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Jacob Internet Fund  
Prospectus [Line Items] rr_ProspectusLineItems  
Risk/Return [Heading] rr_RiskReturnHeading JACOB INTERNET FUND
Objective [Heading] rr_ObjectiveHeading Investment Objectives
Objective, Primary [Text Block] rr_ObjectivePrimaryTextBlock The Fund’s primary investment objective is long-term growth of capital.
Objective, Secondary [Text Block] rr_ObjectiveSecondaryTextBlock Current income is a secondary objective.
Expense [Heading] rr_ExpenseHeading Fees and Expenses
Expense Narrative [Text Block] rr_ExpenseNarrativeTextBlock This table describes the fees and expenses that you may pay if you buy, hold, and sell shares of the Fund. You may pay other fees, such as brokerage commissions and other fees to financial intermediaries, which are not reflected in the table and the Example below.
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 paid each year as a percentage of the value of your investment)
Fee Waiver or Reimbursement over Assets, Date of Termination rr_FeeWaiverOrReimbursementOverAssetsDateOfTermination January 2, 2022
Portfolio Turnover [Heading] rr_PortfolioTurnoverHeading Portfolio Turnover
Portfolio Turnover [Text Block] 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 52% of the average value of its portfolio.
Portfolio Turnover, Rate rr_PortfolioTurnoverRate 52.00%
Expense Exchange Traded Fund Commissions [Text] rr_ExpenseExchangeTradedFundCommissions You may pay other fees, such as brokerage commissions and other fees to financial intermediaries, which are not reflected in the table and the Example below.
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 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. The Example reflects the effect of the 12b-1 fee reduction for the 1 Year example and for the first year of the 3, 5 and 10 Year examples only.
Expense Example by, Year, Caption [Text] rr_ExpenseExampleByYearCaption 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 Fund seeks to achieve its investment objectives by investing, under normal circumstances, at least 80% of its assets in securities of companies in Internet and Internet-related industries. The Fund primarily invests in common stocks and securities convertible into common stocks, but may invest up to 35% in fixed income or debt securities. The Fund may invest without limitation in foreign securities, including securities of emerging market countries (i.e., those that are in the early stages of their industrial cycles), so that the Fund has the flexibility to take full advantage of investment opportunities in Internet companies and companies in Internet-related industries. The Adviser currently does not expect to invest more than 50% of the Fund’s net assets in foreign companies. The Adviser selects investments in companies that derive a substantial portion of their revenue from Internet businesses and businesses in Internet-related industries or those that are aggressively developing and expanding their Internet and Internet-related business operations. Such investments generally will be selected from companies in the following groups: media, e-commerce, computer software, internet service providers, internet portals, wireless/broadband access, and telecommunications.
The Fund invests in companies that emphasize research and development with respect to proprietary products and services for Internet users and businesses, because the Adviser believes that these stocks have the greatest potential to rise in value. Many Internet companies are newer and have small to medium market capitalizations. The Adviser’s overall process of stock selection for the Fund is not based on the capitalization of or size of the company but rather on an assessment of the company’s fundamental prospects. The Fund generally seeks to purchase securities as long-term investments, but when circumstances warrant, securities may be sold without regard to the length of time they have been held to reduce risk or volatility or to respond to changing fundamental information.
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, to seek income, or to maintain liquidity while seeking appropriate investments.
Risk [Heading] rr_RiskHeading Principal Risks
Risk Narrative [Text Block] 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 (“NAV”) and total return, are listed below.
•Common Stock Risk: Common stock represents an ownership interest in a company. Holders of common stock are generally subject to greater risk than holders of preferred stocks and debt securities because common stockholders generally have inferior rights to receive payments from issuers in comparison with the rights of preferred stockholders, bondholders, and other creditors. Furthermore. common stocks are susceptible to general stock market fluctuations and to volatile increases and decreases in value as market confidence in, and perceptions of, their issuers change.
•Market Risk: The value of the securities in which the Fund invests may be adversely affected by fluctuations in the financial markets, regardless of how well the companies in which the Fund invests perform. The market as a whole may not favor the types of investments the Fund makes. Also, there is the risk that the price(s) of one or more of the securities or other instruments in the Fund’s portfolio will fall, or will fail to rise. Many factors can adversely affect a security’s performance, including both general financial market conditions and factors related to a specific company, government, industry, country, or geographic region. Extraordinary events, including extreme economic or political conditions, natural disasters, epidemics and pandemics, and other factors can lead to volatility in local, regional, or global markets, which can result in market losses that may be substantial. The impact of one of these types of events may be more pronounced in certain regions, sectors, industries, or asset classes in which the Fund invests, or it may be pervasive across the global financial markets. The timing and occurrence of future market disruptions cannot be predicted, nor can the
impact that government interventions, if any, adopted in response to such disruptions may have on the investment strategies of the Fund or the markets in which the Fund invests.

•Recent Market Events Risk: U.S. and international markets have experienced a significant period of volatility in recent months and years due to a number of economic, political and global macro factors, including the impact of the coronavirus (COVID-19) as a global pandemic, which has resulted in public health issues, business interruptions, growth concerns in the U.S. and overseas, layoffs, rising unemployment claims, changed travel and social behaviors and reduced consumer spending. The effects of COVID-19 may lead to a substantial economic downturn or recession in the U.S. and global economies, the recovery from which is uncertain and may last for an extended period of time.
•    Internet and Internet-Related Industries Risk: The Fund invests a significant portion of its assets in Internet and Internet-related industries and thus the value of the Fund’s shares may be susceptible to factors affecting such industries, including factors affecting the computer/Internet technology area generally, and may be susceptible to greater risk and market fluctuation than an investment in a fund that invests in a broader range of portfolio securities not concentrated in any particular area or industry. Companies in Internet and Internet-related industries face special risks associated with the rapidly changing field of computer/Internet technology. For example, their products or services may not prove commercially successful or may become obsolete quickly. The computer/Internet technology area may be subject to greater governmental regulation than many other areas and changes in governmental policies and the need for regulatory approvals may have a material adverse effect on these areas. Additionally, companies in these areas may be subject to risks of developing technologies, competitive pressures and other factors and are dependent upon consumer and business acceptance as new technologies evolve. Many Internet and Internet-related companies incur large losses in the hope of capturing market share and generating future revenues, but may never be profitable.
