Label	Element	Value
Risk/Return:	rr_RiskReturnAbstract
Registrant Name	dei_EntityRegistrantName	BLACKROCK SERIES, INC.
Prospectus Date	rr_ProspectusDate	Sep. 29, 2014
BlackRock Small Cap Growth Fund II
Risk/Return:	rr_RiskReturnAbstract
Risk/Return [Heading]	rr_RiskReturnHeading	Fund Overview Key Facts About BlackRock Small Cap Growth Fund II
Objective [Heading]	rr_ObjectiveHeading	Investment Objective
Objective, Primary [Text Block]	rr_ObjectivePrimaryTextBlock	The investment objective of BlackRock Small Cap Growth Fund II (“Small Cap Growth” or the “Fund”), a series of BlackRock Series, Inc. (the “Corporation”), is to seek long-term capital growth. In other words, the Fund tries to choose investments that will increase in value. Current income from dividends and interest will not be an important consideration in selecting portfolio securities.
Expense [Heading]	rr_ExpenseHeading	Fees and Expenses of the Fund
Expense Narrative [Text Block]	rr_ExpenseNarrativeTextBlock	This table describes the fees and expenses that you may pay if you buy and hold shares of the Fund. You may qualify for sales charge discounts if you and your family invest, or agree to invest in the future, at least $25,000 in the fund complex advised by BlackRock Advisors, LLC (“BlackRock”) and its affiliates. More information about these and other discounts is available from your financial professional or your selected securities dealer, broker, investment adviser, service provider or industry professional (including BlackRock, The PNC Financial Services Group, Inc. and their respective affiliates) (each a “Financial Intermediary”) and in the “Details About the Share Classes” section on page 17 of the Fund’s prospectus and in the “Purchase of Shares” section on page II-61 of Part II of the Fund’s Statement of Additional Information.
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	October 1, 2015
Portfolio Turnover [Heading]	rr_PortfolioTurnoverHeading	Portfolio Turnover:
Portfolio Turnover [Text Block]	rr_PortfolioTurnoverTextBlock	The Master 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 shares are held in a taxable account. These costs, which are not reflected in annual Fund operating expenses or in the example, affect the Fund’s performance. During the most recent fiscal year, the Master Portfolio’s portfolio turnover rate was 152% of the average value of its portfolio.
Portfolio Turnover, Rate	rr_PortfolioTurnoverRate	152.00%
Expenses Deferred Charges [Text Block]	rr_ExpensesDeferredChargesTextBlock	A contingent deferred sales charge (“CDSC”) of 1.00% is assessed on certain redemptions of Investor A Shares made within 18 months after purchase where no initial sales charge was paid at time of purchase as part of an investment of $1,000,000 or more.
Expense Breakpoint Discounts [Text]	rr_ExpenseBreakpointDiscounts	You may qualify for sales charge discounts if you and your family invest, or agree to invest in the future, at least $25,000 in the fund complex advised by BlackRock Advisors, LLC (“BlackRock”) and its affiliates.
Expense Breakpoint, Minimum Investment Required [Amount]	rr_ExpenseBreakpointMinimumInvestmentRequiredAmount	$ 25,000
Expenses Represent Both Master and Feeder [Text]	rr_ExpensesRepresentBothMasterAndFeeder	The fees and expenses shown in the table and the example that follows include both the expenses of the Fund and the Fund’s share of the allocated expenses of BlackRock Master Small Cap Growth Portfolio (the “Master Portfolio”) of BlackRock Master LLC (the “Master LLC”). Management fees are paid by the Master Portfolio.
