Stock-Based Compensation Plans - Summary of Stock Options Issued Pursuant to Stock Incentive Plans (Detail)	6 Months Ended
	Jun. 30, 2018 USD ($) $ / shares shares
Number of Shares
Outstanding, Beginning Balance | shares	6,162,717
Granted | shares	170,455
Exercised | shares	(1,050,518)
Forfeited | shares	(52,827)
Outstanding, Ending Balance | shares	5,229,827
Number of Shares Exercisable, Ending Balance | shares	3,688,160
Weighted-Average Exercise Price
Beginning Balance | $ / shares	$ 16.83
Granted | $ / shares	23.36
Exercised | $ / shares	14.19
Forfeited | $ / shares	19.02
Ending Balance | $ / shares	17.55
Weighted-Average Exercise Price Exercisable, Ending Balance | $ / shares	$ 16.78
Weighted-Average Remaining Contractual Term (Years)
Weighted Average Remaining Contractual Term (Years), Outstanding as of end of period	6 years 4 months 24 days
Weighted-Average Remaining Contractual Term (Years), Exercisable as of end of period	5 years 8 months 8 days
Aggregate Intrinsic Value of In-the-Money Options
Aggregate Intrinsic Value of In-the-Money Options, Outstanding as of end of period | $	$ 37,215,726
Aggregate Intrinsic Value of In-the-Money Options, Exercisable as of end of period | $	$ 29,089,836