•    Smaller Capitalized or Unseasoned Company Risk:  The Adviser believes that smaller capitalized or unseasoned companies generally have greater earnings and sales growth potential than larger capitalized companies. However, investments in smaller capitalized or unseasoned companies may involve greater risks, in part because they have limited product lines, markets and financial or managerial resources. In addition, less frequently-traded securities may be subject to more abrupt price movements than securities of larger capitalized companies.
•    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.
•    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.
•    Fixed Income Risk: Yields and principal values of fixed income securities (bonds) will fluctuate. Generally, values of fixed income securities change inversely with interest rates. As interest rates go up, the value of debt securities tends to go down. As a result, to the extent the Fund holds fixed income investments, the value of the Fund may go down.
Risk Lose Money [Text] 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 [Text Block] rr_PerformanceNarrativeTextBlock The performance information that follows gives some indication of the risks of investing in the Fund. The bar chart shows the Fund’s performance from year to year, and the table compares the Fund’s average annual returns with those of a broad measure of market performance and an index of Internet stocks. Please note that the Fund’s past performance (before and after taxes) is not necessarily an indication of how the Fund will perform in the future. Updated performance information is available on the Fund's website at www.jacobmutualfunds.com.
Performance Information Illustrates Variability of Returns [Text] rr_PerformanceInformationIllustratesVariabilityOfReturns The performance information that follows gives some indication of the risks of investing in the Fund.
Performance Availability Website Address [Text] rr_PerformanceAvailabilityWebSiteAddress www.jacobmutualfunds.com
Performance Past Does Not Indicate Future [Text] rr_PerformancePastDoesNotIndicateFuture Please note that the Fund’s past performance (before and after taxes) is not necessarily an indication of how the Fund will perform in the future.
Bar Chart [Heading] rr_BarChartHeading Annual Total Returns through December 31, 2019 (Investor Class)
Bar Chart Closing [Text Block] rr_BarChartClosingTextBlock
Best Quarter
Q3 2010
21.20%
Worst Quarter
Q3 2011
-16.67%
Highest Quarterly Return, Label rr_HighestQuarterlyReturnLabel Best Quarter
Highest Quarterly Return, Date rr_BarChartHighestQuarterlyReturnDate Sep. 30, 2010
Highest Quarterly Return rr_BarChartHighestQuarterlyReturn 21.20%
Lowest Quarterly Return, Label rr_LowestQuarterlyReturnLabel Worst Quarter
Lowest Quarterly Return, Date rr_BarChartLowestQuarterlyReturnDate Sep. 30, 2011
Lowest Quarterly Return rr_BarChartLowestQuarterlyReturn (16.67%)
Performance Table Heading rr_PerformanceTableHeading Average Annual Total Returns through December 31, 2019
Performance Table Market Index Changed rr_PerformanceTableMarketIndexChanged The NASDAQ Internet Index replaced the Bloomberg U.S. Internet Index, which was discontinued effective September 2017.
Index No Deduction for Fees, Expenses, Taxes [Text] rr_IndexNoDeductionForFeesExpensesTaxes (reflects no deduction for fees, expenses or taxes)
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 an investor’s tax situation and may differ from those shown. After-tax returns shown are not relevant to investors who hold their Fund shares through tax-advantaged arrangements such as 401(k) plans or individual retirement accounts.
Performance Table Explanation after Tax Higher rr_PerformanceTableExplanationAfterTaxHigher The return after taxes on distribution and sale of fund shares may be higher than the return before taxes because the method of calculation assumes generally that you can use the short-term capital loss realized upon the sale of fund shares to offset income of the same tax character from other sources thereby reducing the amount of tax you otherwise might owe.
Performance Table Closing [Text Block] rr_PerformanceTableClosingTextBlock 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 an investor’s tax situation and may differ from those shown. After-tax returns shown are not relevant to investors who hold their Fund shares through tax-advantaged arrangements such as 401(k) plans or individual retirement accounts. The return after taxes on distribution and sale of fund shares may be higher than the return before taxes because the method of calculation assumes generally that you can use the short-term capital loss realized upon the sale of fund shares to offset income of the same tax character from other sources thereby reducing the amount of tax you otherwise might owe.
Jacob Internet Fund | S&P 500 Index (reflects no deduction for fees, expenses, or taxes)  
Prospectus [Line Items] rr_ProspectusLineItems  
Label rr_AverageAnnualReturnLabel S&P 500 Index(reflects no deduction for fees, expenses or taxes)
1 Year rr_AverageAnnualReturnYear01 31.49%
5 Years rr_AverageAnnualReturnYear05 11.70%
10 Years rr_AverageAnnualReturnYear10 13.56%
Jacob Internet Fund | NASDAQ Composite Index (reflects no deductions for fees, expenses or taxes)  
Prospectus [Line Items] rr_ProspectusLineItems  
Label rr_AverageAnnualReturnLabel NASDAQ Composite Index(reflects no deduction for fees, expenses or taxes)
1 Year rr_AverageAnnualReturnYear01 36.74%
5 Years rr_AverageAnnualReturnYear05 15.00%
10 Years rr_AverageAnnualReturnYear10 16.14%
Jacob Internet Fund | NASDAQ Internet Index (reflects no deduction for fees, expenses or taxes)  
Prospectus [Line Items] rr_ProspectusLineItems  
Label rr_AverageAnnualReturnLabel NASDAQ Internet Index*(reflects no deduction for fees, expenses or taxes) [1]
1 Year rr_AverageAnnualReturnYear01 29.72% [1]
5 Years rr_AverageAnnualReturnYear05 16.81% [1]
10 Years rr_AverageAnnualReturnYear10 19.27% [1]
Jacob Internet Fund | Investor Class  
Prospectus [Line Items] rr_ProspectusLineItems  
Trading Symbol dei_TradingSymbol JAMFX
Maximum Sales Charge Imposed on Purchases (as a percentage of Offering Price) rr_MaximumSalesChargeImposedOnPurchasesOverOfferingPrice none
Maximum Deferred Sales Charge (as a percentage of Offering Price) rr_MaximumDeferredSalesChargeOverOfferingPrice none
Redemption Fee (as a percentage of Amount Redeemed) rr_RedemptionFeeOverRedemption (2.00%)
Management Fees (as a percentage of Assets) rr_ManagementFeesOverAssets 1.25%
