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THE WATER ISLAND CREDIT OPPORTUNITIES FUND  
Risk/Return: rr_RiskReturnAbstract  
Risk/Return [Heading] rr_RiskReturnHeading THE WATER ISLAND CREDIT OPPORTUNITIES FUND (formerly The Arbitrage Credit Opportunities Fund)
Objective [Heading] rr_ObjectiveHeading Investment Objective
Objective, Primary [Text Block] rr_ObjectivePrimaryTextBlock

The Fund seeks to provide current income and capital growth.
Expense [Heading] rr_ExpenseHeading Fund Fees and Expenses
Expense Narrative [Text Block] rr_ExpenseNarrativeTextBlock

This table describes the fees and expenses that you may pay if you buy and hold shares of the Fund. You may qualify for sales charge discounts on Class A Shares if you and your family invest, or agree to invest in the future, at least $100,000 in the Fund. More information about these and other discounts is available from your financial professional and in "How to Purchase Shares" beginning on page 48 of the statutory prospectus and in Appendix A to the prospectus, titled "Intermediary-Specific Sales Charge Reductions and Waivers."
Shareholder Fees Caption [Text] rr_ShareholderFeesCaption Shareholder Fees (fees paid directly from your investment)
Operating Expenses Caption [Text] rr_OperatingExpensesCaption Annual Fund Operating Expenses (expenses that you pay each year as a percentage of the value of your investment)
Fee Waiver or Reimbursement over Assets, Date of Termination rr_FeeWaiverOrReimbursementOverAssetsDateOfTermination Sep. 30, 2020
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 314% of the average value of its portfolio.
Portfolio Turnover, Rate rr_PortfolioTurnoverRate 314.00%
Expenses Restated to Reflect Current [Text] rr_ExpensesRestatedToReflectCurrent Information has been restated to reflect current fees.
Expenses Not Correlated to Ratio Due to Acquired Fund Fees [Text] rr_ExpensesNotCorrelatedToRatioDueToAcquiredFundFees The operating expenses in this fee table do not correlate to the expense ratio in the financial highlights, but rather are restated to reflect the Fund's current (i) expense levels and (ii) expense limitation agreement.
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. It 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 expenses are equal to the Total Annual Fund Operating Expenses After Fee Waiver for the first year and equal to the Total Annual Fund Operating Expenses for the remaining years. Although your actual costs may be higher or lower, based on these assumptions your costs would be:
Expense Example, No Redemption, By Year, Caption [Text] rr_ExpenseExampleNoRedemptionByYearCaption You would pay the following expenses if you did not redeem your shares:
Strategy [Heading] rr_StrategyHeading Principal Investment Strategies
Strategy Narrative [Text Block] rr_StrategyNarrativeTextBlock

The Fund invests primarily in a portfolio of debt securities including corporate bonds and debentures (including high yield bonds commonly known as "junk bonds"), bank loans, convertible and preferred securities, credit default swaps and other debt instruments and derivatives that the Fund's investment adviser believes have debt-like characteristics. The Fund invests in both domestic and foreign debt securities. The principal types of derivatives in which the Fund may invest are credit default swaps, interest rate swaps, total return swaps, futures and options.


The Fund invests primarily in debt securities whose returns the adviser believes will be more correlated with the outcome of specific catalysts or events rather than overall market direction. These catalysts and events include mergers, acquisitions, debt maturities, refinancings, regulatory changes, recapitalizations, reorganizations, restructurings and other special situations. The Fund also uses a relative value approach and may express positive views on specific issuers by taking long positions in cash bonds and/or derivatives and negative views on specific issuers by taking short positions in cash bonds and/or derivatives. The Fund uses fundamental research to identify mispricings or inefficiencies in these situations and assesses their potential impact on security prices.


The Fund may engage in short-term trading strategies, and may engage in short sales and invest in derivatives. The principal short-term trading strategies may at times include convertible arbitrage, merger arbitrage, and capital structure arbitrage, which are discussed below. The Fund may seek to mitigate the risk of volatility (the appreciation or depreciation of the value of a security over a period of time) and duration (the impact of interest rate changes on fixed-income securities) by engaging in short sales and/or investing in derivatives, including credit default swaps, interest rate swaps, futures and options. The Fund may purchase or sell short equity securities or derivatives as part of a hedging strategy or hold equity positions or other assets that the Fund receives as part of a reorganization process. The Fund may, but is not required to, seek to reduce currency risk by hedging part or all of its exposure to various foreign currencies. Furthermore, the Fund may invest in exchange traded funds ("ETFs").


The Fund is not limited with respect to its portfolio maturity or duration. The Fund may invest in debt securities without regard to their credit ratings, including securities that are unrated, and in debt securities with a wide variety of terms that may vary from security to security, including but not limited to optional and mandatory prepayment provisions, fixed, variable, semi-variable, and resettable interest rates and conversion options, as well as various combinations of these terms.


