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Label Element Value
Prospectus [Line Items] rr_ProspectusLineItems  
Document Type dei_DocumentType 485BPOS
Document Period End Date dei_DocumentPeriodEndDate Jun. 24, 2019
Entity Registrant Name dei_EntityRegistrantName RMB INVESTORS TRUST
Entity Central Index Key dei_EntityCentralIndexKey 0000030126
Amendment Flag dei_AmendmentFlag false
Document Creation Date dei_DocumentCreationDate Jun. 24, 2019
Document Effective Date dei_DocumentEffectiveDate Jun. 24, 2019
Prospectus Date rr_ProspectusDate Jun. 24, 2019
Entity Inv Company Type dei_EntityInvCompanyType N-1A
RMB Small Cap Fund  
Prospectus [Line Items] rr_ProspectusLineItems  
Risk/Return [Heading] rr_RiskReturnHeading RMB SMALL CAP FUND
Objective [Heading] rr_ObjectiveHeading Investment Objective.  
Objective, Primary [Text Block] rr_ObjectivePrimaryTextBlock
The RMB Small Cap Fund (the “Fund”) seeks capital appreciation.
Expense [Heading] rr_ExpenseHeading Fees and Expenses of the Fund
Expense Narrative [Text Block] rr_ExpenseNarrativeTextBlock
The following table describes the fees and expenses that you may pay if you buy and hold shares of the Fund.
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)
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 fiscal year ended June 30, 2018, the Predecessor Fund’s portfolio turnover rate was 20% of the average value of its portfolio.
Portfolio Turnover, Rate rr_PortfolioTurnoverRate 20.00%
Expense Example [Heading] rr_ExpenseExampleHeading Expense 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.
This 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, taking into account the Expense Cap in the first year 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 market conditions, at least 80% of its net assets (plus borrowings for investment purposes) in equity securities of U.S. companies with small market capitalizations. For this purpose, RMB Capital Management, LLC (the “Adviser”) defines a small capitalization company as any company with a market capitalization less than or equal to the largest market capitalization (determined at the time of investment) of any company in the Russell 2000® Index, which, as of May 31, 2019, was approximately $9.87 billion. The Fund may invest in sponsored and unsponsored American Depositary Receipts and/or Global Depositary Receipts, and may, and currently does (as of the date of this Prospectus), invest a significant portion of its assets in financial services companies.
The Adviser actively manages the Fund by applying an economic return framework, which measures the Fund’s return on investment and adjusts for factors such as inflation or accounting treatments. This is a valuation model that uses cash flow to determine a company’s value, rather than traditional accounting measures such as corporate performance, earnings and book value. The Adviser uses this methodology to identify attractively-priced companies, and as a result, the Fund invests primarily in growth and value-style equity securities.
The Adviser reduces positions or sells securities in the Fund for a variety of reasons, such as when the securities reach their target price or when a position would exceed 5% of the Fund’s net assets.
Risk [Heading] rr_RiskHeading Principal Investment Risks.
Risk Narrative [Text Block] rr_RiskNarrativeTextBlock
As with any mutual fund, there is no guarantee that the Fund will achieve its objective. The Fund’s share price fluctuates, which means you could lose money by investing in the Fund. The Fund is not a complete investment program and should be considered only as part of an investment portfolio. The principal risks of investing in the Fund are summarized as follows:
Market Risk.  This is the risk that the price of a security will fall due to changing economic, political or market conditions, or due to a company’s individual situation. The risk would be greater if any of the categories of securities that the Fund emphasizes fell out of favor with the market. Companies in the Fund’s portfolio could fail to achieve earnings estimates or other market expectations, causing their stock prices to drop.
Small-to-Medium Capitalization Risk.   Securities of companies with small-to-medium market capitalizations are often more volatile, less liquid and more susceptible to market pressures than securities of larger issuers.
Stock Selection Risk.  Individual stocks may decline in value or not increase in value, even when the stock market in general is rising.
Equity Securities Risk.  Equity securities, such as common stocks, are subject to greater volatility and chance of decline than other securities, such as fixed-income securities.
Management Risk.  There is no guarantee that the Adviser will choose investments that increase in value.
Growth Investing Risk. Growth companies are generally more susceptible than established companies to market events and sharp declines in value.
Value Investing Risk.  Value stocks may not increase in price, may not issue the anticipated stock dividends or may decline in price, based upon the market’s belief of the issuer’s intrinsic worth.
American Depositary Receipt (ADR) / Global Depositary Receipt (GDR) / European Depositary Receipts (“EDRs”) Risk. ADRs are receipts issued by U.S. banks evidencing ownership in securities of foreign issuers, and GDRs and EDRs are receipts issued by banks in more than one country evidencing ownership in securities of foreign issuers. Securities of foreign issuers, and consequently ADRs, GDRs, and EDRs, may decrease in value due to changes in currency exchange rates, the economic climate in the issuer’s home country or for a variety of other reasons.
Foreign Investing Risk. Foreign securities may underperform U.S. securities and may be more volatile than U.S. securities. Risks relating to investments in foreign securities (including depositary receipts) and to securities of issuers with significant exposure to foreign markets include currency exchange rate fluctuation; less available public information about the issuers of securities; less stringent regulatory standards; lack of uniform accounting, auditing and financial reporting standards; and country risks, including less liquidity, high inflation rates and unfavorable economic practices; and political instability and expropriation and nationalization risks.
Financial Services Risk.  Investing a significant portion of assets in the financial services sector may cause the Fund to be more sensitive to the risks and concerns facing financial companies, including banks, insurance companies, and capital markets companies. The financial services sector can be significantly affected by changes in interest rates, the rate of corporate and consumer debt defaults, the availability and cost of borrowing and raising capital, regulatory changes and price competition. Changing interest rates could reduce the profitability of certain types of companies in the financial services sector. For example, rising interest rates increase the cost of financing to, and may reduce the profitability of, certain financial services companies. The financial services sector may be subject to a greater risk of rising interest rates due to the current period of historically low rates and the federal funds rate increases recently initiated by the Federal Reserve.
REIT Risk. The Fund’s investments in real estate related securities (primarily real estate investment trusts (“REITs”)) are subject to the risk that the value of the real estate underlying the securities will go down, which can be caused by deteriorating economic conditions and rising interest rates, and may also be subject to the risk that borrowers or tenants may default on their payment obligations. Investments in REITs involve additional risks. REITs may have limited financial resources and real estate diversification and are dependent on specialized management skills. In addition, the failure of a REIT to qualify as a REIT for federal income tax purposes would adversely affect the REIT’s value.
Risk Lose Money [Text] rr_RiskLoseMoney The Fund’s share price fluctuates, which means you could lose money by investing in the Fund.
Bar Chart and Performance Table [Heading] rr_BarChartAndPerformanceTableHeading Performance.
