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Share-based Compensation - Summary of RSU Activity (Detail) - Restricted Stock Units (RSUs) [Member] - $ / shares
shares in Thousands
12 Months Ended
Dec. 31, 2017
Dec. 31, 2016
Dec. 31, 2015
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]      
Non-vested, January 1, 2017 164    
Granted 85    
Vested 0    
Forfeited (48)    
Non-vested, at December 31, 2017 201 164  
Weighted Average Grant Date Fair Value, Non-vested, January 1, 2017 $ 16.07    
Weighted Average Grant Date Fair Value, Granted 19.99 $ 17.02 $ 14.89
Weighted Average Grant Date Fair Value, Vested 0    
Weighted Average Grant Date Fair Value, Forfeited 17.69    
Weighted Average Grant Date Fair Value, Non-vested, at December 31, 2017 $ 17.33 $ 16.07