Label	Element	Value
Risk/Return:	rr_RiskReturnAbstract
ProspectusDate	rr_ProspectusDate	Dec. 29, 2011
Jacob Small Cap Growth Fund (Prospectus Summary) | Jacob Small Cap Growth Fund
Risk/Return:	rr_RiskReturnAbstract
Risk/Return, Heading	rr_RiskReturnHeading	JACOB SMALL CAP GROWTH FUND
Investment Objective, Heading	rr_ObjectiveHeading	Investment Objective
investment Objective, Primary	rr_ObjectivePrimaryTextBlock	The Fund's investment objective is long-term growth of capital.
Expense, Heading	rr_ExpenseHeading	Fees and Expenses
Expense, Narrative	rr_ExpenseNarrativeTextBlock	This table describes the fees and expenses that you may pay if you buy and hold shares of the Fund.
Shareholder Fees, Caption	rr_ShareholderFeesCaption	Shareholder Fees (fees paid directly from your investment)
Operating Expenses, Caption	rr_OperatingExpensesCaption	Annual Fund Operating Expenses (expenses paid each year as a percentage of the value of your investment )
Portfolio Turnover, Heading	rr_PortfolioTurnoverHeading	Portfolio Turnover
Portfolio Turnover	rr_PortfolioTurnoverTextBlock	The Fund 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 Fund 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 Fund's portfolio turnover rate was 102.80% of the average value of its portfolio.
Portfolio Turnover, Rate	rr_PortfolioTurnoverRate	102.80%
Expense Example, Heading	rr_ExpenseExampleHeading	Example:
Expense Example, Narrative	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 over 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.
Expense Example, By Year, Caption	rr_ExpenseExampleByYearCaption	Although your actual costs may be higher or lower, based on these assumptions your costs would be:
Investment Strategy, Heading	rr_StrategyHeading	Principal Investment Strategies
Investment Strategy, Narrative	rr_StrategyNarrativeTextBlock	The Fund seeks to achieve its investment objective by investing, under normal circumstances, at least 80% of its assets in small capitalization companies. Small capitalization companies are defined as those companies with market capitalizations (share price multiplied by number of shares outstanding) within the capitalization range of the Russell 2000® Growth Index at the time of purchase. The Fund maintains a diversified portfolio of investments consisting primarily of common stocks. The Fund may also invest in other equity securities such as preferred stocks, securities convertible or exchangeable into common stocks, rights, warrants, or real estate investment trusts. The Adviser expects to select investments for the Fund in companies that are broadly diversified over various industry groups. The Adviser manages the Fund's portfolio in an aggressive growth style. The Adviser believes that investments in small capitalization companies can have greater earnings and sales growth potential than larger capitalized companies and can offer substantial opportunities for long-term growth of capital. The Adviser's overall stock selections are based on its qualitative and quantitative assessment of a company's fundamental prospects and whether it has an above-average potential for long-term growth of capital. The Adviser expects to invest the Fund's net assets primarily in U.S. companies, but may gain exposure to foreign markets through the global operations of U.S. companies, by purchasing depositary receipts or securities of foreign companies traded on U.S. exchanges, or through direct investment in foreign companies. The Adviser will not invest more than 25% of the Fund's net assets directly in foreign companies. The Fund intends to hold some cash, short-term debt obligations, government securities or other high-quality investments for reserves to cover redemptions and unanticipated expenses, or to maintain liquidity while seeking appropriate investments. There may be times, however, when the Fund attempts to respond to unfavorable market, economic, political or other conditions by investing up to 100% of its assets in cash or those types of money market investments for temporary defensive purposes. During those times, the Fund will not be able to pursue its investment objective and, instead, will focus on preserving your investment.
