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Stock Awards - Additional Information (Detail)
$ in Thousands
9 Months Ended
Sep. 30, 2017
USD ($)
board_member
shares
Sep. 30, 2016
USD ($)
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]    
Share / (Unit)-based compensation expense | $ $ 7,148 $ 5,832
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 | shares 8,196,770  
Common stock remaining for future stock awards transferred to the equity incentive plan | shares 3,300,000  
Time Based Stock Options [Member]    
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]    
Share based compensation acceleration of vestings | $ $ 400  
Number of former board member | board_member 3