Performance Narrative [Text Block] rr_PerformanceNarrativeTextBlock
The Fund is a new series of the Trust and has no performance history. As a result of the Reorganization, the performance and accounting history of the Predecessor Fund were assumed by the Fund’s Class I shares. For periods between July 23, 2010 and December 31, 2018, the Fund’s Class I performance shown is that of the Predecessor Fund. For periods prior to July 23, 2010, the performance shown is that of the Frontegra IronBridge Small Cap Fund. The Frontegra IronBridge Small Cap Fund commenced operations on August 30, 2002 and was reorganized into the Predecessor Fund on July 23, 2010 (the “Frontegra Reorganization”). As a result of the Frontegra Reorganization, the performance and accounting history of the Frontegra IronBridge Small Cap Fund were assumed by the Predecessor Fund.
The bar chart and table provide some indication of the risks of investing in the Fund by showing changes in the Fund’s performance from year to year and by showing how the Fund’s average annual total returns for 1, 5, and 10 years compared with those of a broad measure of market performance. Bear in mind that past performance (before and after taxes) is not a guarantee of future performance.
Updated performance information may be obtained on the Fund’s website at www.rmbfunds.com or by calling 1-800-462-2392.
Performance Information Illustrates Variability of Returns [Text] rr_PerformanceInformationIllustratesVariabilityOfReturns The bar chart and table provide some indication of the risks of investing in the Fund by showing changes in the Fund’s performance from year to year and by showing how the Fund’s average annual total returns for 1, 5, and 10 years compared with those of a broad measure of market performance.
Performance Availability Phone [Text] rr_PerformanceAvailabilityPhone 1-800-462-2392
Performance Availability Website Address [Text] rr_PerformanceAvailabilityWebSiteAddress www.rmbfunds.com
Performance Past Does Not Indicate Future [Text] rr_PerformancePastDoesNotIndicateFuture Bear in mind that past performance (before and after taxes) is not a guarantee of future performance.
Bar Chart [Heading] rr_BarChartHeading Calendar Year Total Returns Annual Total Returns for Small Cap Fund Class I Shares for the years ended December 31
Bar Chart Closing [Text Block] rr_BarChartClosingTextBlock
During the periods shown above, the highest return for the Fund (including its Predecessor Funds) for a calendar quarter was 21.90% (for the quarter ended June 30, 2009) and the lowest return for a calendar quarter was -20.35% (for the quarter ended September 30, 2011). The Fund’s year-to-date return as of March 31, 2019 was 14.95%.
Performance Table Heading rr_PerformanceTableHeading Average Annual Total Returns(1) (for the periods ended December 31, 2018)
Index No Deduction for Fees, Expenses, Taxes [Text] rr_IndexNoDeductionForFeesExpensesTaxes (reflects no deduction of fees, expenses or taxes)
Performance Table Uses Highest Federal Rate rr_PerformanceTableUsesHighestFederalRate After-tax returns are calculated using the highest individual federal marginal income tax rates in effect during each year of the periods shown and do not reflect the impact of state and local taxes.
Performance Table Not Relevant to Tax Deferred rr_PerformanceTableNotRelevantToTaxDeferred Your actual after-tax returns depend on your individual tax situation and likely will differ from the results shown above. After-tax returns are not relevant if you hold your Fund shares through a tax-advantaged arrangement, such as a 401(k) plan, individual retirement account (IRA) or 529 college savings plan.
Performance Table Explanation after Tax Higher rr_PerformanceTableExplanationAfterTaxHigher In certain cases, the “Return After Taxes on Distributions and Sale of Fund Shares” may be higher than other return figures for the same period. This will occur when a capital loss is realized upon the sale of Fund shares and provides an assumed tax benefit that increases the return.
Performance Table Footnotes rr_PerformanceTableFootnotesTextBlock
(1)
Investor Class shares have not commenced operations, are not available for purchase and do not have any returns.
Performance Table Closing [Text Block] rr_PerformanceTableClosingTextBlock
After-tax returns are calculated using the highest individual federal marginal income tax rates in effect during each year of the periods shown and do not reflect the impact of state and local taxes. In certain cases, the “Return After Taxes on Distributions and Sale of Fund Shares” may be higher than other return figures for the same period. This will occur when a capital loss is realized upon the sale of Fund shares and provides an assumed tax benefit that increases the return. Your actual after-tax returns depend on your individual tax situation and likely will differ from the results shown above. After-tax returns are not relevant if you hold your Fund shares through a tax-advantaged arrangement, such as a 401(k) plan, individual retirement account (IRA) or 529 college savings plan.
RMB Small Cap Fund | Russell 2000® Index (reflects no deductions for fees, expenses or taxes)  
Prospectus [Line Items] rr_ProspectusLineItems  
Label rr_AverageAnnualReturnLabel Russell 2000® Index (reflects no deduction for fees, expenses or taxes)
1 Year rr_AverageAnnualReturnYear01 (11.01%)
5 Years rr_AverageAnnualReturnYear05 4.41%
10 Years rr_AverageAnnualReturnYear10 11.97%
Since Inception rr_AverageAnnualReturnSinceInception 9.32%
Inception Date rr_AverageAnnualReturnInceptionDate Aug. 30, 2002
RMB Small Cap Fund | Investor Class  
Prospectus [Line Items] rr_ProspectusLineItems  
Management Fees (as a percentage of Assets) rr_ManagementFeesOverAssets 1.00%
Distribution and Service (12b-1) Fees rr_DistributionAndService12b1FeesOverAssets 0.25%
Other Expenses (as a percentage of Assets): rr_OtherExpensesOverAssets 0.21% [1]
Expenses (as a percentage of Assets) rr_ExpensesOverAssets 1.46%
Fee Waiver or Reimbursement rr_FeeWaiverOrReimbursementOverAssets (0.11%) [2]
Net Expenses (as a percentage of Assets) rr_NetExpensesOverAssets 1.35%
Fee Waiver or Reimbursement over Assets, Date of Termination rr_FeeWaiverOrReimbursementOverAssetsDateOfTermination 6/21/2019
Expense Example, with Redemption, 1 Year rr_ExpenseExampleYear01 $ 137
Expense Example, with Redemption, 3 Years rr_ExpenseExampleYear03 451
Expense Example, with Redemption, 5 Years rr_ExpenseExampleYear05 787
Expense Example, with Redemption, 10 Years rr_ExpenseExampleYear10 $ 1,737
RMB Small Cap Fund | Class I  
Prospectus [Line Items] rr_ProspectusLineItems  
Trading Symbol dei_TradingSymbol RMBBX
Management Fees (as a percentage of Assets) rr_ManagementFeesOverAssets 1.00%
Distribution and Service (12b-1) Fees rr_DistributionAndService12b1FeesOverAssets none
Other Expenses (as a percentage of Assets): rr_OtherExpensesOverAssets 0.21% [1]
Expenses (as a percentage of Assets) rr_ExpensesOverAssets 1.21%
Fee Waiver or Reimbursement rr_FeeWaiverOrReimbursementOverAssets (0.11%) [2]
