Stock-Based Compensation - Summary of Activity under Stock Plans (Detail) - USD ($) $ / shares in Units, $ in Thousands	12 Months Ended
	Dec. 31, 2018	Dec. 31, 2017	Dec. 31, 2016	Dec. 31, 2015
Sharebased Compensation Arrangement By Sharebased Payment Award Options Outstanding Weighted Average Exercise Price And Additional Disclosures [Abstract]
Number of Options, Outstanding Beginning balances	2,559,972	2,821,227	3,050,288
Number of Options, Options granted	236,900	503,690	498,564
Number of Options, Options exercised	(247,768)	(707,410)	(667,494)
Number of Options, Options cancelled	(19,364)	(57,535)	(60,131)
Number of Options, Outstanding Ending balances	2,529,740	2,559,972	2,821,227	3,050,288
Number of Options, Options exercisable	2,478,361
Number of Options, Options vested, exercisable or expected to vest	1,700,383
Weighted Average Exercise Price, Beginning balances	$ 43.62	$ 29.85	$ 19.74
Weighted Average Exercise Price, Options granted	47.96	74.71	66.74
Weighted Average Exercise Price, Options exercised	16.05	10.59	10.19
Weighted Average Exercise Price, Options cancelled	44.70	46.83	40.89
Weighted Average Exercise Price, Ending balances	46.72	$ 43.62	$ 29.85	$ 19.74
Weighted Average Exercise Price, Options exercisable	46.40
Weighted Average Exercise Price, Options vested, exercisable or expected to vest	$ 38.33
Options Outstanding, Weighted-Average Remaining Contractual Term	6 years 8 months 12 days	7 years 3 months 18 days	7 years 4 months 24 days	7 years 9 months 18 days
Options exercisable, Weighted-Average Remaining Contractual Term	6 years 8 months 12 days
Options vested, exercisable or expected to vest, Weighted Average Remaining Contractual Term	5 years 9 months 18 days
Options Outstanding, Aggregate Intrinsic Value	$ 21,866	$ 71,120	$ 123,425	$ 145,721
Options exercised, Aggregate Intrinsic Value	15,468	$ 50,971	$ 46,529
Options exercisable, Aggregate Intrinsic Value	21,866
Options vested, exercisable or expected to vest, Aggregate Intrinsic Value	$ 21,866