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Commitments and Contingencies - Additional Information (Detail) - USD ($)
2 Months Ended 3 Months Ended 12 Months Ended
Mar. 31, 2016
Mar. 31, 2016
Mar. 31, 2015
Dec. 31, 2017
Dec. 31, 2015
Jan. 15, 2016
Jun. 26, 2015
Commitment And Contingencies [Line Items]              
Operating lease agreements expiration date   Various dates through 2025          
Rental expense relating to operating leases   $ 7,985,000 $ 8,871,000        
Unfunded commitments for capital contributions $ 5,610,000 5,610,000          
Investment in private equity funds 83,669,000 83,669,000     $ 86,287,000    
Other Commitment     5,500,000        
Loans and Leases Receivable, Gross     $ 3,500,000        
Remaining Loan Commitment 2,000,000 $ 2,000,000          
Loss Contingency, Damages Sought, Value         300,000,000    
Protego [Member]              
Commitment And Contingencies [Line Items]              
Percentage of the return proceeds received payable (as a percent)   90.00%          
Private Equity Funds [Member]              
Commitment And Contingencies [Line Items]              
Investment in private equity funds 27,578,000 $ 27,578,000     26,473,000    
Private Equity Funds [Member] | Discovery Fund [Member]              
Commitment And Contingencies [Line Items]              
Investment in private equity funds 6,928,000 6,928,000     $ 6,632,000    
Private Equity Funds [Member] | Discovery Fund [Member] | Protego [Member]              
Commitment And Contingencies [Line Items]              
Goodwill 4,722,000 4,722,000          
Investment in private equity funds 6,928,000 $ 6,928,000          
Scenario, Forecast [Member]              
Commitment And Contingencies [Line Items]              
Subsidiary or Equity Method Investee, Cumulative Percentage Ownership after All Transactions       20.00%      
First Republic Bank [Member]              
Commitment And Contingencies [Line Items]              
Maximum borrowing capacity           $ 50,000,000 $ 75,000,000
Line of Credit Facility, Expiration Date   Jun. 27, 2016          
Amount outstanding during period $ 50,000,000