Expense Example [Heading]	rr_ExpenseExampleHeading	Example:
Expense Example Narrative [Text Block]	rr_ExpenseExampleNarrativeTextBlock	This Example is intended to help you compare the cost of investing in the Fund with the cost of investing in other mutual funds. The Example assumes that you invest $10,000 in the Fund 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 Fund’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, No Redemption, By Year, Caption [Text]	rr_ExpenseExampleNoRedemptionByYearCaption	You would pay the following expenses if you did not redeem your shares:
Strategy [Heading]	rr_StrategyHeading	Principal Investment Strategies of the Fund
Strategy Narrative [Text Block]	rr_StrategyNarrativeTextBlock	Small Cap Growth will, under normal circumstances, invest at least 80% of its net assets (plus any borrowings for investment purposes) in equity securities of small cap companies and at least 80% of its net assets (plus any borrowings for investment purposes) in securities or instruments of issuers located in the United States. Equity securities consist primarily of common stock, preferred stock, securities convertible into common stock and securities or other instruments whose price is linked to the value of common stock, such as derivatives. The Fund seeks to buy primarily common stock but also can invest in preferred stock, convertible securities and other equity securities. The Fund management team focuses on small capitalization companies that Fund management believes have above average prospects for earnings growth. Although a universal definition of small-capitalization companies does not exist, the Fund generally defines these companies as those with market capitalizations, at the time of the Fund’s investment, comparable in size to the companies in the Russell 2000® Index (between approximately $169 million and $4.1 billion as of May 31, 2014) or to the companies at the time of entry in the S&P SmallCap 600® Index (between approximately $400 million and $1.8 billion as of June 20, 2014). In the future, the Fund may define small-capitalization companies using a different index or classification system. From time to time the Fund may invest in shares of companies through “new issues” or initial public offerings (“IPOs”). The Fund may use derivatives, including options, warrants, futures, indexed securities, inverse securities, swaps and forward contracts both to seek to increase the return of the Fund and to hedge (or protect) the value of its assets against adverse movements in currency exchange rates, interest rates and movements in the securities markets. The Fund invests all of its assets in the Master Portfolio, a series of the Master LLC that has the same objective and strategies as the Fund. All investments will be made at the level of the Master Portfolio. This structure is sometimes called a “master/feeder” structure. The Fund’s investment results will correspond directly to the investment results of the underlying Master Portfolio in which it invests. For simplicity, this prospectus uses the terms “Fund” and “Small Cap Growth” to include the Master Portfolio.
Risk [Heading]	rr_RiskHeading	Principal Risks of Investing in the Fund
Risk Narrative [Text Block]	rr_RiskNarrativeTextBlock	Risk is inherent in all investing. The value of your investment in Small Cap Growth, as well as the amount of return you receive on your investment, may fluctuate significantly from day to day and over time. You may lose part or all of your investment in the Fund or your investment may not perform as well as other similar investments. The following is a summary description of principal risks of investing in the Fund. Convertible Securities Risk — The market value of a convertible security performs like that of a regular debt security; that is, if market interest rates rise, the value of a convertible security usually falls. In addition, convertible securities are subject to the risk that the issuer will not be able to pay interest or dividends when due, and their market value may change based on changes in the issuer’s credit rating or the market’s perception of the issuer’s creditworthiness. Since it derives a portion of its value from the common stock into which it may be converted, a convertible security is also subject to the same types of market and issuer risks that apply to the underlying common stock. Derivatives Risk — The Fund’s use of derivatives may reduce the Fund’s returns and/or increase volatility. Volatility is defined as the characteristic of a security, an index or a market to fluctuate significantly in price within a short time period. A risk of the Fund’s use of derivatives is that the fluctuations in their values may not correlate perfectly with the overall securities markets. Derivatives are also subject to counterparty risk, which is the risk that the other party in the transaction will not fulfill its contractual obligation. The possible lack of a liquid secondary market for derivatives and the resulting inability of the Fund to sell or otherwise close a derivatives position could expose the Fund to losses and could make derivatives more difficult for the Fund to value accurately. Valuation may be more difficult in times of market turmoil since many investors and market makers may be reluctant to purchase