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Stock-Based Compensation - Summary of Activity for RSUs (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]      
Non-vested RSUs - end of period 733,000    
Weighted Average Grant Date Fair Value, Granted $ 8.16 $ 6.37 $ 5.76
Restricted Stock Units (RSUs) [Member]      
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]      
Non-vested RSUs - beginning of period 716,714    
Granted 394,952    
Vested (351,601)    
Forfeited or expired (26,903)    
Non-vested RSUs - end of period 733,162 716,714  
Weighted Average Grant Date Fair Value, Beginning of period $ 28.67    
Weighted Average Grant Date Fair Value, Granted 32.89    
Weighted Average Grant Date Fair Value, Vested 28.59    
Weighted Average Grant Date Fair Value, Forfeited or expired 29.84    
Weighted Average Grant Date Fair Value, end of period $ 30.94 $ 28.67