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Stock-Based Compensation - Summary of Stock Based Compensation Activity (Detail)
3 Months Ended
Mar. 31, 2016
$ / shares
shares
Restricted Shares [Member]  
Share Based Compensation Arrangement By Share Based Payment Award [Line Items]  
Stock based compensation, Shares Outstanding, beginning balance | shares 2,400
Stock based compensation, Shares, Vested | shares (2,300)
Stock based compensation, Shares, Forfeited | shares (100)
Stock based compensation, Weighted Average Fair Value Per Share, beginning balance | $ / shares $ 23.42
Stock based compensation, Weighted Average Fair Value Per Share, Vested | $ / shares 23.42
Stock based compensation, Weighted Average Fair Value Per Share, Forfeited | $ / shares $ 23.42
Three Year Vest Non-Vested Restricted Stock [Member]  
Share Based Compensation Arrangement By Share Based Payment Award [Line Items]  
Stock based compensation, Shares Outstanding, beginning balance | shares 26,900
Stock based compensation, Shares, Granted | shares 21,100
Stock based compensation, Shares, Vested | shares (10,363)
Stock based compensation, Shares Outstanding, ending balance | shares 37,637
Stock based compensation, Weighted Average Fair Value Per Share, beginning balance | $ / shares $ 49.73
Stock based compensation, Weighted Average Fair Value Per Share, Granted | $ / shares 44.88
Stock based compensation, Weighted Average Fair Value Per Share, Vested | $ / shares 47.89
Stock based compensation, Weighted Average Fair Value Per Share, ending balance | $ / shares $ 47.52