Merger Arbitrage: Merger arbitrage is a highly specialized investment approach designed to profit from the successful completion of mergers, takeovers, tender offers, leveraged buyouts, spin-offs, liquidations and other corporate reorganizations. The most common merger arbitrage activity, and the approach the Fund generally uses, involves purchasing debt securities of an announced acquisition target company at a discount to their expected value upon completion of the acquisition. The Fund may engage in selling securities short when the terms of a proposed acquisition call for the exchange of common stock and/or other securities. In such a case, the securities of the company to be acquired may be purchased and, at approximately the same time, an amount of the acquiring company's common stock and/or other securities as per the terms of the transaction may be sold short.


Convertible Arbitrage: Convertible arbitrage is a specialized strategy that seeks to profit from pricing inefficiencies between a firm's convertible securities and its underlying equity. The most common convertible arbitrage approach, and the strategy the Fund generally uses, matches a long position in the convertible security with a short position in the underlying common stock. The Fund seeks to purchase convertible securities at discounts to their expected future values and sell short shares of the underlying common stock in order to mitigate equity market movements. As stock prices rise and the convertible security becomes more equity sensitive, the Fund may sell short additional common shares in order to maintain the relationship between the convertible and the underlying common stock. As stock prices fall, the Fund will typically buy back a portion of shares which it had sold short. Positions are typically designed to earn income from coupon or dividend payments and net gains from the purchase and sale of the convertible securities' positions and the underlying common stocks.


Capital Structure Arbitrage: Capital structure arbitrage seeks to profit from relative pricing discrepancies between related debt and/or equity securities. For example, when the Fund believes that unsecured securities are overvalued in relation to senior secured securities, the Fund may purchase a senior secured security of an issuer and sell short an unsecured security of the same issuer. In this example the trade would be profitable if credit quality spreads widened or if the issuer went bankrupt and the recovery rate for the senior debt was higher than anticipated. It is expected that, over time, the relative mispricing of the securities may decline, at which point the position will be liquidated.
Risk [Heading] rr_RiskHeading Principal Risks
Risk Narrative [Text Block] rr_RiskNarrativeTextBlock

As with all mutual funds, investing in the Fund entails risks that could cause the Fund and you to lose money. The principal risks of investing in the Fund are as follows:


Active Management Risk: The Fund is an actively managed investment portfolio and is therefore subject to management risk. The Adviser will apply its investment and risk analysis in making investment decisions for the Fund, but there is no guarantee that these decisions will produce the intended results.


Concentration Risk: The Adviser expects the Fund's assets to be invested in various industries; however, if, for example, a large percentage of corporate events taking place within the U.S. are within one industry over a given period of time, a large portion of the Fund's assets could be concentrated in that industry for that period of time. During such a period of concentration, the Fund may be subject to greater volatility and with respect to portfolio securities than a fund that is more broadly diversified.


Convertible Security Risks: Convertible securities generally offer lower interest or dividend yields than non-convertible securities of similar quality. Because convertible securities are higher in the firm's capital structure than equity, convertible securities are generally not as risky as the equity securities of the same issuer. However, convertible securities may gain or lose value due to changes in interest rates and other general economic conditions, industry fundamentals, market sentiment and changes in the issuer's operating results and credit ratings.


Counterparty Risk: The Fund may enter into various types of derivative contracts. These derivative contracts may be privately negotiated in the over-the-counter market. These contracts also involve exposure to credit risk, since contract performance depends in part on the financial condition of the counterparty. If a privately negotiated over-the-counter contract calls for payments by the Fund, the Fund must be prepared to make such payments when due. In addition, if the creditworthiness of the counterparty declines, the Fund may not receive payments owed under the contract, or such payments may be delayed and the value of agreements with the counterparty can be expected to decline, potentially resulting in losses to the Fund.


Credit Risks: Credit risk refers to the possibility that the issuer of the security will not be able to make interest or principal payments when due. The Fund may invest in convertible and non-convertible debt securities, including high yield debt securities, also known as "junk bonds." Investments in junk bonds are subject to greater credit risks than securities with credit ratings above investment grade and have a greater risk of default than investment grade debt securities. Junk bonds are less sensitive to interest rate changes than higher credit quality instruments and generally are more sensitive to adverse economic changes or individual corporate developments.


Currency Risks: Fluctuations in exchange rates between the U.S. dollar and foreign currencies may negatively affect an investment. Adverse changes in exchange rates may erode or reverse any gains produced by foreign currency denominated investments and may widen any losses. Currency forward/futures contracts also may deny the Fund from realizing gains from an increase in the value of the currency. In addition to currency risk, currency forward/futures contracts, like other derivatives, may be susceptible to credit risk and other risks.


Derivatives Risk: In general, a derivative instrument typically involves leverage and provides exposure to potential gain or loss from a change in the market price of the underlying asset (or a basket of assets or an index) in a notional amount that exceeds the amount of cash or assets required to establish or maintain the derivative instrument. Adverse changes in the value or price of the underlying asset (or basket of assets or index), which the Fund may not directly own, can result in a loss to the Fund substantially greater than the amount invested in the derivative itself. The use of derivative instruments also exposes the Fund to additional risks and transaction costs. Derivative instruments come in many varieties and may include forward contracts, options (both written and purchased) and swap contracts.