Distribution and Service (12b-1) Fees rr_DistributionAndService12b1FeesOverAssets 0.25% [2]
Other Expenses (as a percentage of Assets): rr_OtherExpensesOverAssets 1.00%
Expenses (as a percentage of Assets) rr_ExpensesOverAssets 2.50%
Expense Example, with Redemption, 1 Year rr_ExpenseExampleYear01 $ 253
Expense Example, with Redemption, 3 Years rr_ExpenseExampleYear03 779
Expense Example, with Redemption, 5 Years rr_ExpenseExampleYear05 1,331
Expense Example, with Redemption, 10 Years rr_ExpenseExampleYear10 $ 2,836
Annual Return 2010 rr_AnnualReturn2010 35.45%
Annual Return 2011 rr_AnnualReturn2011 (9.06%)
Annual Return 2012 rr_AnnualReturn2012 11.44%
Annual Return 2013 rr_AnnualReturn2013 40.73%
Annual Return 2014 rr_AnnualReturn2014 0.70%
Annual Return 2015 rr_AnnualReturn2015 10.98%
Annual Return 2016 rr_AnnualReturn2016 12.04%
Annual Return 2017 rr_AnnualReturn2017 24.15%
Annual Return 2018 rr_AnnualReturn2018 1.86%
Annual Return 2019 rr_AnnualReturn2019 21.69%
Label rr_AverageAnnualReturnLabel Return Before Taxes
1 Year rr_AverageAnnualReturnYear01 21.69%
5 Years rr_AverageAnnualReturnYear05 13.86%
10 Years rr_AverageAnnualReturnYear10 14.05%
Jacob Internet Fund | Investor Class | After Taxes on Distributions  
Prospectus [Line Items] rr_ProspectusLineItems  
Label rr_AverageAnnualReturnLabel Return After Taxes on Distributions
1 Year rr_AverageAnnualReturnYear01 18.36%
5 Years rr_AverageAnnualReturnYear05 11.20%
10 Years rr_AverageAnnualReturnYear10 12.43%
Jacob Internet Fund | Investor Class | After Taxes on Distributions and Sales  
Prospectus [Line Items] rr_ProspectusLineItems  
Label rr_AverageAnnualReturnLabel Return After Taxes on Distributions and Sale of Fund Shares
1 Year rr_AverageAnnualReturnYear01 15.14%
5 Years rr_AverageAnnualReturnYear05 10.56%
10 Years rr_AverageAnnualReturnYear10 11.46%
Jacob Small Cap Growth Fund  
Prospectus [Line Items] rr_ProspectusLineItems  
Risk/Return [Heading] rr_RiskReturnHeading JACOB SMALL CAP GROWTH FUND
Objective [Heading] rr_ObjectiveHeading Investment Objective
Objective, Primary [Text Block] rr_ObjectivePrimaryTextBlock The Fund’s investment objective is long-term growth of capital.
Expense [Heading] rr_ExpenseHeading Fees and Expenses
Expense Narrative [Text Block] rr_ExpenseNarrativeTextBlock This table describes the fees and expenses that you may pay if you buy, hold, and sell shares of the Fund. You may pay other fees, such as brokerage commissions and other fees to financial intermediaries, which are not reflected in the table and the Example below.
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 paid each year as a percentage of the value of your investment)
Fee Waiver or Reimbursement over Assets, Date of Termination rr_FeeWaiverOrReimbursementOverAssetsDateOfTermination January 2, 2022
Portfolio Turnover [Heading] rr_PortfolioTurnoverHeading Portfolio Turnover
Portfolio Turnover [Text Block] 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 89% of the average value of its portfolio.
Portfolio Turnover, Rate rr_PortfolioTurnoverRate 89.00%
Expense Exchange Traded Fund Commissions [Text] rr_ExpenseExchangeTradedFundCommissions You may pay other fees, such as brokerage commissions and other fees to financial intermediaries, which are not reflected in the table and the Example below.
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 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. The Example reflects the effect of the 12b-1 fee reduction (Investor Class shares only) and adjustments made to the Fund’s operating expenses due to the fee waiver by the Adviser for the 1 Year numbers and for the first year of the 3, 5, and 10 Year numbers only.
Expense Example by, Year, Caption [Text] rr_ExpenseExampleByYearCaption 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 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. As of August 31, 2020, the market capitalization of the largest company in the Russell 2000® Growth Index was approximately $7.204 billion, and the weighted average and median market capitalizations of the Russell 2000® Growth Index were approximately $2.93 billion and $962 million, respectively.
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, rights, or warrants. The Adviser expects to select investments for the Fund in companies across 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, including emerging 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.
Risk [Heading] rr_RiskHeading Principal Risks
Risk Narrative [Text Block] 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 NAV and total return, are listed below.
•Common Stock Risk: Common stock represents an ownership interest in a company. Holders of common stock are generally subject to greater risk than holders of preferred stocks and debt securities because common stockholders generally have inferior rights to receive payments from issuers in comparison with the rights of preferred stockholders, bondholders, and other creditors. Furthermore. common stocks are susceptible to general stock market fluctuations and to volatile increases and decreases in value as market confidence in, and perceptions of, their issuers change.
•    Market Risk: The value of the securities in which the Fund invests may be adversely affected by fluctuations in the financial markets, regardless of how well the companies in which the Fund invests perform. The market as a whole may not favor the types of investments the Fund makes. Also, there is the risk that the price(s) of one or more of the securities or other instruments in the Fund’s portfolio will fall, or will fail to rise. Many factors can adversely affect a security’s performance, including both general financial market conditions and factors related to a specific company, government, industry, country, or geographic region. Extraordinary events, including extreme economic or political conditions, natural disasters, epidemics and pandemics, and other factors can lead to volatility in local, regional, or global markets, which can result in market losses that may be substantial. The impact of one of these types of events may be more pronounced in certain regions, sectors, industries, or asset classes in which the Fund invests, or it may be pervasive across the global financial markets. The timing and occurrence of future market disruptions cannot be predicted, nor can the impact that government interventions, if any, adopted in response to such disruptions may have on the investment strategies of the Fund or the markets in which the Fund invests.
