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Stock-based Compensation Plans - Additional Information 2 (Detail) - USD ($)
$ / shares in Units, $ in Millions
3 Months Ended
Mar. 31, 2019
Mar. 31, 2018
Restricted Stock Equity Awards    
Share Based Compensation Arrangement By Share Based Payment Award [Line Items]    
Granted 2,792,438 1,800,000
Granted, weighted average grant date fair value $ 10.59 $ 17.00
Vesting period 3 years  
Stock-based compensation expense $ 7.1 $ 6.5
Restricted Stock Liability Awards    
Share Based Compensation Arrangement By Share Based Payment Award [Line Items]    
Granted 1,009,653  
Granted, weighted average grant date fair value $ 10.46  
Stock-based compensation expense $ 1.0 $ 8.1
Restricted Stock Liability Awards | Employees    
Share Based Compensation Arrangement By Share Based Payment Award [Line Items]    
Granted 1,000,000.0 674,000
Granted, weighted average grant date fair value $ 10.46 $ 15.21
Vesting period 3 years 3 years