Foreign Securities Risks: The securities of foreign issuers may be less liquid and more volatile than securities of comparable U.S. issuers. The costs associated with securities transactions may be higher in foreign countries than in the United States. The U.S. dollar value of foreign securities traded in foreign currencies (and any dividends and interest earned) held by the Fund or by mutual funds in which the Fund invests may be affected favorably or unfavorably by changes in foreign currency exchange rates. An increase in the U.S. dollar relative to these other currencies may adversely affect the Fund. Additionally, investments in foreign securities, even those publicly traded in the United States, may involve risks which are in addition to those inherent in U.S. investments. Foreign companies may not be subject to the same regulatory requirements of U.S. companies, and as a consequence, there may be less publicly available information about such companies. Also, foreign companies may not be subject to uniform accounting, auditing, and financial reporting standards and requirements comparable to those applicable to U.S. companies. Foreign governments and foreign economies often are less stable than the U.S. Government and the U.S. economy.


Hedging Transaction Risk: The success of the Fund's hedging strategies will be subject to the Adviser's ability to assess correctly the degree of correlation between the performance of the instruments used in the hedging strategies and the performance of the investments in the Fund's portfolio being hedged. Hedging transactions involve the risk of imperfect correlation. Imperfect correlation may prevent the Fund from achieving the intended hedge or expose the Fund to risk of loss. Hedging transactions also limit the opportunity for gain if the value of a hedged portfolio position should increase.


High Portfolio Turnover Risks: The Fund's investment strategies may result in high portfolio turnover rates. This may increase the Fund's brokerage commission costs, which would reduce performance. Rapid portfolio turnover also exposes shareholders to a higher current realization of short-term gains which could cause you to pay higher taxes.


Interest Rate Risks: Prices of debt securities and preferred stocks tend to move inversely with changes in interest rates. When interest rates fall, the market value of the respective debt securities and preferred securities usually increases. Conversely, when interest rates rise, the market value of the respective debt securities and preferred securities usually declines. As such, a change in interest rates may affect prices of the Fund's debt securities and preferred securities and, accordingly, the Fund's share price.


Investment Company and ETF Risk: Investing in securities issued by other investment companies, including ETFs, involves risks similar to those of investing directly in the securities and other assets held by the investment company or ETF. Unlike shares of typical mutual funds, shares of ETFs are traded on an exchange through a trading day and bought and sold based on market values and not at net asset value. For this reason, shares could trade either at a premium or a discount to net asset value. The trading price of an ETF is expected to closely track the actual net asset value of an ETF, and the Fund will generally gain or lose value consistent with the performance of the ETF's portfolio securities. The Fund will pay brokerage commissions in connection with the purchase and sale of shares of ETFs. In addition, the Fund will indirectly bear its pro rata share of the fees and expenses incurred by a fund it invests in, including advisory fees. These expenses are in addition to the advisory and other expenses that the Fund bears directly in connection with its own operations. An ETF may not replicate exactly the performance of the benchmark index it seeks to track for a number of reasons, including transaction costs incurred by the ETF, the temporary unavailability of certain index securities in the secondary market or discrepancies between the ETF and the index with respect to the weighting of securities or the number of securities held.


Large Shareholder Transaction Risk: The Fund may experience adverse effects when certain large shareholders purchase or redeem large amounts of shares of the Fund. Such large shareholder redemptions may cause the Fund to sell its securities at times when it would not otherwise do so, which may negatively impact the Fund's NAV and liquidity. In addition, a large redemption could result in the Fund's current expenses being allocated over a smaller asset base, leading to an increase in the Fund's expense ratio. Similarly, large share purchases may adversely affect the Fund's performance to the extent that the Fund is delayed in investing new cash and is required to maintain a larger cash position than it ordinarily would.


Leverage Risks: If the Fund uses leverage through activities such as borrowing, entering into short sales, purchasing securities on margin or on a "when-issued" basis or purchasing derivative instruments in an effort to increase its returns, the Fund has the risk of magnified capital losses that occur when losses affect an asset base, enlarged by borrowings or the creation of liabilities, that exceeds the net assets of the Fund. Should the Fund employ leverage, the Fund's net asset value may be more volatile and sensitive to market movements. Leverage may involve the creation of a liability that requires the Fund to pay interest.


Liquidity Risk: Liquidity risk exists when particular investments are difficult to purchase or sell. Liquidity risk may be the result of, among other things, the reduced number and capacity of traditional market participants to make a market in fixed-income securities, or the lack of an active market. Liquid investments may become less liquid after being purchased by the Fund, particularly during periods of market stress. Illiquid and relatively less liquid investments may be harder to value, especially in turbulent markets, and if the Fund is forced to sell these investments to meet redemption requests or for other cash needs, the Fund may suffer a loss.


Market Risks: Market risk is the possibility that securities prices will fluctuate over time. This fluctuation includes both increases and decreases in security prices. The Fund is subject to market risk. The value of the Fund's investments, and the net asset value of the Fund, will fluctuate. Investors could lose money due to this price fluctuation.


Merger Arbitrage Risks: The principal risk associated with the Fund's merger arbitrage investment strategy is that the proposed reorganizations in which the Fund invests may be renegotiated or terminated, in which case the Fund may realize losses.