•Recent Market Events Risk: U.S. and international markets have experienced a significant period of volatility in recent months and years due to a number of economic, political and global macro factors, including the impact of the coronavirus (COVID-19) as a global pandemic, which has resulted in public health issues, business interruptions, growth concerns in the U.S. and overseas, layoffs, rising unemployment claims, changed travel and social behaviors and reduced consumer spending. The effects of COVID-19 may lead to a substantial economic downturn or recession in the U.S. and global economies, the recovery from which is uncertain and may last for an extended period of time.
•    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.
•    Growth Companies Risk:  Growth companies are expected to increase their earnings at a certain rate. When these expectations are not met, the prices of these stocks may go down, even if earnings showed an absolute increase. Growth company stocks also typically lack the dividend yield that can cushion stock prices in market downturns. Different investment styles tend to shift in and out of favor, depending on market conditions and investor sentiment. The Fund’s growth style may cause the Fund to underperform funds that have a broader investment style.
•    Science and Technology Risk: The Fund’s investments in science and technology companies expose the Fund to special risks. For example, rapid advances in science and technology might cause existing products to become obsolete, and the Fund’s returns could suffer to the extent it holds an affected company’s shares. Companies in a number of science and technology industries are also subject to more government regulations and approval processes than many other industries. This fact may affect a company’s overall profitability and cause its stock price to be more volatile. Additionally, science and technology companies are dependent upon consumer and business acceptance as new technologies evolve.
•    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.
Risk Lose Money [Text] 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 [Text Block] rr_PerformanceNarrativeTextBlock The performance information that follows gives some indication of the risks of investing in the Fund. The bar chart shows the Fund’s performance for the last calendar year, and the table compares the Fund’s average annual returns with those of a broad measure of market performance. Please note that the Fund’s past performance (before and after taxes) is not necessarily an indication of how the Fund will perform in the future. Updated performance information is available on the Fund's website at www.jacobmutualfunds.com.
Performance Information Illustrates Variability of Returns [Text] rr_PerformanceInformationIllustratesVariabilityOfReturns The performance information that follows gives some indication of the risks of investing in the Fund.
Performance Availability Website Address [Text] rr_PerformanceAvailabilityWebSiteAddress www.jacobmutualfunds.com
Performance Past Does Not Indicate Future [Text] rr_PerformancePastDoesNotIndicateFuture Please note that the Fund’s past performance (before and after taxes) is not necessarily an indication of how the Fund will perform in the future.
Bar Chart [Heading] rr_BarChartHeading Annual Total Returns through December 31, 2019 (Investor Class)
Bar Chart Closing [Text Block] rr_BarChartClosingTextBlock
Best Quarter
Q3 2016
21.01%
Worst Quarter
Q3 2015
-28.19%
Highest Quarterly Return, Label rr_HighestQuarterlyReturnLabel Best Quarter
Highest Quarterly Return, Date rr_BarChartHighestQuarterlyReturnDate Sep. 30, 2016
Highest Quarterly Return rr_BarChartHighestQuarterlyReturn 21.01%
Lowest Quarterly Return, Label rr_LowestQuarterlyReturnLabel Worst Quarter
Lowest Quarterly Return, Date rr_BarChartLowestQuarterlyReturnDate Sep. 30, 2015
Lowest Quarterly Return rr_BarChartLowestQuarterlyReturn (28.19%)
Performance Table Heading rr_PerformanceTableHeading Average Annual Total Returns through December 31, 2019
Index No Deduction for Fees, Expenses, Taxes [Text] rr_IndexNoDeductionForFeesExpensesTaxes (reflects no deduction for fees, expenses or taxes)
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 an investor’s tax situation and may differ from those shown. After-tax returns shown are not relevant to investors who hold their Fund shares through tax-advantaged 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 Class shares only and after-tax returns for Institutional Class shares will vary.
Performance Table Explanation after Tax Higher rr_PerformanceTableExplanationAfterTaxHigher The return after taxes on distribution and sale of fund shares may be higher than the return before taxes because the method of calculation assumes generally that you can use the short-term capital loss realized upon the sale of fund shares to offset income of the same tax character from other sources thereby reducing the amount of tax you otherwise might owe.
Performance Table Closing [Text Block] rr_PerformanceTableClosingTextBlock 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 an investor’s tax situation and may differ from those shown. After-tax returns shown are not relevant to investors who hold their Fund shares through tax-advantaged arrangements such as 401(k) plans or individual retirement accounts. The return after taxes on distribution and sale of fund shares may be higher than the return before taxes because the method of calculation assumes generally that you can use the short-term capital loss realized upon the sale of fund shares to offset income of the same tax character from other sources thereby reducing the amount of tax you otherwise might owe. After-tax returns are shown for Investor Class shares only and after-tax returns for Institutional Class shares will vary.