Risk, Heading	rr_RiskHeading	Principal Risks
Risk, Narrative	rr_RiskNarrativeTextBlock	Investing in a mutual fund has inherent risks, which could cause you to lose money. The principal risks of investing in the Fund, and the circumstances that could adversely affect the Fund's net asset value and total return, are listed below. o Market Risk: The value of the Fund's shares and the securities held by the Fund can each decline in value. Even when the stock market in general is rising, the stocks selected by the Adviser may decline. Prices of common stocks of even the best managed, most profitable corporations are subject to market risk, which means their stock prices can decline. In addition, swings in investor psychology or significant trading by large institutional investors can result in price fluctuations. o Smaller Capitalized Company Risk: Investments in small capitalization companies may involve greater risks, as these companies tend to have limited product lines, markets and financial or managerial resources. Small cap stocks often also have a more limited trading market, such that the Adviser may not be able to sell stocks at an optimal time or price. In addition, less frequently-traded securities may be subject to more abrupt price movements than securities of larger capitalized companies. o Foreign and Emerging Market Risk: The risks of investing in foreign companies, including those located in emerging market countries, can increase the potential for losses in the Fund and may include currency fluctuations, political and economic instability, less government regulation, less publicly available information, limited trading markets, differences in financial reporting standards and less stringent regulation of securities markets. Foreign securities markets generally have less volume than U.S. securities exchanges and securities of some foreign companies are less liquid and more volatile than securities of comparable U.S. companies. Additional risks include future political and economic developments, the possibility that a foreign jurisdiction might impose or increase withholding taxes on income payable with respect to foreign securities, the possible seizure, nationalization or expropriation of the foreign issuer or foreign deposits (in which the Fund could lose its entire investment in a certain market) and the possible adoption of foreign governmental restrictions such as exchange controls. o Real Estate Investment Trust Risk: Investments in real estate related instruments may be affected by economic, legal, cultural, environmental or technological factors that affect property values, rents or occupancies of real estate related to the Fund's holdings. The performance of REITs depends on how well the REIT manages the properties it owns. o Convertible Securities Risk: The market value of convertible securities tends to decline as interest rates increase and, conversely, to increase as interest rates decline. In addition, convertible securities generally offer lower interest or dividend yields than non-convertible securities of similar quality.
Risk, Lose Money	rr_RiskLoseMoney	Investing in a mutual fund has inherent risks, which could cause you to lose money.
Bar Chart and Performance Table, Heading	rr_BarChartAndPerformanceTableHeading	Performance Information
Performance, Narrative	rr_PerformanceNarrativeTextBlock	Please note that the Fund intends to file an amended Prospectus dated January 3, 2012 containing 2011 performance information. Performance information gives some indication of the risks of an investment in the Fund by comparing the Fund's performance with a broad measure of market performance. Performance information is not available because the Adviser has not managed the Fund for a full calendar year as of the date of this prospectus. In the future, the Fund will disclose performance information in a bar chart and performance table.
Performance, One Year or Less	rr_PerformanceOneYearOrLess	Performance information is not available because the Adviser has not managed the Fund for a full calendar year as of the date of this prospectus.
Jacob Small Cap Growth Fund (Prospectus Summary) | Jacob Small Cap Growth Fund | Investor Class
Risk/Return:	rr_RiskReturnAbstract
Fee Waiver or Reimbursement over Assets, Date of Termination	rr_FeeWaiverOrReimbursementOverAssetsDateOfTermination	2013-01-02
Jacob Small Cap Growth Fund | Investor Class
Risk/Return:	rr_RiskReturnAbstract
Maximum Sales Charge (Load) Imposed on Purchases	rr_MaximumSalesChargeImposedOnPurchasesOverOfferingPrice	none
Maximum Deferred Sales Charge (Load)	rr_MaximumDeferredSalesChargeOverOfferingPrice	none
Maximum Sales Charge (Load) Imposed on Reinvested Dividends	rr_MaximumSalesChargeOnReinvestedDividendsAndDistributionsOverOther	none
Redemption Fee (as a percentage of amount redeemed or exchanged within 30 days of purchase)	rr_RedemptionFeeOverRedemption	(2.00%)
Advisory Fees	rr_ManagementFeesOverAssets	0.90%
Distribution and/or Service (12b-1) Fees	rr_DistributionAndService12b1FeesOverAssets	0.35%
Other Expenses	rr_OtherExpensesOverAssets	3.20%
Total Annual Fund Operating Expenses	rr_ExpensesOverAssets	4.45%
Fee Waiver	rr_FeeWaiverOrReimbursementOverAssets	(0.90%)	[1]
Total Annual Fund Operating Expenses After Fee Waiver	rr_NetExpensesOverAssets	3.55%
Expense Example, With Redemption, 1 Year	rr_ExpenseExampleYear01	358
Expense Example, With Redemption, 3 Years	rr_ExpenseExampleYear03	1,265
Expense Example, With Redemption, 5 Years	rr_ExpenseExampleYear05	2,183
Expense Example, With Redemption, 10 Years	rr_ExpenseExampleYear10	4,523

[1] Jacob Asset Management of New York LLC, the Fund's investment adviser (the "Adviser"), has contractually agreed, through January 2, 2013, to waive up to 100% of its advisory fees to the extent that the Total Annual Fund Operating Expenses (excluding any taxes, interest, brokerage fees, acquired fund expenses and non-routine expenses) would exceed 2.45% of average daily net assets. Pursuant to this fee waiver agreement, the Adviser is entitled to recoup any fees that it waived for a period of three years following such fee waivers to the extent that such recoupment will not cause the Fund's expenses to exceed 2.45%. Please note that the maximum waiver is 0.90%, which means that the Fund's overall expenses could exceed 2.45%, as is the case above. This waiver agreement may only be terminated by the Board.