Net Expenses (as a percentage of Assets) rr_NetExpensesOverAssets 1.10%
Fee Waiver or Reimbursement over Assets, Date of Termination rr_FeeWaiverOrReimbursementOverAssetsDateOfTermination 6/21/2019
Expense Example, with Redemption, 1 Year rr_ExpenseExampleYear01 $ 112
Expense Example, with Redemption, 3 Years rr_ExpenseExampleYear03 373
Expense Example, with Redemption, 5 Years rr_ExpenseExampleYear05 654
Expense Example, with Redemption, 10 Years rr_ExpenseExampleYear10 $ 1,456
Annual Return 2009 rr_AnnualReturn2009 24.53%
Annual Return 2010 rr_AnnualReturn2010 23.36%
Annual Return 2011 rr_AnnualReturn2011 (3.79%)
Annual Return 2012 rr_AnnualReturn2012 13.20%
Annual Return 2013 rr_AnnualReturn2013 33.26%
Annual Return 2014 rr_AnnualReturn2014 6.16%
Annual Return 2015 rr_AnnualReturn2015 (1.97%)
Annual Return 2016 rr_AnnualReturn2016 13.70%
Annual Return 2017 rr_AnnualReturn2017 10.43%
Annual Return 2018 rr_AnnualReturn2018 (4.97%)
Year to Date Return, Label rr_YearToDateReturnLabel year-to-date return
Bar Chart, Year to Date Return, Date rr_BarChartYearToDateReturnDate Mar. 31, 2019
Bar Chart, Year to Date Return rr_BarChartYearToDateReturn 14.95%
Highest Quarterly Return, Label rr_HighestQuarterlyReturnLabel highest return
Highest Quarterly Return, Date rr_BarChartHighestQuarterlyReturnDate Jun. 30, 2009
Highest Quarterly Return rr_BarChartHighestQuarterlyReturn 21.90%
Lowest Quarterly Return, Label rr_LowestQuarterlyReturnLabel lowest return
Lowest Quarterly Return, Date rr_BarChartLowestQuarterlyReturnDate Sep. 30, 2011
Lowest Quarterly Return rr_BarChartLowestQuarterlyReturn (20.35%)
Label rr_AverageAnnualReturnLabel Small Cap Fund - Class I Return Before Taxes
1 Year rr_AverageAnnualReturnYear01 (4.97%)
5 Years rr_AverageAnnualReturnYear05 4.43%
10 Years rr_AverageAnnualReturnYear10 10.72%
Since Inception rr_AverageAnnualReturnSinceInception 9.70%
Inception Date rr_AverageAnnualReturnInceptionDate Aug. 30, 2002
RMB Small Cap Fund | Class I | After Taxes on Distributions  
Prospectus [Line Items] rr_ProspectusLineItems  
Label rr_AverageAnnualReturnLabel Small Cap Fund - Class I Return After Taxes on Distributions
1 Year rr_AverageAnnualReturnYear01 (11.78%)
5 Years rr_AverageAnnualReturnYear05 0.47%
10 Years rr_AverageAnnualReturnYear10 8.35%
Since Inception rr_AverageAnnualReturnSinceInception 7.76%
RMB Small Cap Fund | Class I | After Taxes on Distributions and Sales  
Prospectus [Line Items] rr_ProspectusLineItems  
Label rr_AverageAnnualReturnLabel Small Cap Fund - Class I Return After Taxes on Distributions and Sale of Fund Shares
1 Year rr_AverageAnnualReturnYear01 2.41%
5 Years rr_AverageAnnualReturnYear05 3.37%
10 Years rr_AverageAnnualReturnYear10 8.85%
Since Inception rr_AverageAnnualReturnSinceInception 8.08%
RMB SMID Cap Fund  
Prospectus [Line Items] rr_ProspectusLineItems  
Risk/Return [Heading] rr_RiskReturnHeading RMB SMID CAP FUND
Objective [Heading] rr_ObjectiveHeading Investment Objective.  
Objective, Primary [Text Block] rr_ObjectivePrimaryTextBlock
The RMB SMID Cap Fund (“SMID Cap Fund”) seeks capital appreciation.
Expense [Heading] rr_ExpenseHeading Fees and Expenses of the Fund.
Expense Narrative [Text Block] rr_ExpenseNarrativeTextBlock
The following table describes the fees and expenses that you may pay if you buy and hold shares of the Fund.
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)
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 fiscal year ended June 30, 2018, the Predecessor Fund’s portfolio turnover rate was 14% of the average value of its portfolio.
Portfolio Turnover, Rate rr_PortfolioTurnoverRate 14.00%
Expense Example [Heading] rr_ExpenseExampleHeading Expense 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.
This 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 (taking into account the expense cap for one year).
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 market conditions, at least 80% of its net assets (plus borrowings for investment purposes) in equity securities of companies with small-to-medium market capitalizations.  For this purpose, the Adviser defines a small-to-medium capitalization company as a company that has a market capitalization of between $100 million and $10 billion at the time of purchase. The Fund may invest in sponsored and unsponsored American Depositary Receipts and/or Global Depositary Receipts, and may invest a significant portion of its assets in financial services companies.
The Adviser actively manages the Fund by applying an economic return framework, which measures the Fund’s return on investment and adjusts for factors such as inflation or accounting treatments. This is a valuation model that uses cash flow to determine a company’s value, rather than traditional accounting measures such as corporate performance, earnings and book value. The Adviser uses this methodology to identify attractively-priced companies, and as a result, the Fund invests primarily in growth and value-style equity securities.
The Adviser reduces positions or sells securities in the Fund for a variety of reasons, such as when the securities reach their target price or when a position would exceed 5% of the Fund’s net assets.
Risk [Heading] rr_RiskHeading Principal Investment Risks.
Risk Narrative [Text Block] rr_RiskNarrativeTextBlock
As with any mutual fund, there is no guarantee that the Fund will achieve its objective. The Fund’s share price fluctuates, which means you could lose money by investing in the Fund. The Fund is not a complete investment program and should be considered only as part of an investment portfolio. The principal risks of investing in the Fund are summarized as follows:
Market Risk.  This is the risk that the price of a security will fall due to changing economic, political or market conditions, or due to a company’s individual situation. The risk would be greater if any of the categories of securities that the Fund emphasizes fell out of favor with the market. Companies in the Fund’s portfolio could fail to achieve earnings estimates or other market expectations, causing their stock prices to drop.
Small-to-Medium Capitalization Risk.  Securities of companies with small-to-medium market capitalizations are often more volatile, less liquid and more susceptible to market pressures than securities of larger issuers.
Stock Selection Risk.  Individual stocks may decline in value or not increase in value, even when the stock market in general is rising.
Equity Securities Risk.  Equity securities, such as common stocks, are subject to greater volatility and chance of decline than other securities, such as fixed-income securities.
Management Risk.  There is no guarantee that the Adviser will choose investments that increase in value.
Growth Investing Risk. Growth companies are generally more susceptible than established companies to market events and sharp declines in value.
Value Investing Risk.  Value stocks may not increase in price, may not issue the anticipated stock dividends or may decline in price, based upon the market’s belief of the issuer’s intrinsic worth.
