Stockholders' Equity and Employee Stock Plans - Summary of Option Activity under Plans and Related Information (Detail) - USD ($) $ / shares in Units, $ in Thousands	3 Months Ended		12 Months Ended
	Mar. 31, 2018	Mar. 31, 2017	Dec. 31, 2017
Disclosure Of Compensation Related Costs Sharebased Payments [Abstract]
Number of Stock Options Outstanding, Beginning balance	997,674
Number of Stock Options Outstanding, Granted	0	0
Number of Stock Options Outstanding, Exercised	(168,408)
Number of Stock Options Outstanding, Cancelled or forfeited	(93,193)
Number of Stock Options Outstanding, Ending balance	736,073		997,674
Number of Shares, Vested and expected to vest	736,073
Number of Shares, Exercisable	640,637
Weighted Average Exercise Price of Stock Options Outstanding	$ 43.45		$ 41.87
Weighted Average Exercise Price, Exercised	31.43
Weighted Average Exercise Price, Cancelled or forfeited	48.28
Weighted Average Exercise Price, Vested and expected to vest	43.45
Weighted Average Exercise Price, Exercisable	$ 42.38
Weighted-Average Remaining Contractual Term (in years)	5 years 3 months 7 days		5 years 8 months 19 days
Weighted-Average Remaining Contractual Term (in years), Vested and expected to vest	5 years 3 months 7 days
Weighted-Average Remaining Contractual Term (in years), Exercisable	5 years
Aggregate Intrinsic Value	$ 4,823		$ 5,689
Aggregate Intrinsic Value, Vested and expected to vest	4,823
Aggregate Intrinsic Value, Exercisable	$ 4,727