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Retirement Savings Plan - Additional Information (Detail) - USD ($)
$ in Thousands
12 Months Ended
Dec. 31, 2018
Dec. 31, 2017
Dec. 31, 2016
Defined Contribution Plan Disclosure [Line Items]      
Maximum allowable contribution by employee percentage 100.00%    
Defined benefit plan employer matching contribution percent 50.00%    
Maximum annual contribution per employee, percent 6.00%    
Employer matching contribution amount $ 2,900 $ 1,600 $ 1,400
Stock-based compensation expense 12,510 $ 12,727 $ 8,023
401(k) Stock Match [Member]      
Defined Contribution Plan Disclosure [Line Items]      
Stock-based compensation expense $ 1,238