American Depositary Receipt (ADR) / Global Depositary Receipt (GDR) / European Depositary Receipts (“EDRs”) Risk. ADRs are receipts issued by U.S. banks evidencing ownership in securities of foreign issuers, and GDRs and EDRs are receipts issued by banks in more than one country evidencing ownership in securities of foreign issuers. Securities of foreign issuers, and consequently ADRs, GDRs, and EDRs may decrease in value due to changes in currency exchange rates, the economic climate in the issuer’s home country or for a variety of other reasons.
Foreign Investing Risk. Foreign securities may underperform U.S. securities and may be more volatile than U.S. securities. Risks relating to investments in foreign securities (including depositary receipts) and to securities of issuers with significant exposure to foreign markets include currency exchange rate fluctuation; less available public information about the issuers of securities; less stringent regulatory standards; lack of uniform accounting, auditing and financial reporting standards; and country risks, including less liquidity, high inflation rates and unfavorable economic practices; and political instability and expropriation and nationalization risks.
Financial Services Risk.  Investing a significant portion of assets in the financial services sector may cause the Fund to be more sensitive to the risks and concerns facing financial companies, including banks, insurance companies, and capital markets companies. The financial services sector can be significantly affected by changes in interest rates, the rate of corporate and consumer debt defaults, the availability and cost of borrowing and raising capital, regulatory changes and price competition. Changing interest rates could reduce the profitability of certain types of companies in the financial services sector. For example, rising interest rates increase the cost of financing to, and may reduce the profitability of, certain financial services companies. The financial services sector may be subject to a greater risk of rising interest rates due to the current period of historically low rates and the federal funds rate increases recently initiated by the Federal Reserve.
REIT Risk. The Fund’s investments in real estate related securities (primarily real estate investment trusts (“REITs”)) are subject to the risk that the value of the real estate underlying the securities will go down, which can be caused by deteriorating economic conditions and rising interest rates, and may also be subject to the risk that borrowers or tenants may default on their payment obligations. Investments in REITs involve additional risks. REITs may have limited financial resources and real estate diversification and are dependent on specialized management skills. In addition, the failure of a REIT to qualify as a REIT for federal income tax purposes would adversely affect the REIT’s value.
Risk Lose Money [Text] rr_RiskLoseMoney The Fund’s share price fluctuates, which means you could lose money by investing in the Fund.
Bar Chart and Performance Table [Heading] rr_BarChartAndPerformanceTableHeading Performance.
Performance Narrative [Text Block] rr_PerformanceNarrativeTextBlock
The Fund is a new series of the Trust and has no performance history. As a result of the Reorganization, the performance and accounting history of the Predecessor Fund were assumed by the Fund’s Class I shares. For periods between July 23, 2010 and December 31, 2018, the performance shown is that of the Predecessor Fund, which commenced operations on July 23, 2010. For periods prior to July 23, 2010, the performance shown is that of the IronBridge SMID Cap Fund’s predecessor, the Frontegra IronBridge SMID Cap Fund which commenced operations on December 31, 2004 and was reorganized into the IronBridge SMID Cap Fund on July 23, 2010. Upon the reorganizations, both the Frontegra IronBridge SMID Cap Fund and the IronBridge SMID Cap Fund assumed the financial and performance history of their respective predecessor SMID Fund’s Institutional Class shares, which maintained the same fees and expenses as the Fund. Keep in mind that past performance (before and after taxes) may not indicate how well the Fund will perform in the future.
The bar chart and table provide some indication of the risks of investing in the Fund by showing changes in the Fund’s performance from year to year and by showing how the Fund’s average annual total returns for 1, 5, and 10 years compared with those of a broad measure of market performance. Bear in mind that past performance (before and after taxes) is not a guarantee of future performance.
Updated performance information may be obtained on the Fund’s website at www.rmbfunds.com or by calling 1-800-462-2392.
Performance Information Illustrates Variability of Returns [Text] rr_PerformanceInformationIllustratesVariabilityOfReturns The bar chart and table provide some indication of the risks of investing in the Fund by showing changes in the Fund’s performance from year to year and by showing how the Fund’s average annual total returns for 1, 5, and 10 years compared with those of a broad measure of market performance.
Performance Availability Phone [Text] rr_PerformanceAvailabilityPhone 1-800-462-2392
Performance Availability Website Address [Text] rr_PerformanceAvailabilityWebSiteAddress www.rmbfunds.com
Performance Past Does Not Indicate Future [Text] rr_PerformancePastDoesNotIndicateFuture Bear in mind that past performance (before and after taxes) is not a guarantee of future performance.
Bar Chart [Heading] rr_BarChartHeading Calendar Year Total Returns Annual Total Returns for SMID Cap Fund Class I Shares for the years ended December 31
Bar Chart Closing [Text Block] rr_BarChartClosingTextBlock
During the periods shown above, the highest return for the SMID Cap Fund (including its Predecessor Funds) for a calendar quarter was 18.39% (for the quarter ended June 30, 2009) and the lowest return for a calendar quarter was -20.39% (for the quarter ended September 30, 2011). The Fund’s year-to-date return as of March 31, 2019 was 15.21%.
Performance Table Heading rr_PerformanceTableHeading Average Annual Total Returns(1) (for the periods ended December 31, 2018)
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 highest individual federal marginal income tax rates in effect during each year of the periods shown and do not reflect the impact of state and local taxes.
Performance Table Not Relevant to Tax Deferred rr_PerformanceTableNotRelevantToTaxDeferred Your actual after-tax returns depend on your individual tax situation and likely will differ from the results shown above. After-tax returns are not relevant if you hold your Fund shares through a tax-advantaged arrangement, such as a 401(k) plan, individual retirement account (IRA) or 529 college savings plan.
Performance Table Explanation after Tax Higher rr_PerformanceTableExplanationAfterTaxHigher In certain cases, the “Return After Taxes on Distributions and Sale of Fund Shares” may be higher than other return figures for the same period. This will occur when a capital loss is realized upon the sale of Fund shares and provides an assumed tax benefit that increases the return.
Performance Table Footnotes rr_PerformanceTableFootnotesTextBlock
(1)
Investor Class shares have not commenced operations, are not available for purchase and do not have any returns
Performance Table Closing [Text Block] rr_PerformanceTableClosingTextBlock
After-tax returns are calculated using the highest individual federal marginal income tax rates in effect during each year of the periods shown and do not reflect the impact of state and local taxes. In certain cases, the “Return After Taxes on Distributions and Sale of Fund Shares” may be higher than other return figures for the same period. This will occur when a capital loss is realized upon the sale of Fund shares and provides an assumed tax benefit that increases the return. Your actual after-tax returns depend on your individual tax situation and likely will differ from the results shown above. After-tax returns are not relevant if you hold your Fund shares through a tax-advantaged arrangement, such as a 401(k) plan, individual retirement account (IRA) or 529 college savings plan.
