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Stock-Based Compensation Plans - Summary of Transactions of the Company's Stock Option Plans (Detail) - Stock Options Plan [Member]
9 Months Ended
Sep. 30, 2017
$ / shares
shares
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]  
Outstanding, Number of Options, Beginning balance | shares 570,994
Exercised, Number of Options | shares (83,255)
Forfeited, Number of Options | shares (3,805)
Outstanding, Number of Options, Ending balance | shares 582,441
Outstanding, Weighted Average Exercise Price, Beginning balance $ 20.38
Exercised, Weighted Average Exercise Price 12.56
Forfeited, Weighted Average Exercise Price 15.91
Outstanding, Weighted Average Exercise Price, Ending balance 20.64
Outstanding, Weighted Average Grant-Date Fair Value 21.68
Exercised 23.86
Forfeited, Weighted Average Grant-Date Fair Value 22.47
Outstanding, Weighted Average Grant-Date Fair Value $ 26.68
Discount [Member]  
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]  
Granted, Number of Options | shares 79,664
Granted, Weighted Average Exercise Price $ 0.00
Granted, Weighted Average Grant-Date Fair Value $ 61.39
Market Value [Member]  
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]  
Granted, Number of Options | shares 18,843
Granted, Weighted Average Exercise Price $ 70.60
Granted, Weighted Average Grant-Date Fair Value $ 16.84