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Stock-Based Compensation - Summary of Restricted Stock Unit Activity (Detail) - Restricted stock units - $ / shares
12 Months Ended
Dec. 31, 2018
Dec. 31, 2017
Dec. 31, 2016
Share-based Compensation Arrangement by Share-based Payment Award, Equity Instruments Other than Options, Nonvested, Number of Shares [Roll Forward]      
Restricted stock units outstanding at December 31, 2017 2,185,466    
Granted 374,810    
Released (339,972)    
Forfeited (18,080)    
Restricted stock units outstanding at December 31, 2018 2,202,224 2,185,466  
Weighted average grant date fair value      
Restricted stock units outstanding at December 31, 2017 $ 25.81    
Granted 28.51 $ 29.94 $ 25.77
Released 26.38    
Forfeited 28.18    
Restricted stock units outstanding at December 31, 2018 $ 26.16 $ 25.81