RMB SMID Cap Fund | Russell 2500® Index (reflects no deductions for fees, expenses or taxes)  
Prospectus [Line Items] rr_ProspectusLineItems  
Label rr_AverageAnnualReturnLabel Russell 2500® Index (reflects no deduction for fees, expenses or taxes)
1 Year rr_AverageAnnualReturnYear01 (10.00%)
5 Years rr_AverageAnnualReturnYear05 5.15%
10 Years rr_AverageAnnualReturnYear10 13.15%
Since Inception rr_AverageAnnualReturnSinceInception 7.55%
Inception Date rr_AverageAnnualReturnInceptionDate Dec. 31, 2004
RMB SMID Cap Fund | Investor Class  
Prospectus [Line Items] rr_ProspectusLineItems  
Management Fees (as a percentage of Assets) rr_ManagementFeesOverAssets 0.85%
Distribution and Service (12b-1) Fees rr_DistributionAndService12b1FeesOverAssets 0.25%
Other Expenses (as a percentage of Assets): rr_OtherExpensesOverAssets 0.18% [3]
Expenses (as a percentage of Assets) rr_ExpensesOverAssets 1.28% [4]
Fee Waiver or Reimbursement rr_FeeWaiverOrReimbursementOverAssets (0.07%) [5]
Net Expenses (as a percentage of Assets) rr_NetExpensesOverAssets 1.21% [4]
Fee Waiver or Reimbursement over Assets, Date of Termination rr_FeeWaiverOrReimbursementOverAssetsDateOfTermination 6/21/2019
Expense Example, with Redemption, 1 Year rr_ExpenseExampleYear01 $ 123
Expense Example, with Redemption, 3 Years rr_ExpenseExampleYear03 399
Expense Example, with Redemption, 5 Years rr_ExpenseExampleYear05 696
Expense Example, with Redemption, 10 Years rr_ExpenseExampleYear10 $ 1,539
RMB SMID Cap Fund | Class I  
Prospectus [Line Items] rr_ProspectusLineItems  
Trading Symbol dei_TradingSymbol RMBMX
Management Fees (as a percentage of Assets) rr_ManagementFeesOverAssets 0.85%
Distribution and Service (12b-1) Fees rr_DistributionAndService12b1FeesOverAssets none
Other Expenses (as a percentage of Assets): rr_OtherExpensesOverAssets 0.18% [3]
Expenses (as a percentage of Assets) rr_ExpensesOverAssets 1.03% [4]
Fee Waiver or Reimbursement rr_FeeWaiverOrReimbursementOverAssets (0.07%) [5]
Net Expenses (as a percentage of Assets) rr_NetExpensesOverAssets 0.96% [4]
Fee Waiver or Reimbursement over Assets, Date of Termination rr_FeeWaiverOrReimbursementOverAssetsDateOfTermination 6/21/2019
Expense Example, with Redemption, 1 Year rr_ExpenseExampleYear01 $ 98
Expense Example, with Redemption, 3 Years rr_ExpenseExampleYear03 321
Expense Example, with Redemption, 5 Years rr_ExpenseExampleYear05 562
Expense Example, with Redemption, 10 Years rr_ExpenseExampleYear10 $ 1,253
Annual Return 2009 rr_AnnualReturn2009 26.48%
Annual Return 2010 rr_AnnualReturn2010 25.51%
Annual Return 2011 rr_AnnualReturn2011 (2.82%)
Annual Return 2012 rr_AnnualReturn2012 12.70%
Annual Return 2013 rr_AnnualReturn2013 31.39%
Annual Return 2014 rr_AnnualReturn2014 3.66%
Annual Return 2015 rr_AnnualReturn2015 (0.87%)
Annual Return 2016 rr_AnnualReturn2016 12.28%
Annual Return 2017 rr_AnnualReturn2017 13.66%
Annual Return 2018 rr_AnnualReturn2018 (4.89%)
Year to Date Return, Label rr_YearToDateReturnLabel year-to-date return
Bar Chart, Year to Date Return, Date rr_BarChartYearToDateReturnDate Mar. 31, 2019
Bar Chart, Year to Date Return rr_BarChartYearToDateReturn 15.21%
Highest Quarterly Return, Label rr_HighestQuarterlyReturnLabel highest return
Highest Quarterly Return, Date rr_BarChartHighestQuarterlyReturnDate Jun. 30, 2009
Highest Quarterly Return rr_BarChartHighestQuarterlyReturn 18.39%
Lowest Quarterly Return, Label rr_LowestQuarterlyReturnLabel lowest return
Lowest Quarterly Return, Date rr_BarChartLowestQuarterlyReturnDate Sep. 30, 2011
Lowest Quarterly Return rr_BarChartLowestQuarterlyReturn (20.39%)
Label rr_AverageAnnualReturnLabel SMID Cap Fund Class I Return Before Taxes
1 Year rr_AverageAnnualReturnYear01 (4.89%)
5 Years rr_AverageAnnualReturnYear05 4.52%
10 Years rr_AverageAnnualReturnYear10 11.04%
Since Inception rr_AverageAnnualReturnSinceInception 6.71%
Inception Date rr_AverageAnnualReturnInceptionDate Dec. 31, 2004
RMB SMID Cap Fund | Class I | After Taxes on Distributions  
Prospectus [Line Items] rr_ProspectusLineItems  
Label rr_AverageAnnualReturnLabel SMID Cap Fund Class I Return After Taxes on Distributions
1 Year rr_AverageAnnualReturnYear01 (8.07%)
5 Years rr_AverageAnnualReturnYear05 1.10%
10 Years rr_AverageAnnualReturnYear10 8.96%
Since Inception rr_AverageAnnualReturnSinceInception 5.09%
RMB SMID Cap Fund | Class I | After Taxes on Distributions and Sales  
Prospectus [Line Items] rr_ProspectusLineItems  
Label rr_AverageAnnualReturnLabel SMID Cap Fund Class I Return After Taxes on Distributions and Sale of Fund Shares
1 Year rr_AverageAnnualReturnYear01 (0.86%)
5 Years rr_AverageAnnualReturnYear05 3.28%
10 Years rr_AverageAnnualReturnYear10 9.03%
Since Inception rr_AverageAnnualReturnSinceInception 5.37%
RMB Dividend Growth Fund  
Prospectus [Line Items] rr_ProspectusLineItems  
Risk/Return [Heading] rr_RiskReturnHeading RMB DIVIDEND GROWTH FUND
Objective [Heading] rr_ObjectiveHeading Investment Objective.  
Objective, Primary [Text Block] rr_ObjectivePrimaryTextBlock
The RMB Dividend Growth Fund (“the Fund”) seeks long term capital appreciation. Income is generally of less importance, meaning that it is a secondary goal.
Expense [Heading] rr_ExpenseHeading Fees and Expenses of the Fund.
Expense Narrative [Text Block] rr_ExpenseNarrativeTextBlock
The following table describes the fees and expenses that you may pay if you buy and hold shares of the Fund.
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)
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 fiscal year ended June 30, 2018, the Predecessor Fund’s portfolio turnover rate was 58% of the average value of its portfolio.
