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Stock-Based Compensation - Additional Information (Detail)
$ in Millions
3 Months Ended
Mar. 31, 2018
USD ($)
shares
Restricted stock [Member]  
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]  
Stock available to grant | shares 13,701,105
Fair value at vesting date | $ $ 52.5
Unrecognized compensation expense related to non-vested | $ $ 104.0
Unrecognized compensation expense related to non-vested, period for recognition, in years 1 year 8 months 17 days
Restricted stock [Member] | Minimum [Member]  
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]  
Grants vest over periods, in years 1 year
Restricted stock [Member] | Maximum [Member]  
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]  
Grants vest over periods, in years 3 years
2013 Plan [Member]  
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]  
Common stock available for issue | shares 19,680,072