v3.26.3
Average Annual Total Returns
 12 Months Ended 60 Months Ended 68 Months Ended 120 Months Ended 151 Months Ended 159 Months Ended 163 Months Ended 183 Months Ended 266 Months Ended 303 Months Ended
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Dec. 31, 2025
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 [12]
Dec. 31, 2025
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Dec. 31, 2025
 [9]
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 [1]
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ARBITRAGE FUND | Class R                      
Prospectus [Line Items]                      
Average Annual Return, Percent   8.01% 3.23%   3.32%           3.87%
Performance Inception Date Sep. 18, 2000                    
ARBITRAGE FUND | Class R | After Taxes on Distributions                      
Prospectus [Line Items]                      
Average Annual Return, Percent   6.98% 2.57%   2.43%           2.94%
ARBITRAGE FUND | Class R | After Taxes on Distributions and Sales                      
Prospectus [Line Items]                      
Average Annual Return, Percent   5.24% 2.32%   2.27%           2.75%
ARBITRAGE FUND | Class I                      
Prospectus [Line Items]                      
Average Annual Return, Percent   8.29% 3.48%   3.57%         3.27%  
Performance Inception Date Oct. 17, 2003                    
ARBITRAGE FUND | Class C                      
Prospectus [Line Items]                      
Average Annual Return, Percent   6.25% 2.47%   2.55%     1.95%      
Performance Inception Date Jun. 01, 2012                    
ARBITRAGE FUND | Class A                      
Prospectus [Line Items]                      
Average Annual Return, Percent   5.05% 2.65%   3.05% 2.69% [1]          
Performance Inception Date Jun. 01, 2013                    
ARBITRAGE FUND | S&P 500® Index                      
Prospectus [Line Items]                      
Average Annual Return, Percent [2]   17.88% 14.42%   14.82%           8.29%
ARBITRAGE FUND | Bloomberg U.S. Treasury Bill Index                      
Prospectus [Line Items]                      
Average Annual Return, Percent [3]   4.30% 3.19%   2.20%           1.92%
ARBITRAGE FUND | Bloomberg U.S. Aggregate Bond Index                      
Prospectus [Line Items]                      
Average Annual Return, Percent [4]   7.30% (0.36%)   2.01%           3.92%
WATER ISLAND EVENT-DRIVEN FUND | Class R                      
Prospectus [Line Items]                      
Average Annual Return, Percent   8.41% 3.16%   4.12%       2.78%    
Performance Inception Date Oct. 01, 2010                    
WATER ISLAND EVENT-DRIVEN FUND | Class R | After Taxes on Distributions                      
Prospectus [Line Items]                      
Average Annual Return, Percent   8.23% 3.08%   4.01%       2.33%    
WATER ISLAND EVENT-DRIVEN FUND | Class R | After Taxes on Distributions and Sales                      
Prospectus [Line Items]                      
Average Annual Return, Percent   5.10% 2.42%   3.23%       1.99%    
WATER ISLAND EVENT-DRIVEN FUND | Class I                      
Prospectus [Line Items]                      
Average Annual Return, Percent   8.67% 3.42%   4.39%       3.04%    
Performance Inception Date Oct. 01, 2010                    
WATER ISLAND EVENT-DRIVEN FUND | Class A                      
Prospectus [Line Items]                      
Average Annual Return, Percent   4.93% 2.49%   3.80% 2.48% [5]          
Performance Inception Date Jun. 01, 2013                    
WATER ISLAND EVENT-DRIVEN FUND | S&P 500® Index                      
Prospectus [Line Items]                      
Average Annual Return, Percent [6]   17.88% 14.42%   14.82%       14.58%    
WATER ISLAND EVENT-DRIVEN FUND | Bloomberg U.S. Treasury Bill Index                      
Prospectus [Line Items]                      
Average Annual Return, Percent [7]   4.30% 3.19%   2.20%       1.48%    
WATER ISLAND EVENT-DRIVEN FUND | Bloomberg U.S. Aggregate Bond Index                      
Prospectus [Line Items]                      
Average Annual Return, Percent [8]   7.30% (0.36%)   2.01%       2.29%    
WATER ISLAND CREDIT OPPORTUNITIES FUND | Class R                      
Prospectus [Line Items]                      
Average Annual Return, Percent   4.62% 3.34%   3.59%   3.09%        
Performance Inception Date Oct. 01, 2012                    
WATER ISLAND CREDIT OPPORTUNITIES FUND | Class R | After Taxes on Distributions                      
