Objective, Primary [Text Block]

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Risk/Return [Heading]

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SMALL COMPANY GROWTH PORTFOLIO

Objective [Heading]

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Objective

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The Small Company Growth Portfolio seeks long-term capital appreciation by investing primarily in growth-oriented equity securities of small capitalization companies.

Expense [Heading]

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Fees and Expenses

Expense Narrative [Text Block]

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The table below describes the fees and expenses that you may pay if you buy and hold Class IS shares of the 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 Portfolio 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 Portfolio pays transaction costs, such as commissions, when it buys and sells securities (or "turns over" its portfolio). A higher portfolio turnover rate 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 Total Annual Portfolio Operating Expenses or in the Example, affect Portfolio performance. During the most recent fiscal year, the Portfolio's portfolio turnover rate was 22% of the average value of its portfolio.

Portfolio Turnover, Rate

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22.00%

Other Expenses, New Fund, Based on Estimates [Text]

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Other expenses have been estimated for the current fiscal year.

Expense Example [Heading]

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Example

Expense Example Narrative [Text Block]

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The example below is intended to help you compare the cost of investing in the Portfolio with the cost of investing in other mutual funds.

The example assumes that you invest $10,000 in the Portfolio, 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]

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Principal Investment Strategies

Strategy Narrative [Text Block]

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Under normal market conditions, the Adviser seeks to achieve the Portfolio's investment objective by investing primarily in established and emerging companies from a universe comprised of small capitalization companies, most with market capitalizations of generally less than $4 billion.

Under normal circumstances, at least 80% of the Portfolio's assets will be invested in equity securities of small capitalization companies. This policy may be changed without shareholder approval; however, you would be notified in writing of any changes. A company is considered to be a small capitalization company if it has a total market capitalization at the time of purchase of $4 billion or less.

The Adviser emphasizes a bottom-up stock selection process, seeking attractive investments on an individual company basis. In selecting securities for investment, the Adviser seeks to invest in high quality companies it believes have sustainable competitive advantages and the ability to redeploy capital at high rates of return. The Adviser typically favors companies with rising returns on invested capital, above average business visibility, strong free cash flow generation and an attractive risk/reward. The Adviser generally considers selling an investment when it determines the company no longer satisfies its investment criteria.

The Portfolio's equity investments may include common and preferred stocks, convertible securities and equity-linked securities, rights and warrants to purchase common stocks, depositary receipts, exchange-traded funds ("ETFs"), limited partnership interests and other specialty securities having equity features. The Portfolio may invest in privately placed and restricted securities.

The Adviser may invest up to 25% of the Portfolio's net assets in foreign securities, including emerging market securities, and securities classified as American Depositary Receipts ("ADRs"), Global Depositary Receipts ("GDRs"), American Depositary Shares ("ADSs") or Global Depositary Shares ("GDSs"), foreign U.S. dollar-denominated securities that are traded on a U.S. exchange or local shares of non-U.S. issuers.

The Portfolio may utilize foreign currency forward exchange contracts, which are derivatives, in connection with its investments in foreign securities.

Risk [Heading]

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Principal Risks

Risk Narrative [Text Block]

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There is no assurance that the Portfolio will achieve its investment objective and you can lose money investing in this Portfolio. The principal risks of investing in the Portfolio include:

• Equity Securities. In general, prices of equity securities are more volatile than those of fixed income securities. The prices of equity securities fluctuate, and sometimes widely fluctuate, in response to activities specific to the issuer of the security as well as factors unrelated to the fundamental condition of the issuer, including general market, economic and political conditions. To the extent that the Portfolio invests in convertible securities, and the convertible security's investment value is greater than its conversion value, its price will be likely to increase when interest rates fall and decrease when interest rates rise. If the conversion value exceeds the investment value, the price of the convertible security will tend to fluctuate directly with the price of the underlying equity security.

