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Stock-based Compensation and Outstanding Awards - Summary of Status of Nonvested Shares of RSAs and RSUs (Detail) - Restricted Stock and Restricted Stock Units [Member] - $ / shares
12 Months Ended
Dec. 31, 2017
Dec. 31, 2016
Dec. 31, 2015
Share Based Compensation Arrangement By Share Based Payment Award [Line Items]      
Nonvested shares, beginning balance 2,311,000    
Shares, Granted 580,000    
Shares, Vested (808,000)    
Shares, Forfeited (405,000)    
Nonvested shares, ending balance 1,678,000 2,311,000  
Weighted average grant date fair value, Nonvested beginning balance $ 27.66    
Weighted average grant date fair value, Granted 15.87 $ 14.71 $ 22.59
Weighted average grant date fair value, Vested 22.34    
Weighted average grant date fair value, Forfeited 28.28    
Weighted average grant date fair value, Nonvested ending balance $ 25.99 $ 27.66