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Common Stock - Summary of Non-Vested Shares of Restricted Stock (Detail) - $ / shares
12 Months Ended
Dec. 31, 2015
Dec. 31, 2014
Dec. 31, 2013
Share Based Compensation Arrangement By Share Based Payment Award [Line Items]      
Granted, Number of Shares 700,000 800,000 700,000
Granted, weighted average grant date fair value $ 22.96 $ 14.69 $ 17.21
Time-Based Restricted Stock [Member]      
Share Based Compensation Arrangement By Share Based Payment Award [Line Items]      
Nonvested balance at Dec. 31, 2014, Number of Shares 668,000    
Granted, Number of Shares 213,000    
Vested, Number of Shares (273,000)    
Forfeited, Number of Shares (19,000)    
Nonvested balance at Dec. 31, 2015, Number of Shares 589,000 668,000  
Nonvested balance at Dec. 31, 2014, Weighted Average Grant Date Fair Value $ 17.56    
Granted, weighted average grant date fair value 21.34    
Vested, Weighted Average Grant Date Fair Value 17.96    
Forfeited, Weighted Average Grant Date Fair Value 17.78    
Nonvested balance at Dec. 31, 2015, Weighted Average Grant Date Fair Value $ 18.74 $ 17.56  
Performance-Based Restricted Stock [Member]      
Share Based Compensation Arrangement By Share Based Payment Award [Line Items]      
Nonvested balance at Dec. 31, 2014, Number of Shares 1,515,000    
Granted, Number of Shares 445,000    
Vested, Number of Shares (626,000)    
Forfeited, Number of Shares (43,000)    
Nonvested balance at Dec. 31, 2015, Number of Shares 1,291,000 1,515,000  
Nonvested balance at Dec. 31, 2014, Weighted Average Grant Date Fair Value $ 15.44    
Granted, weighted average grant date fair value 23.72    
Vested, Weighted Average Grant Date Fair Value 15.94    
Forfeited, Weighted Average Grant Date Fair Value 16.05    
Nonvested balance at Dec. 31, 2015, Weighted Average Grant Date Fair Value $ 18.06 $ 15.44