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Share-based Compensation - Summary of Restricted Stock Activity (Detail) - Restricted Stock [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 39    
Granted 83    
Vested (60)    
Forfeited (9)    
Non-vested, at December 31, 2017 53 39  
Weighted Average Grant Date Fair Value, Non-vested, January 1, 2017 $ 16.46    
Weighted Average Grant Date Fair Value, Granted 18.38 $ 16.37 $ 15.36
Weighted Average Grant Date Fair Value, Vested 16.30    
Weighted Average Grant Date Fair Value, Forfeited 18.25    
Weighted Average Grant Date Fair Value, Non-vested, at December 31, 2017 $ 19.36 $ 16.46