complex instruments or quote prices for them. Derivatives also may expose the Fund to greater risk and increase its costs. Certain transactions in derivatives involve substantial leverage risk and may expose the Fund to potential losses that exceed the amount originally invested by the Fund. The U.S. Government is in the process of adopting and implementing regulations governing derivatives markets, including mandatory clearing of certain derivatives, margin, reporting and registration requirements. The ultimate impact of the regulations remains unclear. Additional U.S. or other regulations may make derivatives more costly, may limit the availability of derivatives, or may otherwise adversely affect the value or performance of derivatives. Certain aspects of the tax treatment of derivative instruments, including swap agreements and commodity-linked derivative instruments, are currently unclear and may be affected by changes in legislation, regulations or other legally binding authority that could affect the character, timing and amount of the Fund’s taxable income or gains and distributions. Equity Securities Risk — Stock markets are volatile. The price of an equity security fluctuates based on changes in a company’s financial condition and overall market and economic conditions. High Portfolio Turnover Risk — The Fund may engage in active and frequent trading of its portfolio securities. High portfolio turnover (more than 100%) may result in increased transaction costs to the Fund, including brokerage commissions, dealer mark-ups and other transaction costs on the sale of the securities and on reinvestment in other securities. The sale of Fund portfolio securities may result in the realization and distribution to shareholders of higher capital gains or losses as compared to a fund with less active trading policies. Given the frequency of sales, such gain or loss will likely be short-term capital gain or loss and would increase an investor’s tax liability unless shares are held through a tax-deferred or tax-exempt vehicle. These effects of higher than normal portfolio turnover may adversely affect Fund performance. Investment Style Risk — Under certain market conditions, growth investments have performed better during the later stages of economic expansion. Therefore, this investment style may over time go in and out of favor. At times when the investment style used by the Fund is out of favor, the Fund may underperform other equity funds that use different investment styles. Leverage Risk — Some transactions may give rise to a form of economic leverage. These transactions may include, among others, derivatives, and may expose the Fund to greater risk and increase its costs. The use of leverage may cause the Fund to liquidate portfolio positions when it may not be advantageous to do so to satisfy its obligations or to meet any required asset segregation requirements. Increases and decreases in the value of the Fund’s portfolio will be magnified when the Fund uses leverage. Market Risk and Selection Risk — Market risk is the risk that one or more markets in which the Fund invests will go down in value, including the possibility that the markets will go down sharply and unpredictably. Selection risk is the risk that the securities selected by Fund management will underperform the markets, the relevant indices or the securities selected by other funds with similar investment objectives and investment strategies. This means you may lose money. “New Issues” Risk — “New issues” are IPOs of equity securities. Securities issued in IPOs have no trading history, and information about the companies may be available for very limited periods. In addition, the prices of securities sold in IPOs may be highly volatile or may decline shortly after the initial public offering. Small Cap and Emerging Growth Securities Risk — Small cap or emerging growth companies may have limited product lines or markets. They may be less financially secure than larger, more established companies. They may depend on a more limited management group than larger capitalized companies.
Risk Lose Money [Text]	rr_RiskLoseMoney	You may lose part or all of your investment in the Fund or your investment may not perform as well as other similar investments.
Bar Chart and Performance Table [Heading]	rr_BarChartAndPerformanceTableHeading	Performance Information
Performance Narrative [Text Block]	rr_PerformanceNarrativeTextBlock	The information shows you how the Fund’s performance has varied year by year and provides some indication of the risks of investing in the Fund. The table compares the Fund’s performance to that of the Russell 2000® Growth Index. As with all such investments, past performance (before and after taxes) is not an indication of future results. The information for the Fund in the chart and the table assumes reinvestment of dividends and distributions. The table includes all applicable fees and sales charges. Sales charges are not reflected in the bar chart. If they were, returns would be less than those shown. If BlackRock and its affiliates had not waived or reimbursed certain Fund expenses during the periods shown, the Fund’s returns would have been lower. Updated information can be obtained by visiting www.blackrock.com/funds or can be obtained by phone at (800) 882-0052.
