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Stock-Based Compensation - Summary of Nonvested Common Stock (Detail) - Common Stock Awards [Member] - Deferred Compensation Plan [Member] - $ / shares
shares in Thousands
12 Months Ended
Dec. 31, 2015
Dec. 31, 2014
Dec. 31, 2013
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]      
Nonvested Shares, beginning balance 5    
Granted, Shares 8 10 13
Vested, Shares (10)    
Forfeited, Shares 0    
Nonvested Shares, ending balance 3 5  
Nonvested, Weighted Average Grant-Date Fair Value, beginning balance $ 17.88    
Granted, Weighted Average Grant-Date Fair Value 25.06 $ 20.54 $ 16.76
Vested, Weighted Average Grant-Date Fair Value 23.12    
Forfeited or expired, Weighted Average Grant-Date Fair Value 0    
Nonvested, Weighted Average Grant-Date Fair Value, ending balance $ 19.53 $ 17.88