Options Risks: Options transactions involve special risks that may make it difficult or impossible to close a position when the Fund desires. These risks include possible imperfect correlation between the price movements of the option and the underlying security; the potential lack of a liquid secondary market at any particular time; and possible price fluctuation limits. In addition, the option activities of the Fund may affect its portfolio turnover rate and the amount of brokerage commissions paid by the Fund.


Preferred Securities Risk: Investments in preferred stocks may be subject to the risks of deferred distribution payments, subordination to debt instruments, a lack of liquidity compared to equities, limited voting rights and sensitivity to interest-rate changes.


Short Sale Risks: The Fund will suffer a loss if it sells a security short and the value of the security rises rather than falls. It is possible that the Fund's long positions will decline in value at the same time that the value of its short positions increase, thereby increasing potential losses to the Fund. Short sales expose the Fund to the risk that it will be required to buy the security sold short (also known as "covering" the short position) at a time when the security has appreciated in value, thus resulting in a loss to the Fund. The Fund's investment performance may also suffer if it is required to close out a short position earlier than it had intended. In addition, the Fund may be subject to expenses related to short sales that are not typically associated with investing in securities directly, such as costs of borrowing. These expenses may negatively impact the performance of the Fund. Short positions introduce more risk to the Fund than long positions (purchases) because the maximum sustainable loss on a security purchased (held long) is limited to the amount paid for the security plus the transaction costs, whereas there is no maximum attainable price of the shorted security. Therefore, in theory, securities sold short have unlimited risk.


Total Return Swap Risks: In a standard "swap" transaction, two parties agree to exchange the returns (or differentials in rates of return) earned or realized on particular predetermined investments or instruments. Certain categories of swap agreements often have terms of greater than seven days and may be considered illiquid. Moreover, the Fund bears the risk of loss of the amount expected to be received under a swap agreement in the event of the default or bankruptcy of a swap agreement counterparty. The swaps market is subject to extensive regulation under the Dodd-Frank Act and certain Securities and Exchange Commission and Commodity Futures Trading Commission rules promulgated thereunder. It is possible that developments in the swaps market, including new and additional government regulation, could result in higher Fund costs and expenses and could adversely affect the Fund's ability, among other things, to terminate existing swap agreements or to realize amounts to be received under such agreements.
Risk Lose Money [Text] rr_RiskLoseMoney As with all mutual funds, investing in the Fund entails risks that could cause the Fund and you to lose money.
Bar Chart and Performance Table [Heading] rr_BarChartAndPerformanceTableHeading Performance Information
Performance Narrative [Text Block] rr_PerformanceNarrativeTextBlock

The following information provides some indication of the risks and variability of investing in the Fund by showing how the Fund's performance has varied over time. The performance shown reflects the performance of the Fund's Class R shares before and after taxes and the Fund's Class I, Class C and Class A shares before taxes.


The bar chart and performance table shown below depict the performance of the Fund's Class R shares for the periods indicated and show how the Fund's average annual total returns compare with those of a broad measure of market performance. The performance table includes the performance of the Fund's Class I, Class C and Class A shares before taxes. How the Fund has performed in the past (before and after taxes) is not necessarily an indication of how the Fund will perform in the future. Performance reflects fee waivers in effect. If fee waivers were not in place, the Fund's performance would be reduced. Updated information on the Fund's performance can be obtained by visiting www.arbitragefunds.com.
Performance Information Illustrates Variability of Returns [Text] rr_PerformanceInformationIllustratesVariabilityOfReturns The following information provides some indication of the risks and variability of investing in the Fund by showing how the Fund's performance has varied over time.
Performance Availability Website Address [Text] rr_PerformanceAvailabilityWebSiteAddress www.arbitragefunds.com
Performance Past Does Not Indicate Future [Text] rr_PerformancePastDoesNotIndicateFuture How the Fund has performed in the past (before and after taxes) is not necessarily an indication of how the Fund will perform in the future.
Bar Chart [Heading] rr_BarChartHeading Year-by-Year Annual Total Returns through December 31, 2017 – Class R Shares
Bar Chart Closing [Text Block] rr_BarChartClosingTextBlock

During the period shown in the bar chart, the highest return for a quarter was 2.63% during the quarter ended September 30, 2013 and the lowest return for a quarter was -1.61% during the quarter ended September 30, 2015.


The year-to-date return of the Fund's Class R shares through June 30, 2018 is 2.15%.


