capitalization weighted approach, purchases a broad and diverse group of readily marketable securities of small companies associated with European countries designated by Dimensional Fund Advisors LP (the “Advisor”) as approved markets for investment. A company’s market capitalization is the number of its shares outstanding times its price per share. In general, the higher the relative market capitalization of a small company within an eligible country, the greater its representation in the Series. The Advisor may modify market capitalization weights and even exclude companies after considering such factors as free float, momentum, trading strategies, liquidity management, and profitability, as well as 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.

As a non-fundamental policy, under normal circumstances, the Continental Small Company Series will invest at least 80% of its net assets in securities of small companies located in continental Europe. The Advisor determines the maximum market capitalization of a small company with respect to each country or region in which the Series invests. As of December 31, 2014, for the Continental Small Company Series, the highest maximum market capitalization of a small company in any country or region in which the Continental Small Company Series invests was $4,992 million. This threshold will change due to market conditions. The Continental Small Company Series also may invest up to 20% of its net assets in small companies associated with non-European countries that the Advisor has identified as approved markets for investment.

The Continental Small Company Series 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 Continental Small Company Series and the Continental Small Company Portfolio each may use derivatives, such as futures contracts and options on futures contracts for continental European equity securities and indices 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 Series or Portfolio. The Series and Portfolio do not intend to use derivatives for purposes of speculation or leveraging investment returns.

The Continental Small Company Series may lend its portfolio securities to generate additional income.

Risk [Heading]

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PRINCIPAL RISKS

Risk Narrative [Text Block]

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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 Continental Small Company Series does not hedge foreign currency risk.

European Market Risk: Because the Continental Small Company Series concentrates investments in European countries, the Continental Small Company Portfolio’s performance is expected to be closely tied to the social, political and economic conditions within such European countries and to be more volatile than the performance of funds with more geographically diverse investments.

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.

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 Continental Small Company Series that owns them, and, in turn, the Continental Small Company Portfolio itself, to rise or fall. Because the value of your investment in the Portfolio will fluctuate, there is the risk that you will lose money.

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. The use of derivatives for non-hedging purposes may be considered more speculative than other types of investments. When the Continental Small Company Series and the Continental Small Company Portfolio use derivatives, the Continental Small Company 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 Continental Small Company Series may lose money and there may be a delay in recovering the loaned securities. The Continental Small Company Series 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]

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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]

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PERFORMANCE

Performance Narrative [Text Block]

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The bar chart and table immediately following illustrate the variability of the Continental Small Company 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 Continental Small Company Portfolio’s performance from year to year. The table illustrates how annualized one year, five year and ten year returns, both before and after taxes, compare with those of a broad measure of market performance. The Continental Small Company 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 Continental Small Company 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]

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The bar chart and table immediately following illustrate the variability of the Continental Small Company 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 Continental Small Company Portfolio’s performance from year to year.

Performance Availability Website Address [Text]

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http://us.dimensional.com

Performance Past Does Not Indicate Future [Text]

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The Continental Small Company Portfolio’s past performance (before and after taxes) is not an indication of future results.

Bar Chart [Heading]

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Continental Small Company Portfolio Institutional Class Shares
Total Returns (%)

Bar Chart Closing [Text Block]

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January 2005-December 2014

Highest Quarter	Lowest Quarter
31.47 (4/09-6/09)	-28.18 (7/11-9/11)

Performance Table Heading

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Periods ending December 31, 2014
Annualized Returns (%)

Performance Table Uses Highest Federal Rate

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The after-tax returns presented in the table for the Continental Small Company 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

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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.

CONTINENTAL SMALL COMPANY PORTFOLIO | INSTITUTIONAL CLASS

Risk/Return:

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Shareholder Fees (fees paid directly from your investment)

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none

Management Fee

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0.50%

^[1]

Other Expenses

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0.06%

^[1]

Total Annual Fund Operating Expenses

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0.56%

^[1]

1 Year

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57

3 Years

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179

5 Years

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313

10 Years

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701

2005

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18.40%

2006

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45.83%

2007

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9.45%

2008

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(47.96%)

2009

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44.33%

2010

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16.57%

2011

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(23.48%)

2012

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21.93%

2013

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39.33%

2014

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(7.78%)

Highest Quarterly Return, Label

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Highest Quarter

Highest Quarterly Return, Date

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Jun. 30, 2009

Highest Quarterly Return

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31.47%

Lowest Quarterly Return, Label

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Lowest Quarter

Lowest Quarterly Return, Date

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Sep. 30, 2011

Lowest Quarterly Return

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(28.18%)

One Year

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(7.78%)

Five Years

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6.92%

Ten Years

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7.09%

CONTINENTAL SMALL COMPANY PORTFOLIO | Return After Taxes on Distributions | INSTITUTIONAL CLASS

Risk/Return:

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One Year

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(8.28%)

Five Years

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6.34%

Ten Years

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6.35%

CONTINENTAL SMALL COMPANY PORTFOLIO | Return After Taxes on Distributions and Sale of Portfolio Shares | INSTITUTIONAL CLASS

Risk/Return:

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One Year

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(4.04%)

Five Years

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5.35%

Ten Years

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5.78%

CONTINENTAL SMALL COMPANY PORTFOLIO | MSCI Europe ex UK Small Cap Index (net dividends) (reflects no deduction for fees, expenses, or taxes on sales)

Risk/Return:

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One Year

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(6.96%)

Five Years

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7.69%

Ten Years

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7.69%

[1] The "Management Fee" includes an investment management fee payable by the Continental Small Company Series and an administration fee payable by the Continental Small Company Portfolio. The amounts set forth under "Other Expenses" and "Total Annual Fund Operating Expenses" reflect the direct expenses of the Continental Small Company Portfolio and the indirect expenses of the Portfolio's portion of the expenses of the Continental Small Company Series.