Income Taxes - Reconciliation of Statutory Federal Income Tax to Effective Tax (Detail) - USD ($) $ in Thousands	12 Months Ended
	Jan. 31, 2017	Jan. 31, 2016	Jan. 31, 2015
Income Tax Disclosure [Abstract]
Federal tax statutory tax rate	$ 38,371	$ 27,489	$ 23,470
State taxes	3,883	2,034	1,429
Nondeductible expenses	(367)	794	140
Research and development credit	(6,739)	(4,353)	(2,028)
Domestic manufacturing deduction	(1,678)	(1,712)	(431)
Stock-based compensation	4,338	3,331	2,506
Foreign rate differential	1,042	(5,104)	1,101
Valuation allowance	1,630	5,655	1,589
Tax election benefit		(2,865)
Others	351	(1,112)	(973)
Provision for income taxes	$ 40,831	$ 24,157	$ 26,803