• Foreign and Emerging Market Securities. Investments in foreign markets entail special risks such as currency, political, economic and market risks. There also may be greater market volatility, less reliable financial information, higher transaction and custody costs, decreased market liquidity and less government and exchange regulation associated with investments in foreign markets. In addition, investments in certain foreign markets, which have historically been considered stable, may become more volatile and subject to increased risk due to ongoing developments and changing conditions in such markets. Moreover, the growing interconnectivity of global economies and financial markets has increased the probability that adverse developments and conditions in one country or region will affect the stability of economies and financial markets in other countries or regions. The risks of investing in emerging market countries are greater than risks associated with investments in foreign developed countries. In addition, the Portfolio's investments may be denominated in foreign currencies and therefore, to the extent unhedged, the value of the investment will fluctuate with the U.S. dollar exchange rates. To the extent hedged by use of foreign currency forward exchange contracts, the precise matching of foreign currency forward exchange contract amounts and the value of the securities involved will not generally be possible because the future value of such securities in foreign currencies will change as a consequence of market movements in the value of those securities between the date on which the contract is entered into and the date it matures. There is additional risk that such transactions reduce or preclude the opportunity for gain if the value of the currency should move in the direction opposite to the position taken and that foreign currency forward exchange contracts create exposure to currencies in which the Portfolio's securities are not denominated. The use of foreign currency forward exchange contracts involves the risk of loss from the insolvency or bankruptcy of the counterparty to the contract or the failure of the counterparty to make payments or otherwise comply with the terms of the contract.

• Small Cap Companies. Investments in small cap companies may involve greater risks than those associated with larger, more established companies. The securities issued by small cap companies may be less liquid, and such companies may have more limited markets, financial resources and product lines, and may lack the depth of management of larger companies.

• Privately Placed and Restricted Securities. The Portfolio's investments may also include privately placed securities, which are subject to resale restrictions. These securities will have the effect of increasing the level of Portfolio illiquidity to the extent the Portfolio may be unable to sell or transfer these securities due to restrictions on transfers or on the ability to find buyers interested in purchasing the securities. The illiquidity of the market, as well as the lack of publicly available information regarding these securities, may also adversely affect the ability to arrive at a fair value for certain securities at certain times and could make it difficult for the Portfolio to sell certain securities.

Shares of the Portfolio are not bank deposits and are not guaranteed or insured by the Federal Deposit Insurance Corporation or any other government agency.

Risk Lose Money [Text]

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There is no assurance that the Portfolio will achieve its investment objective and you can lose money investing in this Portfolio.

Risk Not Insured Depository Institution [Text]

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Shares of the Portfolio are not bank deposits and are not guaranteed or insured by the Federal Deposit Insurance Corporation or any other government agency.

Bar Chart and Performance Table [Heading]

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Performance Information

Performance Narrative [Text Block]

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The bar chart and table below provide some indication of the risks of investing in the Portfolio by showing changes in the Portfolio's Class I shares' performance from year-to-year and by showing how the Portfolio's average annual returns for the past one, five and 10 year periods compare with those of a broad measure of market performance, as well as an index that represents a group of similar mutual funds, over time. The performance of the Class IS shares will differ because the Class IS shares have different ongoing fees. The Portfolio's past performance, before and after taxes, is not necessarily an indication of how the Portfolio will perform in the future. Updated performance information is available online at www.morganstanley.com/im.

Performance Information Illustrates Variability of Returns [Text]

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Performance Availability Website Address [Text]

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www.morganstanley.com/im

Performance Past Does Not Indicate Future [Text]

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The Portfolio's past performance, before and after taxes, is not necessarily an indication of how the Portfolio will perform in the future.

Bar Chart [Heading]

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Annual Total Returns-Calendar Years (Class I)*

Bar Chart Footnotes [Text Block]

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High Quarter				6/30/09					25.00	%
Low Quarter				12/31/08					–23.08	%

Bar Chart Closing [Text Block]

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* Class I shares are not offered in this Prospectus. As of the date of this Prospectus, the Fund had not commenced offering Class IS shares of the Portfolio. Class IS shares would have substantially similar annual returns because the shares are invested in the same portfolio of securities and the annual returns would differ only to the extent that the Classes do not have the same expenses. The returns for Class IS shares are expected to be higher than the returns for Class I shares of the Portfolio as expenses of Class IS are estimated to be lower. Return information for the Portfolio's Class IS shares will be shown in future prospectuses offering the Portfolio's Class IS shares after the Portfolio's Class IS shares have a full calendar year of return information to report.

Bar Chart, Returns for Class Not Offered in Prospectus [Text]

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Class I shares are not offered in this Prospectus.