While the Class I shares, Class C shares, and Class A shares would have substantially similar annual returns to the Class R shares because the shares are invested in the same portfolio of securities, the performance of Class I, Class C and Class A shares will differ from that shown above since the Classes do not have the same expenses or inception dates.
Year to Date Return, Label rr_YearToDateReturnLabel year-to-date return
Bar Chart, Year to Date Return, Date rr_BarChartYearToDateReturnDate Jun. 30, 2018
Bar Chart, Year to Date Return rr_BarChartYearToDateReturn 2.15%
Highest Quarterly Return, Label rr_HighestQuarterlyReturnLabel highest return
Highest Quarterly Return, Date rr_BarChartHighestQuarterlyReturnDate Sep. 30, 2013
Highest Quarterly Return rr_BarChartHighestQuarterlyReturn 2.63%
Lowest Quarterly Return, Label rr_LowestQuarterlyReturnLabel lowest return
Lowest Quarterly Return, Date rr_BarChartLowestQuarterlyReturnDate Sep. 30, 2015
Lowest Quarterly Return rr_BarChartLowestQuarterlyReturn (1.61%)
Performance Table Heading rr_PerformanceTableHeading Average Annual Total Returns for Periods Ended December 31, 2017
Performance Table Market Index Changed rr_PerformanceTableMarketIndexChanged Effective August 30, 2018, the Fund's primary benchmark changed from the Bloomberg Barclays U.S. Aggregate Bond Index to the ICE BofA Merrill Lynch U.S. 3-Month Treasury Bill Index. The Adviser believes that given the Fund's investment objective and strategy, the ICE BofA Merrill Lynch U.S. 3-Month Treasury Bill Index provides a more appropriate basis for comparison. The Bloomberg Barclays U.S. Aggregate Bond Index is the Fund's secondary benchmark.
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, and after-tax returns shown are not relevant to investors who hold their Fund shares through tax-deferred arrangements, such as 401(k) plans or individual retirement accounts.
Performance Table One Class of after Tax Shown [Text] rr_PerformanceTableOneClassOfAfterTaxShown After-tax returns are shown for Class R shares only, and after-tax returns for Class I, Class C, and Class A shares will vary.
Performance Table Explanation after Tax Higher rr_PerformanceTableExplanationAfterTaxHigher The Fund's return after taxes on distributions and sale of Fund shares may be higher than its returns before taxes or its returns after taxes on distributions because it may include a tax benefit resulting from the capital losses that would have been incurred.
Performance Table Narrative rr_PerformanceTableNarrativeTextBlock

The table below shows the Fund's average annual total returns for Class R shares, Class I shares, Class C shares and Class A shares compared with those of the ICE BofA Merrill Lynch U.S. 3-Month Treasury Bill Index, which is comprised of a single issue purchased at the beginning of the month, held for a full month and rolled into a newly selected issue at month-end. The issue selected at each month-end rebalancing is the outstanding Treasury Bill that matures closest to, but not beyond, three months from the rebalancing date. The table also shows performance for the Bloomberg Barclays Capital U.S. Aggregate Bond Index, a broad-based measure of the investment-grade, U.S. dollar-denominated, fixed-rate taxable bond market performance. The table also presents the impact of taxes on the returns of the Fund's Class R shares. After-tax returns are shown for Class R shares only, and after-tax returns for Class I, Class C and Class A shares will vary. 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, and after-tax returns shown are not relevant to investors who hold their Fund shares through tax-deferred arrangements, such as 401(k) plans or individual retirement accounts. Return after taxes on distributions measures the effect of taxable distributions, but assumes the underlying shares are held for the entire period. Return after taxes on distributions and sale of Fund shares shows the effect of both taxable distributions and any taxable gain or loss that would be realized if the underlying shares were purchased at the beginning and sold at the end of the period (for purposes of the calculation, it is assumed that income dividends and capital gain distributions are reinvested at net asset value and that the entire account is redeemed at the end of the period, including reinvested amounts). The Fund's return after taxes on distributions and sale of Fund shares may be higher than its returns before taxes or its returns after taxes on distributions because it may include a tax benefit resulting from the capital losses that would have been incurred.
Performance Table Closing [Text Block] rr_PerformanceTableClosingTextBlock

