Income Taxes - Reconciliation of Statutory Federal Income Tax to Effective Tax (Detail) - USD ($) $ in Thousands	12 Months Ended
	Jan. 31, 2018	Jan. 31, 2017	Jan. 31, 2016
Income Tax Disclosure [Abstract]
Federal tax statutory tax rate	$ 53,629	$ 38,371	$ 27,489
State taxes	3,919	3,883	2,034
Nondeductible expenses	(462)	(367)	794
Research and development credit	(9,409)	(6,739)	(4,353)
Domestic manufacturing deduction	(1,096)	(1,678)	(1,712)
Stock-based compensation	(37,347)	4,338	3,331
Foreign rate differential	(2,207)	1,042	(5,104)
Valuation allowance	4,010	1,630	5,655
Impact of foreign operations	4,842	1,891
Tax election benefit			(2,865)
Others	789	(1,540)	(1,112)
Provision for income taxes	$ 16,668	$ 40,831	$ 24,157