Stock-Based Compensation - Summary of Status of Stock Option Activity (Detail) - USD ($) $ / shares in Units, shares in Thousands, $ in Thousands	12 Months Ended
	Dec. 31, 2017	Dec. 31, 2016	Dec. 31, 2015
Share-based Compensation Arrangement by Share-based Payment Award, Options, Outstanding [Roll Forward]
Beginning balance, (in shares)	3,941	3,967	3,607
Granted, number of shares (in shares)	263	677	659
Exercised (in shares)	(1,527)	(553)	(168)
Cancelled (in shares)	(18)	(150)	(131)
Ending balance, (in shares)	2,659	3,941	3,967
Vested and expected to vest, (in shares)	2,574
Exercisable, (in shares)	1,463
Available for future grant, (in shares)	1,848
Share-based Compensation Arrangement by Share-based Payment Award, Options, Outstanding, Weighted Average Exercise Price [Rollforward]
Beginning balance, weighted average exercise price per share (in dollars per share)	$ 17.49	$ 17.44	$ 16.37
Granted, weighted average exercise price per share (in dollars per share)	22.21	15.48	23.15
Exercised, weighted average exercise price per share (in dollars per share)	16.38	13.76	12.30
Cancelled, weighted average exercise price per share (in dollars per share)	24.91	20.86	23.41
Ending balance, weighted average exercise price per share (in dollars per share)	18.54	$ 17.49	$ 17.44
Vested and expected to vest, weighted average exercise price per share (in dollars per share)	18.51
Exercisable, weighted average exercise price per share (in dollars per share)	$ 17.71
Share-based Compensation Arrangement by Share-based Payment Award, Options, Additional Disclosures [Abstract]
Weighted- average remaining contractual term, outstanding (in years)	5 years 8 months 10 days
Weighted- average remaining contractual term, vested and expected to vest (in years)	5 years 7 months 10 days
Weighted- average remaining contractual term, exercisable (in years)	3 years 11 months 25 days
Aggregate intrinsic value, outstanding	$ 65,969
Aggregate intrinsic value, vested and expected to vest	63,914
Aggregate intrinsic value, available for future grant	$ 37,503