Jacob Small Cap Growth Fund | Russell 2000® Growth Index Investor Class Comparison (reflects no deductions for fees, expenses or taxes)  
Prospectus [Line Items] rr_ProspectusLineItems  
Label rr_AverageAnnualReturnLabel Russell 2000® Growth Index(reflects no deduction for fees, expenses or taxes)
1 Year rr_AverageAnnualReturnYear01 28.48%
5 Years rr_AverageAnnualReturnYear05 9.34%
Since Inception rr_AverageAnnualReturnSinceInception 13.51% [3]
Inception Date rr_AverageAnnualReturnInceptionDate Feb. 01, 2010
Jacob Small Cap Growth Fund | Russell 2000® Growth Index Institutional Class Comparison (reflects no deductions for fees, expenses or taxes)  
Prospectus [Line Items] rr_ProspectusLineItems  
Label rr_AverageAnnualReturnLabel Russell 2000® Growth Index(reflects no deduction for fees, expenses or taxes)
1 Year rr_AverageAnnualReturnYear01 28.48%
5 Years rr_AverageAnnualReturnYear05 9.34%
Since Inception rr_AverageAnnualReturnSinceInception 13.83%
Inception Date rr_AverageAnnualReturnInceptionDate Nov. 12, 2012
Jacob Small Cap Growth Fund | Investor Class  
Prospectus [Line Items] rr_ProspectusLineItems  
Trading Symbol dei_TradingSymbol JSCGX
Maximum Sales Charge Imposed on Purchases (as a percentage of Offering Price) rr_MaximumSalesChargeImposedOnPurchasesOverOfferingPrice none
Maximum Deferred Sales Charge (as a percentage of Offering Price) rr_MaximumDeferredSalesChargeOverOfferingPrice none
Redemption Fee (as a percentage of Amount Redeemed) rr_RedemptionFeeOverRedemption (2.00%)
Management Fees (as a percentage of Assets) rr_ManagementFeesOverAssets 0.80%
Distribution and Service (12b-1) Fees rr_DistributionAndService12b1FeesOverAssets 0.25% [4]
Other Expenses (as a percentage of Assets): rr_OtherExpensesOverAssets 1.76%
Expenses (as a percentage of Assets) rr_ExpensesOverAssets 2.81%
Fee Waiver or Reimbursement rr_FeeWaiverOrReimbursementOverAssets (0.56%) [5]
Net Expenses (as a percentage of Assets) rr_NetExpensesOverAssets 2.25%
Expense Example, with Redemption, 1 Year rr_ExpenseExampleYear01 $ 228
Expense Example, with Redemption, 3 Years rr_ExpenseExampleYear03 818
Expense Example, with Redemption, 5 Years rr_ExpenseExampleYear05 1,435
Expense Example, with Redemption, 10 Years rr_ExpenseExampleYear10 $ 3,097
Annual Return 2011 rr_AnnualReturn2011 (13.93%)
Annual Return 2012 rr_AnnualReturn2012 6.04%
Annual Return 2013 rr_AnnualReturn2013 37.75%
Annual Return 2014 rr_AnnualReturn2014 1.13%
Annual Return 2015 rr_AnnualReturn2015 (13.19%)
Annual Return 2016 rr_AnnualReturn2016 6.34%
Annual Return 2017 rr_AnnualReturn2017 20.61%
Annual Return 2018 rr_AnnualReturn2018 8.26%
Annual Return 2019 rr_AnnualReturn2019 20.00%
Label rr_AverageAnnualReturnLabel Return Before Taxes
1 Year rr_AverageAnnualReturnYear01 20.00%
5 Years rr_AverageAnnualReturnYear05 7.66%
Since Inception rr_AverageAnnualReturnSinceInception 9.97% [3]
Inception Date rr_AverageAnnualReturnInceptionDate Feb. 01, 2010
Jacob Small Cap Growth Fund | Investor Class | After Taxes on Distributions  
Prospectus [Line Items] rr_ProspectusLineItems  
Label rr_AverageAnnualReturnLabel Return After Taxes on Distributions
1 Year rr_AverageAnnualReturnYear01 19.05%
5 Years rr_AverageAnnualReturnYear05 7.36%
Since Inception rr_AverageAnnualReturnSinceInception 9.63% [3]
Jacob Small Cap Growth Fund | Investor Class | After Taxes on Distributions and Sales  
Prospectus [Line Items] rr_ProspectusLineItems  
Label rr_AverageAnnualReturnLabel Return After Taxes on Distributions and Sale of Fund Shares
1 Year rr_AverageAnnualReturnYear01 12.13%
5 Years rr_AverageAnnualReturnYear05 5.92%
Since Inception rr_AverageAnnualReturnSinceInception 8.07% [3]
Jacob Small Cap Growth Fund | Institutional Class  
Prospectus [Line Items] rr_ProspectusLineItems  
Trading Symbol dei_TradingSymbol JSIGX
Maximum Sales Charge Imposed on Purchases (as a percentage of Offering Price) rr_MaximumSalesChargeImposedOnPurchasesOverOfferingPrice none
Maximum Deferred Sales Charge (as a percentage of Offering Price) rr_MaximumDeferredSalesChargeOverOfferingPrice none
Redemption Fee (as a percentage of Amount Redeemed) rr_RedemptionFeeOverRedemption (2.00%)
Management Fees (as a percentage of Assets) rr_ManagementFeesOverAssets 0.80%
Distribution and Service (12b-1) Fees rr_DistributionAndService12b1FeesOverAssets none [4]
Other Expenses (as a percentage of Assets): rr_OtherExpensesOverAssets 1.76%
Expenses (as a percentage of Assets) rr_ExpensesOverAssets 2.56%
Fee Waiver or Reimbursement rr_FeeWaiverOrReimbursementOverAssets (0.61%) [5]
Net Expenses (as a percentage of Assets) rr_NetExpensesOverAssets 1.95%
Expense Example, with Redemption, 1 Year rr_ExpenseExampleYear01 $ 198
Expense Example, with Redemption, 3 Years rr_ExpenseExampleYear03 739
Expense Example, with Redemption, 5 Years rr_ExpenseExampleYear05 1,306
Expense Example, with Redemption, 10 Years rr_ExpenseExampleYear10 $ 2,850
Label rr_AverageAnnualReturnLabel Return Before Taxes
1 Year rr_AverageAnnualReturnYear01 20.34%
5 Years rr_AverageAnnualReturnYear05 7.95%
Since Inception rr_AverageAnnualReturnSinceInception 11.30%
Inception Date rr_AverageAnnualReturnInceptionDate Nov. 12, 2012
Jacob Micro Cap Growth Fund  
Prospectus [Line Items] rr_ProspectusLineItems  
Risk/Return [Heading] rr_RiskReturnHeading JACOB DISCOVERY FUND
Objective [Heading] rr_ObjectiveHeading Investment Objective
Objective, Primary [Text Block] rr_ObjectivePrimaryTextBlock The Fund’s investment objective is long-term growth of capital.
Expense [Heading] rr_ExpenseHeading Fees and Expenses
Expense Narrative [Text Block] rr_ExpenseNarrativeTextBlock This table describes the fees and expenses that you may pay if you buy, hold, and sell shares of the Fund. You may pay other fees, such as brokerage commissions and other fees to financial intermediaries, which are not reflected in the table and the Example below.