Prospectus [Line Items]                      
Average Annual Return, Percent   2.97% 1.79%   2.24%   1.75%        
WATER ISLAND CREDIT OPPORTUNITIES FUND | Class R | After Taxes on Distributions and Sales                      
Prospectus [Line Items]                      
Average Annual Return, Percent   2.72% 1.88%   2.17%   1.77%        
WATER ISLAND CREDIT OPPORTUNITIES FUND | Class I                      
Prospectus [Line Items]                      
Average Annual Return, Percent   4.79% 3.58%   3.84%   3.33%        
Performance Inception Date Oct. 01, 2012                    
WATER ISLAND CREDIT OPPORTUNITIES FUND | Class A                      
Prospectus [Line Items]                      
Average Annual Return, Percent   1.11% 2.64%   3.23% 2.78% [9]          
Performance Inception Date Jun. 01, 2013                    
WATER ISLAND CREDIT OPPORTUNITIES FUND | Bloomberg U.S. Treasury Bill Index                      
Prospectus [Line Items]                      
Average Annual Return, Percent [10]   4.30% 3.19%   2.20%   1.68%        
WATER ISLAND CREDIT OPPORTUNITIES FUND | Bloomberg U.S. Aggregate Bond Index                      
Prospectus [Line Items]                      
Average Annual Return, Percent [11]   7.30% (0.36%)   2.01%   1.86%        
ALTSHARES MERGER ARBITRAGE ETF | AltShares Merger Arbitrage ETF                      
Prospectus [Line Items]                      
Average Annual Return, Percent   5.58% 3.88% 4.18%              
Performance Inception Date May 07, 2020                    
ALTSHARES MERGER ARBITRAGE ETF | AltShares Merger Arbitrage ETF | After Taxes on Distributions                      
Prospectus [Line Items]                      
Average Annual Return, Percent   5.46% 3.45% 3.59%              
ALTSHARES MERGER ARBITRAGE ETF | AltShares Merger Arbitrage ETF | After Taxes on Distributions and Sales                      
Prospectus [Line Items]                      
Average Annual Return, Percent   3.37% 2.83% 3.00%              
ALTSHARES MERGER ARBITRAGE ETF | S&P 500® INDEX                      
Prospectus [Line Items]                      
Average Annual Return, Percent [13]   17.88% 14.42% 18.55%              
ALTSHARES MERGER ARBITRAGE ETF | WATER ISLAND MERGER ARBITRAGE USD HEDGED INDEX                      
Prospectus [Line Items]                      
Average Annual Return, Percent [14]   6.87% 5.22% 5.54%              
ALTSHARES MERGER ARBITRAGE ETF | BLOOMBERG U.S. TREASURY BILL INDEX                      
Prospectus [Line Items]                      
Average Annual Return, Percent [15]   4.30% 3.19% 2.83%              
ALTSHARES MERGER ARBITRAGE ETF | BLOOMBERG U.S. AGGREGATE BOND INDEX                      
Prospectus [Line Items]                      
Average Annual Return, Percent [16]   7.30% (0.36%) 0.19%              
ALTSHARES EVENT-DRIVEN ETF | AltShares Event-Driven ETF                      
Prospectus [Line Items]                      
Average Annual Return, Percent 5.51% 13.57% 3.78%                
ALTSHARES EVENT-DRIVEN ETF | AltShares Event-Driven ETF | After Taxes on Distributions                      
Prospectus [Line Items]                      
Average Annual Return, Percent 3.95% 11.57% 1.52%                
ALTSHARES EVENT-DRIVEN ETF | AltShares Event-Driven ETF | After Taxes on Distributions and Sales                      
Prospectus [Line Items]                      
Average Annual Return, Percent 3.68% 8.16% 1.90%                
ALTSHARES EVENT-DRIVEN ETF | S&P 500® INDEX                      
Prospectus [Line Items]                      
Average Annual Return, Percent [17] 13.42% 17.88% 14.42%                
ALTSHARES EVENT-DRIVEN ETF | BLOOMBERG U.S. TREASURY BILL INDEX                      
Prospectus [Line Items]                      
Average Annual Return, Percent [18] 2.01% 4.30% 3.19%                
ALTSHARES EVENT-DRIVEN ETF | BLOOMBERG U.S. AGGREGATE BOND INDEX                      
Prospectus [Line Items]                      
Average Annual Return, Percent [19] 1.88% 7.30% (0.36%)                
[1] The inception date for Class R shares is September 18, 2000, the inception date for Class I shares is October 17, 2003, the inception date for Class C shares is June 1, 2012, and the inception date for the Class A shares is June 1, 2013. The “Since Inception” returns reflected for the S&P 500® Index, the Bloomberg U.S. Treasury Bill Index and the Bloomberg U.S. Aggregate Bond Index are based on the inception date for Class R shares.