Performance Information Illustrates Variability of Returns [Text]	rr_PerformanceInformationIllustratesVariabilityOfReturns	The information shows you how the Fund’s performance has varied year by year and provides some indication of the risks of investing in the Fund.
Performance Availability Phone [Text]	rr_PerformanceAvailabilityPhone	(800) 882-0052
Performance Availability Website Address [Text]	rr_PerformanceAvailabilityWebSiteAddress	www.blackrock.com/funds
Performance Past Does Not Indicate Future [Text]	rr_PerformancePastDoesNotIndicateFuture	As with all such investments, past performance (before and after taxes) is not an indication of future results.
Bar Chart [Heading]	rr_BarChartHeading	Investor A Shares ANNUAL TOTAL RETURNS BlackRock Small Cap Growth Fund II As of 12/31
Bar Chart Does Not Reflect Sales Loads [Text]	rr_BarChartDoesNotReflectSalesLoads	Sales charges are not reflected in the bar chart. If they were, returns would be less than those shown.
Bar Chart Closing [Text Block]	rr_BarChartClosingTextBlock	During the ten-year period shown in the bar chart, the highest return for a quarter was 26.51% (quarter ended June 30, 2009) and the lowest return for a quarter was -29.25% (quarter ended December 31, 2008). The year-to-date return as of June 30, 2014 was 2.29%.
Performance Table Heading	rr_PerformanceTableHeading	As of 12/31/13 Average Annual Total Returns
Performance Table Does Reflect Sales Loads	rr_PerformanceTableDoesReflectSalesLoads	The table includes all applicable fees and sales charges.
Performance Table Uses Highest Federal Rate	rr_PerformanceTableUsesHighestFederalRate	After-tax returns 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	Actual after-tax returns depend on the investor’s tax situation and may differ from those shown, and the after-tax returns shown are not relevant to investors who hold their shares through tax-deferred arrangements, such as 401(k) plans or individual retirement accounts.
Performance Table One Class of after Tax Shown [Text]	rr_PerformanceTableOneClassOfAfterTaxShown	After-tax returns are shown for Investor A Shares only, and the after-tax returns for Investor B, Investor C, Institutional and Class R Shares will vary.
Performance Table Narrative	rr_PerformanceTableNarrativeTextBlock	After-tax returns 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 the investor’s tax situation and may differ from those shown, and the after-tax returns shown are not relevant to investors who hold their shares through tax-deferred arrangements, such as 401(k) plans or individual retirement accounts. After-tax returns are shown for Investor A Shares only, and the after-tax returns for Investor B, Investor C, Institutional and Class R Shares will vary.
BlackRock Small Cap Growth Fund II | Investor A Shares
Risk/Return:	rr_RiskReturnAbstract
Maximum Sales Charge (Load) Imposed on Purchases (as a percentage of offering price)	rr_MaximumSalesChargeImposedOnPurchasesOverOfferingPrice	5.25%
Maximum Deferred Sales Charge (Load) (as a percentage of original purchase price or redemption proceeds, whichever is lower)	rr_MaximumDeferredSalesChargeOverOfferingPrice	none	[1]
Management Fee	rr_ManagementFeesOverAssets	0.70%	[2]