  In calculating the federal income taxes due on redemptions, capital gains taxes resulting from redemptions are subtracted from the redemption proceeds and the tax benefits from capital losses resulting from the redemptions are added to the redemption proceeds. Under certain circumstances, the addition of the tax benefits from capital losses resulting from redemptions may cause the Return After Taxes on Distributions and Sale of Fund Shares to be greater than the Return After Taxes on Distributions or even the Return Before Taxes.
Caption rr_AverageAnnualReturnCaption Average Annual Total Returns
THE WATER ISLAND CREDIT OPPORTUNITIES FUND | ICE BOFA MERRILL LYNCH U.S. 3-MONTH TREASURY BILL INDEX (reflects no deduction for fees, expenses, or taxes)  
Risk/Return: rr_RiskReturnAbstract  
Average Annual Returns, 1 Year rr_AverageAnnualReturnYear01 0.85% [1]
Average Annual Returns, 5 Years rr_AverageAnnualReturnYear05 0.27% [1]
Average Annual Returns, Since Inception rr_AverageAnnualReturnSinceInception 0.26% [1],[2]
Average Annual Returns, Inception Date rr_AverageAnnualReturnInceptionDate Oct. 01, 2012
THE WATER ISLAND CREDIT OPPORTUNITIES FUND | BLOOMBERG BARCLAYS CAPITAL U.S. AGGREGATE BOND INDEX (reflects no deduction for fees, expenses, or taxes)  
Risk/Return: rr_RiskReturnAbstract  
Average Annual Returns, 1 Year rr_AverageAnnualReturnYear01 3.54%
Average Annual Returns, 5 Years rr_AverageAnnualReturnYear05 2.10%
Average Annual Returns, Since Inception rr_AverageAnnualReturnSinceInception 2.04% [2]
Average Annual Returns, Inception Date rr_AverageAnnualReturnInceptionDate Oct. 01, 2012
THE WATER ISLAND CREDIT OPPORTUNITIES FUND | Class R  
Risk/Return: rr_RiskReturnAbstract  
Maximum Sales Charge (Load) Imposed on Purchases (as a percentage of offering price) rr_MaximumSalesChargeImposedOnPurchasesOverOfferingPrice none
Maximum Deferred Sales Charge (Load) (as a percentage of original purchase price) rr_MaximumDeferredSalesChargeOverOfferingPrice none
Management Fees rr_ManagementFeesOverAssets 0.95% [3]
Distribution and/or Service (12b-1) Fees rr_DistributionAndService12b1FeesOverAssets 0.25%
Dividend on Short Positions and Interest Expense on Short Positions and/or Borrowings rr_Component2OtherExpensesOverAssets 0.45%
All Remaining Other Expenses rr_Component3OtherExpensesOverAssets 0.57%
Other Expenses rr_OtherExpensesOverAssets 1.02%
Acquired Fund Fees and Expenses rr_AcquiredFundFeesAndExpensesOverAssets 0.02% [4]
Total Annual Fund Operating Expenses rr_ExpensesOverAssets 2.24% [5]
Fee Waiver rr_FeeWaiverOrReimbursementOverAssets (0.54%) [6]
Total Annual Fund Operating Expenses After Fee Waiver rr_NetExpensesOverAssets 1.70% [7]
Expense Example, with Redemption, 1 Year rr_ExpenseExampleYear01 $ 173
Expense Example, with Redemption, 3 Years rr_ExpenseExampleYear03 593
Expense Example, with Redemption, 5 Years rr_ExpenseExampleYear05 1,098
Expense Example, with Redemption, 10 Years rr_ExpenseExampleYear10 2,488
Expense Example, No Redemption, 1 Year rr_ExpenseExampleNoRedemptionYear01 173
Expense Example, No Redemption, 3 Years rr_ExpenseExampleNoRedemptionYear03 593
Expense Example, No Redemption, 5 Years rr_ExpenseExampleNoRedemptionYear05 1,098
Expense Example, No Redemption, 10 Years rr_ExpenseExampleNoRedemptionYear10 $ 2,488
Annual Return 2013 rr_AnnualReturn2013 5.65%
Annual Return 2014 rr_AnnualReturn2014 0.68%
Annual Return 2015 rr_AnnualReturn2015 (1.26%)
Annual Return 2016 rr_AnnualReturn2016 4.72%
Annual Return 2017 rr_AnnualReturn2017 1.16%
Average Annual Returns, 1 Year rr_AverageAnnualReturnYear01 1.16%
Average Annual Returns, 5 Years rr_AverageAnnualReturnYear05 2.16%
Average Annual Returns, Since Inception rr_AverageAnnualReturnSinceInception 2.08% [2]
Average Annual Returns, Inception Date rr_AverageAnnualReturnInceptionDate Oct. 01, 2012
THE WATER ISLAND CREDIT OPPORTUNITIES FUND | Class R | After Taxes on Distributions  
Risk/Return: rr_RiskReturnAbstract  
Average Annual Returns, 1 Year rr_AverageAnnualReturnYear01 0.07%
Average Annual Returns, 5 Years rr_AverageAnnualReturnYear05 0.91%
Average Annual Returns, Since Inception rr_AverageAnnualReturnSinceInception 0.87% [2]
THE WATER ISLAND CREDIT OPPORTUNITIES FUND | Class R | After Taxes on Distributions and Sale of Fund Shares  
Risk/Return: rr_RiskReturnAbstract  
Average Annual Returns, 1 Year rr_AverageAnnualReturnYear01 0.65%
Average Annual Returns, 5 Years rr_AverageAnnualReturnYear05 1.08%
Average Annual Returns, Since Inception rr_AverageAnnualReturnSinceInception 1.04% [2]
THE WATER ISLAND CREDIT OPPORTUNITIES FUND | Class I  
Risk/Return: rr_RiskReturnAbstract  
Maximum Sales Charge (Load) Imposed on Purchases (as a percentage of offering price) rr_MaximumSalesChargeImposedOnPurchasesOverOfferingPrice none
Maximum Deferred Sales Charge (Load) (as a percentage of original purchase price) rr_MaximumDeferredSalesChargeOverOfferingPrice none
Management Fees rr_ManagementFeesOverAssets 0.95% [3]