Portfolio Turnover, Rate rr_PortfolioTurnoverRate 58.00%
Expense Example [Heading] rr_ExpenseExampleHeading Expense 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.
This 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 (taking into account the expense cap for one year).
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 in equity securities of companies primarily with large market capitalizations.  For this purpose, the Adviser defines a large capitalization company as any company with a market capitalization in excess of $10 billion at the time of purchase, although the Fund may invest in companies with smaller market capitalizations from time to time. The Fund may invest in sponsored and unsponsored American Depositary Receipts and/or Global Depositary Receipts.
The Adviser actively manages the Fund through a fundamental, bottom up research approach. The Fund seeks to own a portfolio of companies which offer above average sustainable dividend growth by investing in high quality businesses managed by skilled allocators of capital, with a superior competitive position, improving return on investment, and growing cash flows. This approach seeks to avoids companies that unsustainably grow dividends purely by financial engineering, increasing leverage or simply selling productive assets and distributing proceeds to shareholders. The foundation of the strategy is the belief that stock prices follow earnings and cash flow growth over longer periods of time. The Fund invests in companies that have a history of increasing dividend payments and that the Adviser believes will be able to continue increasing dividend payments in future years. The Adviser believes that companies that increase their dividends have a below average risk profile compared to the overall market. The Fund may have more exposure to certain sectors (e.g. Information Technology) as a result of its investment strategy. The Fund may own a limited number of holdings (approximately 20 to 40 positions), but manages portfolio risk by diversifying across sectors and industries and avoiding companies with significant financial leverage.
The Fund’s holdings in a company are sold or reduced for a variety of reasons, including when the company reaches the target price established by the Adviser, the Adviser’s reason for investing in the company is no longer valid, a higher conviction investment opportunity presents itself or for diversification or portfolio repositioning purposes.
Risk [Heading] rr_RiskHeading Principal Investment Risks.
Risk Narrative [Text Block] rr_RiskNarrativeTextBlock
As with any mutual fund, there is no guarantee that the Fund will achieve its objective. The Fund’s share price fluctuates, which means you could lose money by investing in the Fund. The Fund is not a complete investment program and should be considered only as part of an investment portfolio. The principal risks of investing in the Fund are summarized as follows:
Market Risk.  This is the risk that the price of a security will fall due to changing economic, political or market conditions, or due to a company’s individual situation. The risk would be greater if any of the categories of securities that the Fund emphasizes fell out of favor with the market. Companies in the Fund’s portfolio could fail to achieve earnings estimates or other market expectations, causing their stock prices to drop.
Stock Selection Risk.  Individual stocks may decline in value or not increase in value, even when the stock market in general is rising.
Dividend Risk. This is the risk that an issuer of stock held by the Fund may choose not to declare a dividend or the dividend rate might not remain at current levels. Dividend paying stocks might not experience the same level of earnings growth or capital appreciation as non-dividend paying stocks. The Fund’s performance during a broad market advance could suffer because dividend paying stocks may not experience the same capital appreciation as non-dividend paying stocks. Large-cap stocks tend to go through cycles of doing better—or worse—than other segments of the stock market or the stock market in general. These periods have, in the past, lasted for as long as several years.
Limited Holdings Risk. Because the Fund tends to invest a high percentage of its assets in a smaller number of holdings, the Fund’s performance may be hurt disproportionately by the poor performance of relatively few positions.
Large-Cap Company Risk. Larger, more established companies may be unable to respond quickly to new competitive challenges, such as changes in consumer tastes or innovative smaller competitors. Also, large-cap companies are sometimes unable to attain the high growth rates of successful, smaller companies, especially during extended periods of economic expansion.
Small-to-Medium Capitalization Risk. Securities of companies with small-to-medium market capitalizations are often more volatile, less liquid and more susceptible to market pressures than securities of larger issuers.
Equity Securities Risk.  Equity securities, such as common stocks, are subject to greater volatility and chance of decline than other securities, such as fixed-income securities.
Management Risk.  There is no guarantee that the Adviser will choose investments that increase in value.
Technology Sector Risk. Information Technology companies face intense competition, both domestically and internationally, which may have an adverse effect on profit margins. Information Technology companies in which the Fund may invest, including software and services companies and technology hardware and equipment companies may have limited product lines, markets, financial resources or personnel. The products of Information Technology companies may face obsolescence due to rapid technological developments and frequent new product introduction, unpredictable changes in growth rates and competition for the services of qualified personnel. Companies in the Information Technology sector are heavily dependent on patent and intellectual property rights. The loss or impairment of these rights may adversely affect the profitability of these companies.
American Depositary Receipt (ADR) / Global Depositary Receipt (GDR) / European Depositary Receipts (“EDRs”) Risk. ADRs are receipts issued by U.S. banks evidencing ownership in securities of foreign issuers, and GDRs and EDRs are receipts issued by banks in more than one country evidencing ownership in securities of foreign issuers. Securities of foreign issuers, and consequently ADRs, GDRs, and EDRs may decrease in value due to changes in currency exchange rates, the economic climate in the issuer’s home country or for a variety of other reasons.
Foreign Investing Risk. Foreign securities may underperform U.S. securities and may be more volatile than U.S. securities. Risks relating to investments in foreign securities (including depositary receipts) and to securities of issuers with significant exposure to foreign markets include currency exchange rate fluctuation; less available public information about the issuers of securities; less stringent regulatory standards; lack of uniform accounting, auditing and financial reporting standards; and country risks, including less liquidity, high inflation rates and unfavorable economic practices; and political instability and expropriation and nationalization risks.
Risk Lose Money [Text] rr_RiskLoseMoney The Fund’s share price fluctuates, which means you could lose money by investing in the Fund.
Bar Chart and Performance Table [Heading] rr_BarChartAndPerformanceTableHeading Performance.
Performance Narrative [Text Block] rr_PerformanceNarrativeTextBlock
The Fund is a new series of the Trust and has no performance history. As a result of the Reorganization, the performance and accounting history of the Predecessor Fund were assumed by the Fund’s Class I shares. For periods prior to December 31, 2018, the performance shown is that of the Predecessor Fund. The IronBridge Large Cap Fund commenced operations on March 30, 2012 and was reorganized into the Fund on June 21, 2019. Upon reorganization, the Fund assumed the financial and performance history of the IronBridge Large Cap Fund, which maintained the same fees and expenses as the Fund. Keep in mind that past performance (before and after taxes) may not indicate how well the Fund will perform in the future.
The bar chart and table provide some indication of the risks of investing in the Fund by showing changes in the Fund’s performance from year to year and by showing how the Fund’s average annual total returns for 1, 5, and 10 years compared with those of a broad measure of market performance. Bear in mind that past performance (before and after taxes) is not a guarantee of future performance.
Updated performance information may be obtained on the Fund’s website at www.rmbfunds.com or by calling 1-800-462-2392.
Performance Information Illustrates Variability of Returns [Text] rr_PerformanceInformationIllustratesVariabilityOfReturns The bar chart and table provide some indication of the risks of investing in the Fund by showing changes in the Fund’s performance from year to year and by showing how the Fund’s average annual total returns for 1, 5, and 10 years compared with those of a broad measure of market performance.