Distribution and/or Service (12b-1) Fees	rr_DistributionAndService12b1FeesOverAssets	0.25%	[2]
Administration Fee	rr_Component1OtherExpensesOverAssets	0.20%	[2]
Miscellaneous Other Expenses	rr_Component2OtherExpensesOverAssets	0.63%	[2]
Other Expenses	rr_OtherExpensesOverAssets	0.83%	[2]
Total Annual Fund Operating Expenses	rr_ExpensesOverAssets	1.78%	[2]
Fee Waivers and Expense Reimbursements	rr_FeeWaiverOrReimbursementOverAssets	(0.16%)	[2]
Total Annual Fund Operating Expenses After Fee Waivers and/or Expense Reimbursements	rr_NetExpensesOverAssets	1.62%	[2]
1 Year	rr_ExpenseExampleYear01	681
3 Years	rr_ExpenseExampleYear03	1,041
5 Years	rr_ExpenseExampleYear05	1,425
10 Years	rr_ExpenseExampleYear10	2,497
2004	rr_AnnualReturn2004	14.85%
2005	rr_AnnualReturn2005	12.93%
2006	rr_AnnualReturn2006	10.35%
2007	rr_AnnualReturn2007	14.05%
2008	rr_AnnualReturn2008	(41.08%)
2009	rr_AnnualReturn2009	34.13%
2010	rr_AnnualReturn2010	21.95%
2011	rr_AnnualReturn2011	(0.89%)
2012	rr_AnnualReturn2012	9.47%
2013	rr_AnnualReturn2013	44.83%
Year to Date Return, Label	rr_YearToDateReturnLabel	year-to-date return
Bar Chart, Year to Date Return, Date	rr_BarChartYearToDateReturnDate	Jun. 30, 2014
Bar Chart, Year to Date Return	rr_BarChartYearToDateReturn	2.29%
Highest Quarterly Return, Label	rr_HighestQuarterlyReturnLabel	highest return
Highest Quarterly Return, Date	rr_BarChartHighestQuarterlyReturnDate	Jun. 30, 2009
Highest Quarterly Return	rr_BarChartHighestQuarterlyReturn	26.51%
Lowest Quarterly Return, Label	rr_LowestQuarterlyReturnLabel	lowest return
Lowest Quarterly Return, Date	rr_BarChartLowestQuarterlyReturnDate	Dec. 31, 2008
Lowest Quarterly Return	rr_BarChartLowestQuarterlyReturn	(29.25%)
1 Year	rr_AverageAnnualReturnYear01	37.23%
5 Years	rr_AverageAnnualReturnYear05	19.49%
10 Years	rr_AverageAnnualReturnYear10	8.89%
BlackRock Small Cap Growth Fund II | Investor B Shares
Risk/Return:	rr_RiskReturnAbstract
Maximum Sales Charge (Load) Imposed on Purchases (as a percentage of offering price)	rr_MaximumSalesChargeImposedOnPurchasesOverOfferingPrice	none
Maximum Deferred Sales Charge (Load) (as a percentage of original purchase price or redemption proceeds, whichever is lower)	rr_MaximumDeferredSalesChargeOverOfferingPrice	4.50%	[3]
Management Fee	rr_ManagementFeesOverAssets	0.70%	[2]
Distribution and/or Service (12b-1) Fees	rr_DistributionAndService12b1FeesOverAssets	1.00%	[2]
Administration Fee	rr_Component1OtherExpensesOverAssets	0.20%	[2]
Miscellaneous Other Expenses	rr_Component2OtherExpensesOverAssets	0.66%	[2]
Other Expenses	rr_OtherExpensesOverAssets	0.86%	[2]
Total Annual Fund Operating Expenses	rr_ExpensesOverAssets	2.56%	[2]
Fee Waivers and Expense Reimbursements	rr_FeeWaiverOrReimbursementOverAssets	(0.16%)	[2]
Total Annual Fund Operating Expenses After Fee Waivers and/or Expense Reimbursements	rr_NetExpensesOverAssets	2.40%	[2]
1 Year	rr_ExpenseExampleYear01	693
3 Years	rr_ExpenseExampleYear03	1,131
5 Years	rr_ExpenseExampleYear05	1,546
10 Years	rr_ExpenseExampleYear10	2,692
1 Year	rr_ExpenseExampleNoRedemptionYear01	243
3 Years	rr_ExpenseExampleNoRedemptionYear03	781
5 Years	rr_ExpenseExampleNoRedemptionYear05	1,346
