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Stock Awards - Additional Information (Detail) - USD ($)
$ in Thousands
6 Months Ended
Jun. 30, 2019
Jun. 30, 2018
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]    
Share / (Unit)-based compensation expense $ 13,032 $ 6,725
Equity Incentive Plan [Member]    
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]    
Reserved shares of common stock for awards under the Equity Incentive Plan 12,900,000