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Retirement Plan - Additional Information (Detail) - USD ($)
$ in Millions
12 Months Ended
Dec. 31, 2018
Dec. 31, 2017
Dec. 31, 2016
Compensation And Retirement Disclosure [Abstract]      
Defined contribution plan, maximum employee contribution percentage 60.00%    
Defined contribution plan, employer contribution amount $ 1.8 $ 1.1 $ 0.6