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Stock-based Compensation Plans - Restricted Stock and Restricted Stock Units Outstanding (Detail) - $ / shares
12 Months Ended
Dec. 31, 2020
Dec. 31, 2019
Dec. 31, 2018
Restricted Stock Equity Awards      
Share Based Compensation Arrangement By Share Based Payment Award [Line Items]      
Outstanding, Beginning Balance 2,002,239    
Granted 4,462,711 2,800,000 1,800,000
Vested (3,063,652)    
Forfeited (585,438)    
Outstanding, Ending Balance 2,815,860 2,002,239  
Outstanding, Beginning Balance, weighted average grant date fair value $ 12.32    
Granted, weighted average grant date fair value 3.42    
Vested, weighted average grant date fair value 6.93    
Forfeited, weighted average grant date fair value 8.03    
Outstanding, Ending Balance, weighted average grant date fair value $ 4.97 $ 12.32  
Restricted Stock Liability Awards      
Share Based Compensation Arrangement By Share Based Payment Award [Line Items]      
Outstanding, Beginning Balance 411,126    
Granted 3,535,093 1,200,000 891,000
Vested (2,678,013)    
Forfeited (81,570)    
Outstanding, Ending Balance 1,186,636 411,126  
Outstanding, Beginning Balance, weighted average grant date fair value $ 10.94    
Granted, weighted average grant date fair value 3.18 $ 10.16 $ 15.30
Vested, weighted average grant date fair value 3.94    
Forfeited, weighted average grant date fair value 3.02    
Outstanding, Ending Balance, weighted average grant date fair value $ 4.18 $ 10.94