Performance Availability Phone [Text] rr_PerformanceAvailabilityPhone 1-800-462-2392
Performance Availability Website Address [Text] rr_PerformanceAvailabilityWebSiteAddress www.rmbfunds.com
Performance Past Does Not Indicate Future [Text] rr_PerformancePastDoesNotIndicateFuture Bear in mind that past performance (before and after taxes) is not a guarantee of future performance.
Bar Chart [Heading] rr_BarChartHeading Calendar Year Total Returns Annual Total Returns for Dividend Growth Fund Class I Shares for the years ended December 31
Bar Chart Closing [Text Block] rr_BarChartClosingTextBlock
During the periods shown above, the highest return for the Fund (including its Predecessor Fund) for a calendar quarter was 8.71% (for the quarter ended December 31, 2013) and the lowest return for a calendar quarter was -11.10% (for the quarter ended December 31, 2018). The Fund’s year-to-date return as of March 31, 2019 was 12.94%.
Performance Table Heading rr_PerformanceTableHeading Average Annual Total Returns(1) (for the periods ended December 31, 2018)
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 highest individual federal marginal income tax rates in effect during each year of the periods shown and do not reflect the impact of state and local taxes.
Performance Table Not Relevant to Tax Deferred rr_PerformanceTableNotRelevantToTaxDeferred Your actual after-tax returns depend on your individual tax situation and likely will differ from the results shown above. After-tax returns are not relevant if you hold your Fund shares through a tax-advantaged arrangement, such as a 401(k) plan, individual retirement account (IRA) or 529 college savings plan.
Performance Table Explanation after Tax Higher rr_PerformanceTableExplanationAfterTaxHigher In certain cases, the “Return After Taxes on Distributions and Sale of Fund Shares” may be higher than other return figures for the same period. This will occur when a capital loss is realized upon the sale of Fund shares and provides an assumed tax benefit that increases the return.
Performance Table Footnotes rr_PerformanceTableFootnotesTextBlock

(1)
Investor Class shares have not commenced operations, are not available for purchase and do not have any returns
Performance Table Closing [Text Block] rr_PerformanceTableClosingTextBlock
After-tax returns are calculated using the highest individual federal marginal income tax rates in effect during each year of the periods shown and do not reflect the impact of state and local taxes. In certain cases, the “Return After Taxes on Distributions and Sale of Fund Shares” may be higher than other return figures for the same period. This will occur when a capital loss is realized upon the sale of Fund shares and provides an assumed tax benefit that increases the return. Your actual after-tax returns depend on your individual tax situation and likely will differ from the results shown above. After-tax returns are not relevant if you hold your Fund shares through a tax-advantaged arrangement, such as a 401(k) plan, individual retirement account (IRA) or 529 college savings plan.
RMB Dividend Growth Fund | Russell 1000® Index (reflects no deduction for fees, expense or taxes)  
Prospectus [Line Items] rr_ProspectusLineItems  
Label rr_AverageAnnualReturnLabel Russell 1000® Index (reflects no deduction for fees, expenses or taxes)
1 Year rr_AverageAnnualReturnYear01 (4.78%)
5 Years rr_AverageAnnualReturnYear05 8.21%
Since Inception rr_AverageAnnualReturnSinceInception 11.10%
Inception Date rr_AverageAnnualReturnInceptionDate Mar. 30, 2012
RMB Dividend Growth Fund | Investor Class  
Prospectus [Line Items] rr_ProspectusLineItems  
Management Fees (as a percentage of Assets) rr_ManagementFeesOverAssets 0.65%
Distribution and Service (12b-1) Fees rr_DistributionAndService12b1FeesOverAssets 0.25%
Other Expenses (as a percentage of Assets): rr_OtherExpensesOverAssets 0.55% [6]
Expenses (as a percentage of Assets) rr_ExpensesOverAssets 1.45% [7]
Fee Waiver or Reimbursement rr_FeeWaiverOrReimbursementOverAssets (0.39%) [8]
Net Expenses (as a percentage of Assets) rr_NetExpensesOverAssets 1.06% [7]
Fee Waiver or Reimbursement over Assets, Date of Termination rr_FeeWaiverOrReimbursementOverAssetsDateOfTermination 6/21/2019
Expense Example, with Redemption, 1 Year rr_ExpenseExampleYear01 $ 108
Expense Example, with Redemption, 3 Years rr_ExpenseExampleYear03 420
Expense Example, with Redemption, 5 Years rr_ExpenseExampleYear05 755
Expense Example, with Redemption, 10 Years rr_ExpenseExampleYear10 $ 1,702
RMB Dividend Growth Fund | Class I  
Prospectus [Line Items] rr_ProspectusLineItems  
Trading Symbol dei_TradingSymbol RMBDX
Management Fees (as a percentage of Assets) rr_ManagementFeesOverAssets 0.65%
Distribution and Service (12b-1) Fees rr_DistributionAndService12b1FeesOverAssets none
Other Expenses (as a percentage of Assets): rr_OtherExpensesOverAssets 0.55% [6]
Expenses (as a percentage of Assets) rr_ExpensesOverAssets 1.20% [7]
Fee Waiver or Reimbursement rr_FeeWaiverOrReimbursementOverAssets (0.39%) [8]
Net Expenses (as a percentage of Assets) rr_NetExpensesOverAssets 0.81% [7]
Fee Waiver or Reimbursement over Assets, Date of Termination rr_FeeWaiverOrReimbursementOverAssetsDateOfTermination 6/21/2019
Expense Example, with Redemption, 1 Year rr_ExpenseExampleYear01 $ 83
Expense Example, with Redemption, 3 Years rr_ExpenseExampleYear03 342
Expense Example, with Redemption, 5 Years rr_ExpenseExampleYear05 622
Expense Example, with Redemption, 10 Years rr_ExpenseExampleYear10 $ 1,420
Annual Return 2013 rr_AnnualReturn2013 28.57%
Annual Return 2014 rr_AnnualReturn2014 10.45%
Annual Return 2015 rr_AnnualReturn2015 3.35%
Annual Return 2016 rr_AnnualReturn2016 9.30%
Annual Return 2017 rr_AnnualReturn2017 18.53%
Annual Return 2018 rr_AnnualReturn2018 (1.25%)
Year to Date Return, Label rr_YearToDateReturnLabel year-to-date return
Bar Chart, Year to Date Return, Date rr_BarChartYearToDateReturnDate Mar. 31, 2019
Bar Chart, Year to Date Return rr_BarChartYearToDateReturn 12.94%
Highest Quarterly Return, Label rr_HighestQuarterlyReturnLabel highest return
Highest Quarterly Return, Date rr_BarChartHighestQuarterlyReturnDate Dec. 31, 2013
Highest Quarterly Return rr_BarChartHighestQuarterlyReturn 8.71%
Lowest Quarterly Return, Label rr_LowestQuarterlyReturnLabel lowest return
Lowest Quarterly Return, Date rr_BarChartLowestQuarterlyReturnDate Dec. 31, 2018
Lowest Quarterly Return rr_BarChartLowestQuarterlyReturn (11.10%)
Label rr_AverageAnnualReturnLabel Dividend Growth Fund – Class I Return Before Taxes
1 Year rr_AverageAnnualReturnYear01 (1.25%)
5 Years rr_AverageAnnualReturnYear05 7.87%
Since Inception rr_AverageAnnualReturnSinceInception 10.16%
Inception Date rr_AverageAnnualReturnInceptionDate Mar. 30, 2012
RMB Dividend Growth Fund | Class I | After Taxes on Distributions  
Prospectus [Line Items] rr_ProspectusLineItems  
Label rr_AverageAnnualReturnLabel Dividend Growth Fund – Class I Return After Taxes on Distributions
1 Year rr_AverageAnnualReturnYear01 (5.03%)
5 Years rr_AverageAnnualReturnYear05 5.88%
Since Inception rr_AverageAnnualReturnSinceInception 8.42%
RMB Dividend Growth Fund | Class I | After Taxes on Distributions and Sales  
Prospectus [Line Items] rr_ProspectusLineItems  
Label rr_AverageAnnualReturnLabel Dividend Growth Fund – Class I Return After Taxes on Distributions and Sale of Fund Shares
1 Year rr_AverageAnnualReturnYear01 2.23%
5 Years rr_AverageAnnualReturnYear05 6.08%
Since Inception rr_AverageAnnualReturnSinceInception 8.02%
[1] The Fund is newly formed and commenced operations following the completion of the reorganization of the IronBridge Small Cap Fund (the “Predecessor Fund”), a series of IronBridge Funds, Inc., into the Fund, which occurred on June 21, 2019 (the “Reorganization”). Other Expenses are estimated based on fees and expenses incurred by the Predecessor Fund, adjusted for anticipated changes in certain expenses applicable to other funds within the RMB fund complex.
