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Stock-Based Compensation Plans - Summary of Transactions of the Company's Stock Option Plans (Detail) - Stock Options Plan [Member]
6 Months Ended
Jun. 30, 2018
$ / shares
shares
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]  
Outstanding, Number of Options, Beginning balance | shares 357,666
Exercised, Number of Options | shares (83,512)
Forfeited, Number of Options | shares (14,043)
Outstanding, Number of Options, Ending balance | shares 350,188
Outstanding, Weighted Average Exercise Price, Beginning balance $ 13.74
Exercised, Weighted Average Exercise Price 13.24
Forfeited, Weighted Average Exercise Price 21.65
Outstanding, Weighted Average Exercise Price, Ending balance 13.68
Outstanding, Weighted Average Grant-Date Fair Value 35.69
Exercised 25.93
Forfeited, Weighted Average Grant-Date Fair Value 24.84
Outstanding, Weighted Average Grant-Date Fair Value $ 41.84
Discount [Member]  
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]  
Granted, Number of Options | shares 71,227
Granted, Weighted Average Exercise Price $ 0.00
Granted, Weighted Average Grant-Date Fair Value $ 57.53
Market Value [Member]  
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]  
Granted, Number of Options | shares 18,850
Granted, Weighted Average Exercise Price $ 68.20
Granted, Weighted Average Grant-Date Fair Value $ 16.23