10 Years	rr_ExpenseExampleNoRedemptionYear10	2,692
1 Year	rr_AverageAnnualReturnYear01	38.76%
5 Years	rr_AverageAnnualReturnYear05	19.16%
10 Years	rr_AverageAnnualReturnYear10	8.58%
BlackRock Small Cap Growth Fund II | Investor C Shares
Risk/Return:	rr_RiskReturnAbstract
Maximum Sales Charge (Load) Imposed on Purchases (as a percentage of offering price)	rr_MaximumSalesChargeImposedOnPurchasesOverOfferingPrice	none
Maximum Deferred Sales Charge (Load) (as a percentage of original purchase price or redemption proceeds, whichever is lower)	rr_MaximumDeferredSalesChargeOverOfferingPrice	1.00%	[4]
Management Fee	rr_ManagementFeesOverAssets	0.70%	[2]
Distribution and/or Service (12b-1) Fees	rr_DistributionAndService12b1FeesOverAssets	1.00%	[2]
Administration Fee	rr_Component1OtherExpensesOverAssets	0.20%	[2]
Miscellaneous Other Expenses	rr_Component2OtherExpensesOverAssets	0.56%	[2]
Other Expenses	rr_OtherExpensesOverAssets	0.76%	[2]
Total Annual Fund Operating Expenses	rr_ExpensesOverAssets	2.46%	[2]
Fee Waivers and Expense Reimbursements	rr_FeeWaiverOrReimbursementOverAssets	(0.16%)	[2]
Total Annual Fund Operating Expenses After Fee Waivers and/or Expense Reimbursements	rr_NetExpensesOverAssets	2.30%	[2]
1 Year	rr_ExpenseExampleYear01	333
3 Years	rr_ExpenseExampleYear03	751
5 Years	rr_ExpenseExampleYear05	1,296
10 Years	rr_ExpenseExampleYear10	2,784
1 Year	rr_ExpenseExampleNoRedemptionYear01	233
3 Years	rr_ExpenseExampleNoRedemptionYear03	751
5 Years	rr_ExpenseExampleNoRedemptionYear05	1,296
10 Years	rr_ExpenseExampleNoRedemptionYear10	2,784
1 Year	rr_AverageAnnualReturnYear01	42.61%
5 Years	rr_AverageAnnualReturnYear05	19.63%
10 Years	rr_AverageAnnualReturnYear10	8.48%
BlackRock Small Cap Growth Fund II | Institutional Shares
Risk/Return:	rr_RiskReturnAbstract
Maximum Sales Charge (Load) Imposed on Purchases (as a percentage of offering price)	rr_MaximumSalesChargeImposedOnPurchasesOverOfferingPrice	none
Maximum Deferred Sales Charge (Load) (as a percentage of original purchase price or redemption proceeds, whichever is lower)	rr_MaximumDeferredSalesChargeOverOfferingPrice	none
Management Fee	rr_ManagementFeesOverAssets	0.70%	[2]
Distribution and/or Service (12b-1) Fees	rr_DistributionAndService12b1FeesOverAssets	none	[2]
Administration Fee	rr_Component1OtherExpensesOverAssets	0.20%	[2]
Miscellaneous Other Expenses	rr_Component2OtherExpensesOverAssets	0.40%	[2]
Other Expenses	rr_OtherExpensesOverAssets	0.60%	[2]
Total Annual Fund Operating Expenses	rr_ExpensesOverAssets	1.30%	[2]
Fee Waivers and Expense Reimbursements	rr_FeeWaiverOrReimbursementOverAssets	(0.16%)	[2]
Total Annual Fund Operating Expenses After Fee Waivers and/or Expense Reimbursements	rr_NetExpensesOverAssets	1.14%	[2]
1 Year	rr_ExpenseExampleYear01	116
3 Years	rr_ExpenseExampleYear03	396
5 Years	rr_ExpenseExampleYear05	698
10 Years	rr_ExpenseExampleYear10	1,554
1 Year	rr_AverageAnnualReturnYear01	45.50%
5 Years	rr_AverageAnnualReturnYear05	21.12%
10 Years	rr_AverageAnnualReturnYear10	9.78%
BlackRock Small Cap Growth Fund II | Class R Shares
Risk/Return:	rr_RiskReturnAbstract
Maximum Sales Charge (Load) Imposed on Purchases (as a percentage of offering price)	rr_MaximumSalesChargeImposedOnPurchasesOverOfferingPrice	none