[2] RMB Capital Management, LLC (the “Adviser”) has contractually agreed to reduce its compensation due from and/or assume expenses of the Fund to the extent necessary to ensure that the Fund’s operating expenses (excluding, interest, taxes, brokerage commissions and other transaction costs, expenditures that are capitalized in accordance with generally accepted accounting principles, acquired fund fees and expenses, if any, and other extraordinary expenses not incurred in the ordinary course of business) do not exceed 1.35% and 1.10% of the average net assets of the Fund’s Investor Class and Class I, respectively. The expense limitation agreement will remain in effect for one year after commencement of operations and cannot be terminated prior thereto without the approval of the Board of Trustees of RMB Investors Trust (the “Trust”). To the extent the Adviser waives its compensation and/or assumes expenses to satisfy the limitation, the Adviser may seek repayment by the Fund of a portion or all of such amounts at any time within three years from the date on which such amounts were waived or assumed (except that amounts waived or assumed with respect to the Predecessor Fund are not eligible for repayment after completion of the Reorganization), provided that the Fund is able to make the repayment without exceeding the lesser of the expense limitation in effect at the time of the waiver/reimbursement or in effect at the time of the repayment.
[3] The Fund is newly formed and commenced operations following the completion of the reorganization of the IronBridge SMID Cap Fund (the “Predecessor Fund”), a series of IronBridge Funds, Inc., into the Fund, which occurred on June 21, 2019 (the “Reorganization”). Other Expenses are estimated based on fees and expenses incurred by the Predecessor Fund, adjusted for anticipated changes in certain expenses applicable to other funds within the RMB fund complex.
[4] The Total Annual Fund Operating Expenses for the Fund may not correlate to the Ratio of Expenses to Average Net Assets in the Financial Highlights which reflects the operating expenses of the Funds and does not include acquired fund fees and expenses (“AFFE”). AFFE is estimated for the current fiscal year based on AFFE for the Predecessor Fund. AFFE is estimated to be less than 0.01%.
[5] RMB Capital Management, LLC (the “Adviser”) has contractually agreed to reduce its compensation due from and/or assume expenses of the Fund to the extent necessary to ensure that the Fund’s operating expenses (excluding interest, taxes, brokerage commissions and other transaction costs, expenditures that are capitalized in accordance with generally accepted accounting principles and acquired fund fees and expenses, if any, and other extraordinary expenses not incurred in the ordinary course of business) do not exceed 0.95% and 1.20% of the average net assets of the Fund’s Class I and Investor Class, respectively. The expense limitation agreement will remain in effect for one year after commencement of operations and cannot be terminated prior thereto without the approval of the Board of Trustees of RMB Investors Trust (the “Trust”). To the extent the Adviser waives its compensation and/or assumes expenses to satisfy the limitation, the Adviser may seek repayment by the Fund of a portion or all of such amounts at any time within three years from the date on which such amounts were waived or assumed (except that amounts waived or assumed with respect to the Predecessor Fund are not eligible for repayment after completion of the Reorganization), provided that the Fund is able to make the repayment without exceeding the lesser of the expense limitation in effect at the time of the waiver/reimbursement or in effect at the time of the repayment.
[6] The Fund is newly formed and commenced operations following the completion of the reorganization of the IronBridge Large Cap Fund (the “Predecessor Fund”), a series of IronBridge Funds, Inc., into the Fund, which occurred on June 21, 2019 (the “Reorganization”). Other Expenses are estimated based on fees and expenses incurred by the Predecessor Fund, adjusted for anticipated changes in certain expenses applicable to other funds within the RMB fund complex.
[7] The Total Annual Fund Operating Expenses for the Fund do not correlate to the Ratio of Expenses to Average Net Assets in the Financial Highlights which reflects the operating expenses of the Funds and does not include acquired fund fees and expenses (“AFFE”). AFFE is estimated for the current fiscal year based on AFFE for the Predecessor Fund. AFFE is estimated to be less than 0.01%.
[8] RMB Capital Management, LLC (the “Adviser”) has contractually agreed to reduce its compensation due from and/or assume expenses of the Fund to the extent necessary to ensure that the Fund’s operating expenses (excluding interest, taxes, brokerage commissions and other transaction costs, expenditures that are capitalized in accordance with generally accepted accounting principles, acquired fund fees and expenses, if any, and other extraordinary expenses not incurred in the ordinary course of business) do not exceed 0.80% and 1.05% of the average net assets of the Fund’s Class I and Investor Class, respectively. The expense limitation agreement will remain in effect for one year after commencement of operations and cannot be terminated prior thereto without the approval of the Board of Trustees of RMB Investors Trust (the “Trust”). To the extent the Adviser waives its compensation and/or assumes expenses to satisfy the limitation, the Adviser may seek repayment by the Fund of a portion or all of such amounts at any time within three years from the date on which such amounts were waived or assumed (except that amounts waived or assumed with respect to the Predecessor Fund are not eligible for repayment after completion of the Reorganization), provided that the Fund is able to make the repayment without exceeding the lesser of the expense limitation in effect at the time of the waiver/reimbursement or in effect at the time of the repayment.