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 paid each year as a percentage of the value of your investment)
Fee Waiver or Reimbursement over Assets, Date of Termination rr_FeeWaiverOrReimbursementOverAssetsDateOfTermination January 2, 2022
Portfolio Turnover [Heading] rr_PortfolioTurnoverHeading Portfolio Turnover
Portfolio Turnover [Text Block] 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 83% of the average value of its portfolio.
Portfolio Turnover, Rate rr_PortfolioTurnoverRate 83.00%
Expense Exchange Traded Fund Commissions [Text] rr_ExpenseExchangeTradedFundCommissions You may pay other fees, such as brokerage commissions and other fees to financial intermediaries, which are not reflected in the table and the Example below.
Expenses Not Correlated to Ratio Due to Acquired Fund Fees [Text] rr_ExpensesNotCorrelatedToRatioDueToAcquiredFundFees Total Annual Fund Operating Expenses differs from the corresponding ratio of gross operating expenses to average net assets in the Financial Highlights section of the Prospectus because of the acquired fund fees and expenses noted above.
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 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. The Example reflects the effect of the 12b-1 fee reduction (Investor Class shares only) and adjustments made to the Fund’s operating expenses due to the fee waiver by the Adviser for the 1 Year numbers and for the first year of the 3, 5, and 10 Year numbers only.
Expense Example by, Year, Caption [Text] rr_ExpenseExampleByYearCaption 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 Fund seeks to achieve its investment objective by investing, under normal circumstances, at least 80% of its assets in micro capitalization companies. Micro capitalization companies are defined as those companies with market capitalizations (share price multiplied by number of shares outstanding) of (1) less than or equal to $600 million; or (2) within the capitalization range of the Russell Micro Cap® Growth Index at the time of purchase. As of August 31, 2020, the market capitalization of the largest company in the Russell Micro Cap® Growth Index was approximately $3.85 billion, and the weighted average and median market capitalizations of the Russell Micro Cap® Growth Index were approximately $759 million and $211 million, respectively.
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, rights, or warrants. The Adviser expects to select investments for the Fund in companies across various industry groups.
The Adviser manages the Fund’s portfolio in an aggressive growth style. The Adviser believes that investments in micro 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, including emerging 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.
Risk [Heading] rr_RiskHeading Principal Risks
Risk Narrative [Text Block] 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 NAV and total return, are listed below.
•Common Stock Risk: Common stock represents an ownership interest in a company. Holders of common stock are generally subject to greater risk than holders of preferred stocks and debt securities because common stockholders generally have inferior rights to receive payments from issuers in comparison with the rights of preferred stockholders, bondholders, and other creditors. Furthermore. common stocks are susceptible to general stock market fluctuations and to volatile increases and decreases in value as market confidence in, and perceptions of, their issuers change.
•    Market Risk: The value of the securities in which the Fund invests may be adversely affected by fluctuations in the financial markets, regardless of how well the companies in which the Fund invests perform. The market as a whole may not favor the types of investments the Fund makes. Also, there is the risk that the price(s) of one or more of the securities or other instruments in the Fund’s portfolio will fall, or will fail to rise. Many factors can adversely affect a security’s performance, including both general financial market conditions and factors related to a specific company, government, industry, country, or geographic region. Extraordinary events, including extreme economic or political conditions, natural disasters, epidemics and pandemics, and other factors can lead to volatility in local, regional, or global markets, which can result in market losses that may be substantial. The impact of one of these types of events may be more pronounced in certain regions, sectors, industries, or asset classes in which the Fund invests, or it may be pervasive across the global financial markets. The timing and occurrence of future market disruptions cannot be predicted, nor can the impact that government interventions, if any, adopted in response to such disruptions may have on the investment strategies of the Fund or the markets in which the Fund invests.
•Recent Market Events Risk: U.S. and international markets have experienced a significant period of volatility in recent months and years due to a number of economic, political and global macro factors, including the impact of the coronavirus (COVID-19) as a global pandemic, which has resulted in public health issues, business interruptions, growth concerns in the U.S. and overseas, layoffs, rising unemployment claims, changed travel and social behaviors and reduced consumer spending. The effects of COVID-19 may lead to a substantial economic downturn or recession in the U.S. and global economies, the recovery from which is uncertain and may last for an extended period of time.
•    Micro Capitalized Company Risk:  Investments in micro capitalization companies may involve greater risks, as these companies tend to have limited product lines, markets and financial or managerial resources. Micro 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.
•    Growth Companies Risk:  Growth companies are expected to increase their earnings at a certain rate. When these expectations are not met, the prices of these stocks may go down, even if earnings showed an absolute increase. Growth company stocks also typically lack the dividend yield that can cushion stock prices in market downturns. Different investment styles tend to shift in and out of favor, depending on market conditions and investor sentiment. The Fund’s growth style may cause the Fund to underperform funds that have a broader investment style.
•    Science and Technology Risk: The Fund’s investments in science and technology companies expose the Fund to special risks. For example, rapid advances in science and technology might cause existing products to become obsolete, and the Fund’s returns could suffer to the extent it holds an affected company’s shares. Companies in a number of science and technology industries are also subject to more government regulations and approval processes than many other industries. This fact may affect a company’s overall profitability and cause its stock price to be more volatile. Additionally, science and technology companies are dependent upon consumer and business acceptance as new technologies evolve.
•    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.
Risk Lose Money [Text] 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 [Text Block] rr_PerformanceNarrativeTextBlock The performance information that follows gives some indication of the risks of investing in the Fund. The bar chart shows the Fund’s performance for the last calendar year, and the table compares the Fund’s average annual returns with those of a broad measure of market performance. Please note that the Fund’s past performance (before and after taxes) is not necessarily an indication of how the Fund will perform in the future. Updated performance information is available on the Fund's website at www.jacobmutualfunds.com.
Performance Information Illustrates Variability of Returns [Text] rr_PerformanceInformationIllustratesVariabilityOfReturns The performance information that follows gives some indication of the risks of investing in the Fund.