Maximum Deferred Sales Charge (Load) (as a percentage of original purchase price or redemption proceeds, whichever is lower)	rr_MaximumDeferredSalesChargeOverOfferingPrice	none
Management Fee	rr_ManagementFeesOverAssets	0.70%	[2]
Distribution and/or Service (12b-1) Fees	rr_DistributionAndService12b1FeesOverAssets	0.50%	[2]
Administration Fee	rr_Component1OtherExpensesOverAssets	0.20%	[2]
Miscellaneous Other Expenses	rr_Component2OtherExpensesOverAssets	0.43%	[2]
Other Expenses	rr_OtherExpensesOverAssets	0.63%	[2]
Total Annual Fund Operating Expenses	rr_ExpensesOverAssets	1.83%	[2]
Fee Waivers and Expense Reimbursements	rr_FeeWaiverOrReimbursementOverAssets	(0.16%)	[2]
Total Annual Fund Operating Expenses After Fee Waivers and/or Expense Reimbursements	rr_NetExpensesOverAssets	1.67%	[2]
1 Year	rr_ExpenseExampleYear01	170
3 Years	rr_ExpenseExampleYear03	560
5 Years	rr_ExpenseExampleYear05	975
10 Years	rr_ExpenseExampleYear10	$ 2,135
1 Year	rr_AverageAnnualReturnYear01	44.54%
5 Years	rr_AverageAnnualReturnYear05	20.35%
10 Years	rr_AverageAnnualReturnYear10	9.11%
BlackRock Small Cap Growth Fund II | Return After Taxes on Distributions | Investor A Shares
Risk/Return:	rr_RiskReturnAbstract
1 Year	rr_AverageAnnualReturnYear01	28.04%
5 Years	rr_AverageAnnualReturnYear05	17.26%
10 Years	rr_AverageAnnualReturnYear10	7.35%
BlackRock Small Cap Growth Fund II | Return After Taxes on Distributions and Sale of Fund Shares | Investor A Shares
Risk/Return:	rr_RiskReturnAbstract
1 Year	rr_AverageAnnualReturnYear01	24.03%
5 Years	rr_AverageAnnualReturnYear05	15.41%
10 Years	rr_AverageAnnualReturnYear10	6.97%
BlackRock Small Cap Growth Fund II | Russell 2000® Growth Index (Reflects no deduction for fees, expenses or taxes)
Risk/Return:	rr_RiskReturnAbstract
1 Year	rr_AverageAnnualReturnYear01	43.30%
5 Years	rr_AverageAnnualReturnYear05	22.58%
10 Years	rr_AverageAnnualReturnYear10	9.41%

[1] A contingent deferred sales charge ("CDSC") of 1.00% is assessed on certain redemptions of Investor A Shares made within 18 months after purchase where no initial sales charge was paid at time of purchase as part of an investment of $1,000,000 or more.

[2] The fees and expenses shown in the table and the example that follows include both the expenses of the Fund and the Fund's share of the allocated expenses of BlackRock Master Small Cap Growth Portfolio (the "Master Portfolio") of BlackRock Master LLC (the "Master LLC"). Management fees are paid by the Master Portfolio. BlackRock has contractually agreed to waive 0.16% of the management fee payable by the Master Portfolio until October 1, 2015. The contractual agreement may be terminated upon 90 days' notice by a majority of the non-interested directors of the Master LLC or by a vote of a majority of the outstanding voting securities of the Master Portfolio.

[3] The CDSC is 4.50% if shares are redeemed in less than one year. The CDSC for Investor B Shares decreases for redemptions made in subsequent years. After six years there is no CDSC on Investor B Shares. (See the section "Details About the Share Classes — Investor B Shares" for the complete schedule of CDSCs.)

[4] There is no CDSC on Investor C Shares after one year.