Distribution and/or Service (12b-1) Fees rr_DistributionAndService12b1FeesOverAssets none
Dividend on Short Positions and Interest Expense on Short Positions and/or Borrowings rr_Component2OtherExpensesOverAssets 0.45%
All Remaining Other Expenses rr_Component3OtherExpensesOverAssets 0.57%
Other Expenses rr_OtherExpensesOverAssets 1.02%
Acquired Fund Fees and Expenses rr_AcquiredFundFeesAndExpensesOverAssets 0.02% [4]
Total Annual Fund Operating Expenses rr_ExpensesOverAssets 1.99% [5]
Fee Waiver rr_FeeWaiverOrReimbursementOverAssets (0.54%) [6]
Total Annual Fund Operating Expenses After Fee Waiver rr_NetExpensesOverAssets 1.45% [7]
Expense Example, with Redemption, 1 Year rr_ExpenseExampleYear01 $ 148
Expense Example, with Redemption, 3 Years rr_ExpenseExampleYear03 517
Expense Example, with Redemption, 5 Years rr_ExpenseExampleYear05 970
Expense Example, with Redemption, 10 Years rr_ExpenseExampleYear10 2,227
Expense Example, No Redemption, 1 Year rr_ExpenseExampleNoRedemptionYear01 148
Expense Example, No Redemption, 3 Years rr_ExpenseExampleNoRedemptionYear03 517
Expense Example, No Redemption, 5 Years rr_ExpenseExampleNoRedemptionYear05 970
Expense Example, No Redemption, 10 Years rr_ExpenseExampleNoRedemptionYear10 $ 2,227
Average Annual Returns, 1 Year rr_AverageAnnualReturnYear01 1.44%
Average Annual Returns, 5 Years rr_AverageAnnualReturnYear05 2.40%
Average Annual Returns, Since Inception rr_AverageAnnualReturnSinceInception 2.31% [2]
Average Annual Returns, Inception Date rr_AverageAnnualReturnInceptionDate Oct. 01, 2012
THE WATER ISLAND CREDIT OPPORTUNITIES FUND | Class C  
Risk/Return: rr_RiskReturnAbstract  
Maximum Sales Charge (Load) Imposed on Purchases (as a percentage of offering price) rr_MaximumSalesChargeImposedOnPurchasesOverOfferingPrice none
Maximum Deferred Sales Charge (Load) (as a percentage of original purchase price) rr_MaximumDeferredSalesChargeOverOfferingPrice 1.00% [8]
Management Fees rr_ManagementFeesOverAssets 0.95% [3]
Distribution and/or Service (12b-1) Fees rr_DistributionAndService12b1FeesOverAssets 1.00%
Dividend on Short Positions and Interest Expense on Short Positions and/or Borrowings rr_Component2OtherExpensesOverAssets 0.45%
All Remaining Other Expenses rr_Component3OtherExpensesOverAssets 0.57%
Other Expenses rr_OtherExpensesOverAssets 1.02%
Acquired Fund Fees and Expenses rr_AcquiredFundFeesAndExpensesOverAssets 0.02% [4]
Total Annual Fund Operating Expenses rr_ExpensesOverAssets 2.99% [5]
Fee Waiver rr_FeeWaiverOrReimbursementOverAssets (0.54%) [6]
Total Annual Fund Operating Expenses After Fee Waiver rr_NetExpensesOverAssets 2.45% [7]
Expenses Deferred Charges [Text Block] rr_ExpensesDeferredChargesTextBlock This contingent deferred sales charge applies to Class C shares redeemed within 12 months of purchase.
Expense Example, with Redemption, 1 Year rr_ExpenseExampleYear01 $ 348
Expense Example, with Redemption, 3 Years rr_ExpenseExampleYear03 820
Expense Example, with Redemption, 5 Years rr_ExpenseExampleYear05 1,475
Expense Example, with Redemption, 10 Years rr_ExpenseExampleYear10 3,229
Expense Example, No Redemption, 1 Year rr_ExpenseExampleNoRedemptionYear01 248
Expense Example, No Redemption, 3 Years rr_ExpenseExampleNoRedemptionYear03 820
Expense Example, No Redemption, 5 Years rr_ExpenseExampleNoRedemptionYear05 1,475
Expense Example, No Redemption, 10 Years rr_ExpenseExampleNoRedemptionYear10 $ 3,229
Average Annual Returns, 1 Year rr_AverageAnnualReturnYear01 (0.60%)
Average Annual Returns, 5 Years rr_AverageAnnualReturnYear05 1.41%
Average Annual Returns, Since Inception rr_AverageAnnualReturnSinceInception 1.36% [2]
Average Annual Returns, Inception Date rr_AverageAnnualReturnInceptionDate Oct. 01, 2012
THE WATER ISLAND CREDIT OPPORTUNITIES FUND | Class A  
Risk/Return: rr_RiskReturnAbstract  
Maximum Sales Charge (Load) Imposed on Purchases (as a percentage of offering price) rr_MaximumSalesChargeImposedOnPurchasesOverOfferingPrice 3.25%
Maximum Deferred Sales Charge (Load) (as a percentage of original purchase price) rr_MaximumDeferredSalesChargeOverOfferingPrice 1.00% [9]
Management Fees rr_ManagementFeesOverAssets 0.95% [3]
Distribution and/or Service (12b-1) Fees rr_DistributionAndService12b1FeesOverAssets 0.25%
Dividend on Short Positions and Interest Expense on Short Positions and/or Borrowings rr_Component2OtherExpensesOverAssets 0.45%
All Remaining Other Expenses rr_Component3OtherExpensesOverAssets 0.57%
Other Expenses rr_OtherExpensesOverAssets 1.02%
Acquired Fund Fees and Expenses rr_AcquiredFundFeesAndExpensesOverAssets 0.02% [4]
Total Annual Fund Operating Expenses rr_ExpensesOverAssets 2.24% [5]
Fee Waiver rr_FeeWaiverOrReimbursementOverAssets (0.54%) [6]
Total Annual Fund Operating Expenses After Fee Waiver rr_NetExpensesOverAssets 1.70% [7]
