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Stock-based Compensation and Other Employee Benefits- Vested RSUs - Additional Information (Detail) - USD ($)
12 Months Ended
Dec. 31, 2018
Dec. 31, 2017
Dec. 31, 2016
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]      
Options granted (in shares) 0    
Employee Service Share-based Compensation, Nonvested Awards, Compensation Cost Not yet Recognized, Period for Recognition 1 year 9 months 18 days    
RSUs      
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]      
Fair value of RSUs vested during the year $ 35.63 $ 42.74 $ 38.34
Aggregate intrinsic value of RSUs vested and expected to vest $ 70,700,000    
Number of RSUs vested and expected to vest 2,900,000    
Unrecognized compensation expense other than options $ 35,400,000    
Employee Service Share-based Compensation, Nonvested Awards, Compensation Cost Not yet Recognized, Period for Recognition 1 year    
Stock Options      
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]      
Non-vested performance-based RSUs 21.00%    
Options granted (in shares) 0 0 0