[2] To meet regulatory requirements, the S&P 500® Index serves as the Fund’s broad-based securities market index, providing a broad measure of market performance. The S&P 500® Index, or simply the S&P 500, is a stock market index tracking the performance of 500 large companies listed on stock exchanges in the U.S.
[3] The Bloomberg U.S. Treasury Bill Index tracks the market for treasury bills issued by the US government with at least one month and up to, but not including, twelve months remaining to maturity.
[4] The Bloomberg U.S. Aggregate Bond Index is a market value-weighted index of investment grade fixed-rated debt issues, including government, corporate, asset-backed and mortgage-backed securities with a maturity of one year or more.
[5] The inception date for Class R shares and Class I shares is October 1, 2010 and the inception date for the Class A shares is June 1, 2013. The “Since Inception” returns reflected for the S&P 500® Index, the Bloomberg U.S. Treasury Bill Index and the Bloomberg U.S. Aggregate Bond Index are based on the inception date for Class R shares.
[6] To meet regulatory requirements, the S&P 500® Index serves as the Fund’s broad-based securities market index, providing a broad measure of market performance. The S&P 500® Index, or simply the S&P 500, is a stock market index tracking the performance of 500 large companies listed on stock exchanges in the U.S.
[7] The Bloomberg U.S. Treasury Bill Index tracks the market for treasury bills issued by the US government with at least one month and up to, but not including, twelve months remaining to maturity.
[8] The Bloomberg U.S. Aggregate Bond Index is a market value-weighted index of investment grade fixed-rated debt issues, including government, corporate, asset-backed and mortgage-backed securities with a maturity of one year or more.
[9] The inception date for Class R shares and Class I shares is October 1, 2012. The inception date for the Class A shares is June 1, 2013. The “Since Inception” returns reflected for the Bloomberg U.S. Aggregate Bond Index and the Bloomberg U.S. Treasury Bill Index are based on the inception date for Class R and Class I shares.
[10] Bloomberg U.S. Treasury Bill Index tracks the market for treasury bills issued by the US government with at least one month and up to, but not including, twelve months remaining to maturity.
[11] To meet regulatory requirements, the Bloomberg U.S. Aggregate Bond Index serves as the Fund’s broad-based securities market index, providing a broad measure of market performance. The Bloomberg U.S. Aggregate Bond Index is a market value-weighted index of investment grade fixed-rated debt issues, including government, corporate, asset-backed and mortgage-backed securities with a maturity of one year or more.
[12] The predecessor exchange traded fund’s inception date is May 7, 2020.
[13] To meet regulatory requirements, the S&P 500® Index serves as the Fund’s broad-based securities market index, providing a broad measure of market performance. The S&P 500® Index, or simply the S&P 500, is a stock market index tracking the performance of 500 large companies listed on stock exchanges in the U.S.
[14] The Water Island Merger Arbitrage USD Hedged Index is the Fund’s Underlying Index and is most representative of the Fund’s risk and return and investment style. The Fund seeks to provide investment results that closely correspond, before fees and expenses, to the performance of its Underlying Index. The Water Island Merger Arbitrage USD Hedged Index is designed to reflect a global merger arbitrage strategy investing in definitive, publicly announced mergers and acquisitions and is comprised of securities of U.S. and foreign companies of any market capitalization.
[15] The Bloomberg U.S. Treasury Bill Index tracks the market for treasury bills issued by the US government with at least one month and up to, but not including, twelve months remaining to maturity.
[16] The Bloomberg U.S. Aggregate Bond Index is a market value-weighted index of investment grade fixed-rated debt issues, including government, corporate, asset-backed and mortgage-backed securities with a maturity of one year or more.
[17] The S&P 500® Index serves as the Fund’s regulatory index and provides a broad measure of market performance. The Standard and Poor’s 500® Index, or simply the S&P 500, is a stock market index tracking the performance of 500 large companies listed on stock exchanges in the U.S.
[18] The Bloomberg U.S. Treasury Bill Index tracks the market for treasury bills issued by the US government with at least one month and up to, but not including, twelve months remaining to maturity.
[19] The Bloomberg U.S. Aggregate Bond Index is one of the Fund’s additional indexes and is also more representative of the Fund’s risk and return than the regulatory index. The Bloomberg U.S. Aggregate Bond Index is a market value-weighted index of investment grade fixed-rated debt issues, including government, corporate, asset-backed and mortgage-backed securities with a maturity of one year or more.