Performance Availability Website Address [Text] rr_PerformanceAvailabilityWebSiteAddress www.jacobmutualfunds.com
Performance Past Does Not Indicate Future [Text] rr_PerformancePastDoesNotIndicateFuture Please note that the Fund’s past performance (before and after taxes) is not necessarily an indication of how the Fund will perform in the future.
Bar Chart [Heading] rr_BarChartHeading Annual Total Returns through December 31, 2019 (Investor Class)
Bar Chart Closing [Text Block] rr_BarChartClosingTextBlock
Best Quarter
Q1 2019
18.89%
Worst Quarter
Q3 2015
-22.48%
Highest Quarterly Return, Label rr_HighestQuarterlyReturnLabel Best Quarter
Highest Quarterly Return, Date rr_BarChartHighestQuarterlyReturnDate Mar. 31, 2019
Highest Quarterly Return rr_BarChartHighestQuarterlyReturn 18.89%
Lowest Quarterly Return, Label rr_LowestQuarterlyReturnLabel Worst Quarter
Lowest Quarterly Return, Date rr_BarChartLowestQuarterlyReturnDate Sep. 30, 2015
Lowest Quarterly Return rr_BarChartLowestQuarterlyReturn (22.48%)
Performance Table Heading rr_PerformanceTableHeading Average Annual Total Returns through December 31, 2019
Index No Deduction for Fees, Expenses, Taxes [Text] rr_IndexNoDeductionForFeesExpensesTaxes (reflects no deduction for fees, expenses or taxes)
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 an investor’s tax situation and may differ from those shown. After-tax returns shown are not relevant to investors who hold their Fund shares through tax-advantaged 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 Class shares only and after-tax returns for Institutional Class shares will vary.
Performance Table Explanation after Tax Higher rr_PerformanceTableExplanationAfterTaxHigher The return after taxes on distribution and sale of fund shares may be higher than the return before taxes because the method of calculation assumes generally that you can use the short-term capital loss realized upon the sale of fund shares to offset income of the same tax character from other sources thereby reducing the amount of tax you otherwise might owe.
Performance Table Closing [Text Block] rr_PerformanceTableClosingTextBlock 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 an investor’s tax situation and may differ from those shown. After-tax returns shown are not relevant to investors who hold their Fund shares through tax-advantaged arrangements such as 401(k) plans or individual retirement accounts. The return after taxes on distribution and sale of fund shares may be higher than the return before taxes because the method of calculation assumes generally that you can use the short-term capital loss realized upon the sale of fund shares to offset income of the same tax character from other sources thereby reducing the amount of tax you otherwise might owe. After-tax returns are shown for Investor Class shares only and after-tax returns for Institutional Class shares will vary.
Jacob Micro Cap Growth Fund | Russell Microcap Growth Index (reflects no deduction for fees, expenses or taxes)  
Prospectus [Line Items] rr_ProspectusLineItems  
Label rr_AverageAnnualReturnLabel Russell Microcap Growth Index(reflects no deduction for fees, expenses or taxes)
1 Year rr_AverageAnnualReturnYear01 23.33%
5 Years rr_AverageAnnualReturnYear05 4.87%
Since Inception rr_AverageAnnualReturnSinceInception 9.93% [6]
Inception Date rr_AverageAnnualReturnInceptionDate Oct. 16, 2012
Jacob Micro Cap Growth Fund | Russell 2000® Growth Index Institutional Class Comparison (reflects no deductions for fees, expenses or taxes)  
Prospectus [Line Items] rr_ProspectusLineItems  
Label rr_AverageAnnualReturnLabel Russell 2000® Growth Index(reflects no deduction for fees, expenses or taxes)
1 Year rr_AverageAnnualReturnYear01 28.48%
5 Years rr_AverageAnnualReturnYear05 9.34%
Since Inception rr_AverageAnnualReturnSinceInception 12.80% [6]
Inception Date rr_AverageAnnualReturnInceptionDate Oct. 16, 2012
Jacob Micro Cap Growth Fund | Investor Class  
Prospectus [Line Items] rr_ProspectusLineItems  
Trading Symbol dei_TradingSymbol JMCGX
Maximum Sales Charge Imposed on Purchases (as a percentage of Offering Price) rr_MaximumSalesChargeImposedOnPurchasesOverOfferingPrice none
Maximum Deferred Sales Charge (as a percentage of Offering Price) rr_MaximumDeferredSalesChargeOverOfferingPrice none
Redemption Fee (as a percentage of Amount Redeemed) rr_RedemptionFeeOverRedemption (2.00%)
Management Fees (as a percentage of Assets) rr_ManagementFeesOverAssets 1.10%
Distribution and Service (12b-1) Fees rr_DistributionAndService12b1FeesOverAssets 0.25% [7]
Other Expenses (as a percentage of Assets): rr_OtherExpensesOverAssets 1.80%
Acquired Fund Fees and Expenses rr_AcquiredFundFeesAndExpensesOverAssets 0.01%
Expenses (as a percentage of Assets) rr_ExpensesOverAssets 3.16% [8]
Fee Waiver or Reimbursement rr_FeeWaiverOrReimbursementOverAssets (0.85%) [9]
Net Expenses (as a percentage of Assets) rr_NetExpensesOverAssets 2.31% [8]
Expense Example, with Redemption, 1 Year rr_ExpenseExampleYear01 $ 233
Expense Example, with Redemption, 3 Years rr_ExpenseExampleYear03 892
Expense Example, with Redemption, 5 Years rr_ExpenseExampleYear05 1,576
Expense Example, with Redemption, 10 Years rr_ExpenseExampleYear10 $ 3,399
Annual Return 2013 rr_AnnualReturn2013 37.08%
Annual Return 2014 rr_AnnualReturn2014 (4.77%)
Annual Return 2015 rr_AnnualReturn2015 (9.02%)
Annual Return 2016 rr_AnnualReturn2016 (10.69%)
Annual Return 2017 rr_AnnualReturn2017 28.66%
Annual Return 2018 rr_AnnualReturn2018 10.34%
Annual Return 2019 rr_AnnualReturn2019 42.47%
Label rr_AverageAnnualReturnLabel Return Before Taxes
1 Year rr_AverageAnnualReturnYear01 42.47%
5 Years rr_AverageAnnualReturnYear05 10.44%
Since Inception rr_AverageAnnualReturnSinceInception 10.55% [6]
Inception Date rr_AverageAnnualReturnInceptionDate Oct. 16, 2012
Jacob Micro Cap Growth Fund | Investor Class | After Taxes on Distributions  
