Dividends on Short Positions and Interest Expense on Short Positions and/or Borrowings All Remaining Other Expenses ARBITRAGE FUND WATER ISLAND EVENT-DRIVEN FUND WATER ISLAND CREDIT OPPORTUNITIES FUND ALTSHARES MERGER ARBITRAGE ETF ALTSHARES EVENT-DRIVEN ETF ARBITRAGE FUND WATER ISLAND EVENT-DRIVEN FUND WATER ISLAND CREDIT OPPORTUNITIES FUND AltShares Merger Arbitrage ETF AltShares Event-Driven ETF Class R Class I Class C Class A Class R Class I Class A Class R Class I Class A AltShares Merger Arbitrage ETF AltShares Event-Driven ETF Merger Arbitrage Risk [Member] Passive Investment Risk [Member] Short Sale Risk [Member] Event-Driven Risk [Member] Special Situations Risk [Member] Active Management Risk [Member] Concentration Risk [Member] High Portfolio Turnover Risk [Member] Foreign Securities Risk [Member] Market Risk [Member] Sector Risk [Member] Equity Risk [Member] Derivatives Risk [Member] Convertible Security Risk [Member] Hedging Transaction Risk [Member] Counterparty Risk [Member] ETF Risk [Member] Temporary Investment/Cash Management Risk [Member] Swap Risk [Member] Options Risk [Member] Preferred Securities Risk [Member] Liquidity Risk [Member] Investment Company and ETF Risk [Member] Tracking Error Risk [Member] Large Shareholder Risk [Member] Large Shareholder Transaction Risk [Member] Leverage Risk [Member] Market Capitalization Risk [Member] Currency Risk [Member] Interest Rate Risk [Member] Credit Risk [Member] S&P 500® Index Bloomberg U.S. Treasury Bill Index Bloomberg U.S. Aggregate Bond Index S&P 500® INDEX WATER ISLAND MERGER ARBITRAGE USD HEDGED INDEX BLOOMBERG U.S. TREASURY BILL INDEX BLOOMBERG U.S. AGGREGATE BOND INDEX Tracking Error Risk Member Merger Arbitrage Risk Member index_ SP_500_ Index Member Special Situations Risk Member Options Risk Member Large Shareholder Transaction Risk Member CreditRiskMember doc_ WATER_ ISLAND_ EVENTDRIVEN_ FUNDMember C000092484 Member S000006440 Member C000279401 Member Large Shareholder Risk Member C000120978 Member ETFRisk Member Counterparty Risk Member Foreign Securities Risk Member Temporary Investment Cash Management Risk Member index_ BLOOMBERG_ US_ AGGREGATE_ BOND_ INDEXMember doc_ ARBITRAGE_ FUNDMember C000127230 Member S000030113 Member S000039281 Member Currency Risk Member S000108415 Member Derivatives Risk Member index_ Bloomberg_ US_ Treasury_ Bill_ Index Member Equity Risk Member Investment Company And ETFRisk Member Market Capitalization Risk Member doc_ ALTSHARES_ EVENTDRIVEN_ ETFMember C000017637 Member doc_ ALTSHARES_ MERGER_ ARBITRAGE_ ETFMember C000127228 Member C000279402 Member S000108414 Member C000092485 Member Convertible Security Risk Member index_ WATER_ ISLAND_ MERGER_ ARBITRAGE_ USD_ HEDGED_ INDEXMember C000115401 Member Short Sale Risk Member Passive Investment Risk Member Hedging Transaction Risk Member Sector Risk Member Swap Risk Member Active Management Risk Member Concentration Risk Member Preferred Securities Risk Member Liquidity Risk Member doc_ WATER_ ISLAND_ CREDIT_ OPPORTUNITIES_ FUNDMember Market Risk Member Leverage Risk Member C000127229 Member Event Driven Risk Member index_ Bloomberg_ US_ Aggregate_ Bond_ Index Member C000120977 Member C000017638 Member index_ SP_500_ INDEXMember InterestRateRiskMember High Portfolio Turnover Risk Member index_ BLOOMBERG_ US_ TREASURY_ BILL_ INDEXMember