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Employee Benefit Plan - Additional Information (Detail) - USD ($)
12 Months Ended
Dec. 31, 2018
Dec. 31, 2017
Dec. 31, 2016
Retirement Benefits [Abstract]      
Maximum employee contribution to defined contribution benefit plans 75.00%    
Employer matching contribution, percentage 50.00%    
Employer matching contribution, percentage of employees' gross pay 6.00%    
Discretionary contributions by employer   $ 0 $ 0
Defined contribution plan employee vesting percentage 100.00%    
Defined contribution plan employer vesting percentage 50.00%    
Number of years of service required to vest in full 2 years    
Employer contribution towards compensation plan $ 2,340,000 $ 1,927,000 $ 1,842,000