Prospectus [Line Items] rr_ProspectusLineItems  
Label rr_AverageAnnualReturnLabel Return After Taxes on Distributions
1 Year rr_AverageAnnualReturnYear01 42.47%
5 Years rr_AverageAnnualReturnYear05 8.74%
Since Inception rr_AverageAnnualReturnSinceInception 7.45% [6]
Jacob Micro Cap Growth Fund | Investor Class | After Taxes on Distributions and Sales  
Prospectus [Line Items] rr_ProspectusLineItems  
Label rr_AverageAnnualReturnLabel Return After Taxes on Distributions and Sale of Fund Shares
1 Year rr_AverageAnnualReturnYear01 25.14%
5 Years rr_AverageAnnualReturnYear05 7.42%
Since Inception rr_AverageAnnualReturnSinceInception 7.06% [6]
Jacob Micro Cap Growth Fund | Institutional Class  
Prospectus [Line Items] rr_ProspectusLineItems  
Trading Symbol dei_TradingSymbol JMIGX
Maximum Sales Charge Imposed on Purchases (as a percentage of Offering Price) rr_MaximumSalesChargeImposedOnPurchasesOverOfferingPrice none
Maximum Deferred Sales Charge (as a percentage of Offering Price) rr_MaximumDeferredSalesChargeOverOfferingPrice none
Redemption Fee (as a percentage of Amount Redeemed) rr_RedemptionFeeOverRedemption (2.00%)
Management Fees (as a percentage of Assets) rr_ManagementFeesOverAssets 1.10%
Distribution and Service (12b-1) Fees rr_DistributionAndService12b1FeesOverAssets none [7]
Other Expenses (as a percentage of Assets): rr_OtherExpensesOverAssets 1.80%
Acquired Fund Fees and Expenses rr_AcquiredFundFeesAndExpensesOverAssets 0.01%
Expenses (as a percentage of Assets) rr_ExpensesOverAssets 2.91% [8]
Fee Waiver or Reimbursement rr_FeeWaiverOrReimbursementOverAssets (0.90%) [9]
Net Expenses (as a percentage of Assets) rr_NetExpensesOverAssets 2.01% [8]
Expense Example, with Redemption, 1 Year rr_ExpenseExampleYear01 $ 203
Expense Example, with Redemption, 3 Years rr_ExpenseExampleYear03 813
Expense Example, with Redemption, 5 Years rr_ExpenseExampleYear05 1,449
Expense Example, with Redemption, 10 Years rr_ExpenseExampleYear10 $ 3,159
Label rr_AverageAnnualReturnLabel Return Before Taxes
1 Year rr_AverageAnnualReturnYear01 42.89%
5 Years rr_AverageAnnualReturnYear05 10.73%
Since Inception rr_AverageAnnualReturnSinceInception 10.87% [6]
Inception Date rr_AverageAnnualReturnInceptionDate Oct. 16, 2012
[1] The NASDAQ Internet Index replaced the Bloomberg U.S. Internet Index, which was discontinued effective September 2017.
[2] The Distribution and/or Service (12b-1) Fees reflect the Board’s determination to reduce such fees payable under the distribution and service plan of the Fund from 0.35% to 0.25%, effective September 1, 2016 through at least January 2, 2022.
[3] Fund performance is shown beginning on February 1, 2010, which is the date the Rockland Small Cap Growth Fund (the “Predecessor Fund”) was reorganized into the Fund and the Adviser’s investment team took over management of the Predecessor Fund’s portfolio. The Predecessor Fund was managed by another investment advisory firm.
[4] The Distribution and/or Service (12b-1) Fees reflect the Board’s determination to reduce such fees payable under the distribution and service plan of the Fund, with respect to Investor Class shares, from 0.35% to 0.25%, effective September 1, 2016 through at least January 2, 2022.
[5] The Adviser has contractually agreed, through at least January 2, 2022, 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 fees and expenses, and extraordinary expenses) exceed 2.25% or 1.95% for Investor Class shares and Institutional Class shares, respectively, of each class’ 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 thirty-six (36) months following such fee waivers to the extent that such recoupment will not cause the Fund to exceed any applicable expense limitation that was in place for the Fund when the fees were waived. Please note that the maximum waiver is 0.80%, which means that the Fund’s overall expenses could exceed 2.25% for Investor Class shares or 1.95% for Institutional Class shares. This waiver agreement may only be terminated by the Board.
[6] Fund performance is shown beginning on October 16, 2012, which is when the Adviser’s investment team took over exclusive management of the Jacob Micro Cap Growth Fund (formerly, PineBridge US Micro Cap Growth Fund) (the “Predecessor Fund”), which was reorganized into the Fund on November 12, 2012. In previous years, the Predecessor Fund was managed by another investment advisory firm, and, from July 9, 2012 through October 15, 2012, it was managed by the Adviser along with the portfolio manager from the prior advisory firm. Performance information prior to October 16, 2012 is not shown.
[7] The Distribution and/or Service (12b-1) Fees reflect the Board’s determination to reduce such fees payable under the distribution and service plan of the Fund, with respect to Investor Class shares, from 0.35% to 0.25%, effective September 1, 2016 through at least January 2, 2022.
[8] Total Annual Fund Operating Expenses differs from the corresponding ratio of gross operating expenses to average net assets in the Financial Highlights section of the Prospectus because of the acquired fund fees and expenses noted above.
[9] The Adviser has contractually agreed, through at least January 2, 2022, 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 fees and expenses, and extraordinary expenses) exceed 2.30% or 2.00% for Investor Class shares and Institutional Class shares, respectively, of each class’ 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 thirty-six (36) months following such fee waivers to the extent that such recoupment will not cause the Fund to exceed any applicable expense limitation that was in place for the Fund when the fees were waived. Please note that the maximum waiver is 1.10%, which means that the Fund’s overall expenses could exceed 2.30% for Investor Class shares or 2.00% for Institutional Class shares. This waiver agreement may only be terminated by the Board.