Expenses Deferred Charges [Text Block] rr_ExpensesDeferredChargesTextBlock A deferred sales charge of up to 1.00% may be imposed on Class A shares purchased without a front-end sales charge that are redeemed within 18 months of purchase. The deferred sales charge is applicable to purchases of $500,000 or more made prior to June 30, 2018 and to purchases of $250,000 or more made after June 30, 2018 (determined on a first-in, first-out basis).
Expense Breakpoint Discounts [Text] rr_ExpenseBreakpointDiscounts You may qualify for sales charge discounts on Class A Shares if you and your family invest, or agree to invest in the future, at least $100,000 in the Fund.
Expense Breakpoint, Minimum Investment Required [Amount] rr_ExpenseBreakpointMinimumInvestmentRequiredAmount $ 100,000
Expense Example, with Redemption, 1 Year rr_ExpenseExampleYear01 492
Expense Example, with Redemption, 3 Years rr_ExpenseExampleYear03 899
Expense Example, with Redemption, 5 Years rr_ExpenseExampleYear05 1,388
Expense Example, with Redemption, 10 Years rr_ExpenseExampleYear10 2,732
Expense Example, No Redemption, 1 Year rr_ExpenseExampleNoRedemptionYear01 492
Expense Example, No Redemption, 3 Years rr_ExpenseExampleNoRedemptionYear03 899
Expense Example, No Redemption, 5 Years rr_ExpenseExampleNoRedemptionYear05 1,388
Expense Example, No Redemption, 10 Years rr_ExpenseExampleNoRedemptionYear10 $ 2,732
Average Annual Returns, 1 Year rr_AverageAnnualReturnYear01 (2.05%)
Average Annual Returns, Since Inception rr_AverageAnnualReturnSinceInception 1.15% [2]
Average Annual Returns, Inception Date rr_AverageAnnualReturnInceptionDate Jun. 01, 2013
[1] Effective August 30, 2018, the Fund's primary benchmark changed from the Bloomberg Barclays U.S. Aggregate Bond Index to the ICE BofA Merrill Lynch U.S. 3-Month Treasury Bill Index. The Adviser believes that given the Fund's investment objective and strategy, the ICE BofA Merrill Lynch U.S. 3-Month Treasury Bill Index provides a more appropriate basis for comparison. The Bloomberg Barclays U.S. Aggregate Bond Index is the Fund's secondary benchmark.
[2] The inception date for Class R shares, Class I shares and Class C shares is October 1, 2012. The inception date for the Class A shares is June 1, 2013. The "Since Inception" returns reflected for the ICE BofA Merrill Lynch U.S. 3-Month Treasury Bill Index and the Bloomberg Barclays Capital U.S. Aggregate Bond Index are based on the inception date for Class R, Class I and Class C shares.
[3] Information has been restated to reflect current fees.
[4] Acquired Fund Fees and Expenses are expenses incurred indirectly by the Fund through its ownership of shares in other investment companies.
[5] The operating expenses in this fee table do not correlate to the expense ratio in the financial highlights, but rather are restated to reflect the Fund's current (i) expense levels and (ii) expense limitation agreement.
[6] The Fund has entered into an Expense Waiver and Reimbursement Agreement with the Fund's investment adviser pursuant to which the adviser has contractually agreed to limit the total annual operating expenses of the Fund, not including taxes, interest, dividends on short positions, brokerage commissions, acquired fund fees and expenses and other costs incurred in connection with the purchase or sale of portfolio securities, so that they do not exceed 1.23% of the Fund's average daily net assets allocable to the Class R shares, 0.98% of the Fund's average daily net assets allocable to the Class I shares, 1.98% of the Fund's average daily net assets allocable to the Class C shares, and 1.23% of the Fund's average daily net assets allocable to the Class A shares. The agreement remains in effect until September 30, 2020, and thereafter renews for periods of one year until either party terminates it upon 60 days' notice prior to the end of the current initial term or then current renewal year. The Board of Trustees may terminate the agreement at any time if it determines that such termination is in the best interest of the Fund and its shareholders. The adviser may recoup any waived amount from the Fund pursuant to the agreement, if such recoupment does not cause the Fund to exceed expense limitations in effect at the time the amounts were waived and the recoupment is done within three years after the date of the expense waiver.
[7] The Total Annual Fund Operating Expenses in this fee table do not correlate to the expense ratio in the Financial Highlights because the expense ratios in the Financial Highlights do not reflect Acquired Fund Fees and Expenses.
[8] This contingent deferred sales charge applies to Class C shares redeemed within 12 months of purchase.
[9] A deferred sales charge of up to 1.00% may be imposed on Class A shares purchased without a front-end sales charge that are redeemed within 18 months of purchase. The deferred sales charge is applicable to purchases of $500,000 or more made prior to June 30, 2018 and to purchases of $250,000 or more made after June 30, 2018 (determined on a first-in, first-out basis).