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Share-Based Compensation - Summary of Status of Non-vested, Restricted and Performance Shares (Detail) - Restricted and Performance Shares [Member]
12 Months Ended
Dec. 31, 2017
$ / shares
shares
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]  
Non-vested beginning of year, Shares | shares 70,959
Vested, Shares | shares (6,754)
Granted, Shares | shares 41,786
Forfeited, Shares | shares (9,461)
Non-vested, end of year, Shares | shares 96,530
Non-vested beginning of year, Weighted Average Grant Date Fair Value | $ / shares $ 15.59
Vested, Weighted Average Grant Date Fair Value | $ / shares 14.80
Granted, Weighted Average Grant Date Fair Value | $ / shares 25.49
Forfeited, Weighted Average Grant Date Fair Value | $ / shares 15.05
Non-vested end of year, Weighted Average Grant Date Fair Value | $ / shares $ 19.98