Stock-based Compensation - Summary of Stock Option Activity (Detail) - USD ($) $ / shares in Units, $ in Thousands	12 Months Ended
	Dec. 31, 2017	Dec. 31, 2016	Dec. 31, 2015
Disclosure Of Compensation Related Costs Sharebased Payments [Abstract]
Shares, Beginning Balance	436,126
Granted, Shares	71,434
Exercised, Shares	(104,277)	(167,675)	(45,289)
Forfeited, Shares	(11,478)
Shares, Ending Balance	391,805	436,126
Vested or expected to vest, Shares	384,777
Exercisable, Shares	230,118
Weighted Average Exercise Price, Beginning Balance	$ 42.99
Granted, Weighted Average Exercise Price	78.56
Exercised, Weighted Average Exercise Price	32.32
Forfeited, Weighted Average Exercise Price	50.78
Weighted Average Exercise Price, Ending Balance	52.09	$ 42.99
Vested or expected to vest, Weighted Average Exercise Price	51.95
Exercisable, Weighted Average Exercise Price	$ 47.62
Weighted Average Remaining Contractual Term, Ending Balance	6 years 3 months 29 days
Vested or expected to vest, Weighted Average Remaining Contractual Term	6 years 3 months 14 days
Exercisable, Weighted Average Remaining Contractual Term	4 years 9 months 7 days
Aggregate Intrinsic Value, Ending Balance	$ 10,532
Vested or expected to vest, Aggregate Intrinsic Value	10,396
Exercisable, Aggregate Intrinsic Value	$ 7,214