Stock-Based Compensation Plans - Summary of Stock Options Issued Pursuant to Stock Incentive Plans (Detail)	3 Months Ended
	Mar. 31, 2018 USD ($) $ / shares shares
Number of Shares
Outstanding, Beginning Balance | shares	6,162,717
Granted | shares	170,455
Exercised | shares	(656,898)
Forfeited | shares	(3,255)
Outstanding, Ending Balance | shares	5,673,019
Number of Shares Exercisable, Ending Balance | shares	4,081,780
Weighted-Average Exercise Price
Beginning Balance | $ / shares	$ 16.83
Granted | $ / shares	23.36
Exercised | $ / shares	13.88
Forfeited | $ / shares	17.89
Ending Balance | $ / shares	17.37
Weighted-Average Exercise Price Exercisable, Ending Balance | $ / shares	$ 16.58
Weighted-Average Remaining Contractual Term (Years)
Weighted Average Remaining Contractual Term (Years), Outstanding as of end of period	6 years 8 months 26 days
Weighted-Average Remaining Contractual Term (Years), Exercisable as of end of period	6 years 1 month 9 days
Aggregate Intrinsic Value of In-the-Money Options
Aggregate Intrinsic Value of In-the-Money Options, Outstanding as of end of period | $	$ 36,025,874
Aggregate Intrinsic Value of In-the-Money Options, Exercisable as of end of period | $	$ 29,135,028