Highest Quarterly Return, Label

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High Quarter

Highest Quarterly Return, Date

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Jun. 30, 2009

Highest Quarterly Return

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25.00%

Lowest Quarterly Return, Label

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Low Quarter

Lowest Quarterly Return, Date

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Dec. 31, 2008

Lowest Quarterly Return

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(23.08%)

Index No Deduction for Fees, Expenses, Taxes [Text]

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(reflects no deduction for fees, expenses or taxes)

Performance Table Uses Highest Federal Rate

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Performance Table Not Relevant to Tax Deferred

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Actual after-tax returns depend on the investor's tax situation and may differ from those shown, and after-tax returns are not relevant to investors who hold their Portfolio shares through tax deferred arrangements such as 401(k) plans or individual retirement accounts.

Performance Table One Class of after Tax Shown [Text]

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After-tax returns for the Portfolio's Class IS shares will vary from Class I shares' returns.

Performance Table Explanation after Tax Higher

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After-tax returns may be higher than before-tax returns due to an assumed benefit from capital losses that would have been realized had Portfolio shares been sold at the end of the relevant periods, as applicable.

Performance Table Closing [Text Block]

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The after-tax returns shown in the table above are calculated using the historical highest individual federal marginal income tax rates during the period shown and do not reflect the impact of state and local taxes. After-tax returns for the Portfolio's Class IS shares will vary from Class I shares' returns. Actual after-tax returns depend on the investor's tax situation and may differ from those shown, and after-tax returns are not relevant to investors who hold their Portfolio shares through tax deferred arrangements such as 401(k) plans or individual retirement accounts. After-tax returns may be higher than before-tax returns due to an assumed benefit from capital losses that would have been realized had Portfolio shares been sold at the end of the relevant periods, as applicable.

Caption

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Average Annual Total Returns (for the calendar periods ended December 31, 2012)

Russell 2000® Growth Index (reflects no deduction for fees, expenses or taxes)

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14.59%

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rr_AverageAnnualReturnYear05

3.49%

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rr_AverageAnnualReturnYear10

9.80%

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rr_AverageAnnualReturnSinceInception

6.74%

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Lipper Small-Cap Growth Funds Index (reflects no deduction for taxes)

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rr_AverageAnnualReturnYear01

14.95%

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rr_AverageAnnualReturnYear05

2.09%

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rr_AverageAnnualReturnYear10

8.56%

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rr_AverageAnnualReturnSinceInception

8.58%

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Class IS

Redemption Fee (as a percentage of Amount Redeemed)

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(2.00%)

Advisory Fee

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0.90%

Distribution and/or Shareholder Service (12b-1) Fee

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none

Other Expenses

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0.13%

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Total Annual Portfolio Operating Expenses

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1.03%

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Fee Waiver or Reimbursement

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(0.05%)

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Total Annual Portfolio Operating Expenses After Fee Waiver and/or Expense Reimbursement

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0.98%

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Expense Example, with Redemption, 1 Year

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$ 100

Expense Example, with Redemption, 3 Years

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$ 312

Performance One Year or Less [Text]

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As of the date of this Prospectus, the Fund had not commenced offering Class IS shares of the Portfolio.

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CLASS I

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Annual Return 2003

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44.13%

Annual Return 2004

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19.17%

Annual Return 2005

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13.55%

Annual Return 2006

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11.90%

Annual Return 2007

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3.04%

Annual Return 2008

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(41.84%)

Annual Return 2009

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47.92%

Annual Return 2010

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27.20%

Annual Return 2011

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(9.12%)

Annual Return 2012

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17.10%

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17.10%

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rr_AverageAnnualReturnYear05

3.09%

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rr_AverageAnnualReturnYear10

10.10%

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Average Annual Returns, Inception Date

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10.67%

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Nov. 01, 1989

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CLASS I | After Taxes on Distributions

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rr_AverageAnnualReturnYear01

16.28%

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2.85%

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rr_AverageAnnualReturnYear10

9.53%

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rr_AverageAnnualReturnSinceInception

8.36%

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CLASS I | After Taxes on Distributions and Sale of Portfolio Shares

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rr_AverageAnnualReturnYear01

12.06%

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rr_AverageAnnualReturnYear05

2.62%

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rr_AverageAnnualReturnYear10

8.89%

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