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Stock-Based Compensation - Summary of Stock Based Compensation Activity for Non-Qualified Stock Option Award (Detail) - Non-Qualified Stock Option Award [Member] - USD ($)
12 Months Ended
Dec. 31, 2015
Dec. 31, 2014
Dec. 31, 2013
Share Based Compensation Arrangement By Share Based Payment Award [Line Items]      
Stock based compensation, Shares Outstanding, beginning balance 84,765 94,500 60,000
Stock based compensation, Shares, Granted 70,000 10,000 51,000
Stock based compensation, Shares, Exercised (30,155) (19,735) (16,500)
Stock based compensation, Shares, Forfeited (7,760)    
Stock based compensation, Shares Outstanding, ending balance 116,850 84,765 94,500
Stock based compensation, Shares, Exercisable 28,590 37,195  
Stock based compensation, Weighted Average Exercise Price, beginning balance $ 34.39 $ 32.21 $ 28.97
Stock based compensation, Weighted Average Exercise Price, Granted 56.43 50.00 34.95
Stock based compensation, Weighted Average Exercise Price, Exercised 30.24 31.88 28.90
Stock based compensation, Weighted Average Exercise Price, Forfeited 34.95    
Stock based compensation, Weighted Average Exercise Price, ending balance 48.63 34.39 $ 32.21
Stock based compensation, Weighted Average Exercise Price, Exercisable $ 32.73 $ 30.13  
Stock based compensation, Weighted Average Remaining Contractual Term, Outstanding 7 years 4 months 13 days    
Stock based compensation, Weighted Average Remaining Contractual Term, Exercisable 4 years 4 months 28 days 6 years 15 days  
Stock based compensation, Aggregate Intrinsic Value, Outstanding $ 477,156    
Stock based compensation, Aggregate Intrinsic Value, Exercisable $ 514,193 $ 954,717