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Stock-Based Compensation - Summary of Changes in Nonvested Restricted Stock Awards (Detail) - $ / shares
12 Months Ended
Dec. 31, 2017
Dec. 31, 2016
Dec. 31, 2015
Disclosure of Compensation Related Costs, Share-based Payments [Abstract]      
Nonvested at beginning of period, Shares 100,726    
Granted, Shares 39,673 52,750 48,300
Forfeited, Shares (2,482)    
Vested, Shares (43,445)    
Nonvested at end of period, Shares 94,472 100,726  
Nonvested at beginning of period, Weighted-average Grant Date Fair Value $ 17.36    
Granted, Weighted-average Grant Date Fair Value 25.94    
Forfeited, Weighted-average Grant Date Fair Value 21.12    
Vested, Weighted-average Grant Date Fair Value 17.54    
Nonvested at end of period, Weighted-average Grant Date Fair Value $ 20.79 $ 17.36