Income Taxes - Reconciliation of Effective Tax Rate to US Federal Statutory Rate (Detail)	12 Months Ended
	Jan. 31, 2017	Jan. 31, 2016	Jan. 31, 2015
Income Tax Disclosure [Abstract]
United States federal income tax rate	34.00%	34.00%	34.00%
State taxes, net of federal benefit	(0.60%)	0.80%	0.50%
Meals and entertainment	10.80%	(1.10%)	(1.90%)
Stock-based compensation	69.00%	(12.30%)	(20.40%)
Executive compensation	31.30%	(3.20%)	(3.40%)
United States federal and state credits	(163.50%)	26.20%	33.30%
Change in valuation allowance	406.50%	(89.50%)	(689.80%)
Change in uncertain tax positions	(46.30%)	(2.10%)
Foreign taxes and rate differential	(6.80%)	1.00%	(0.80%)
Write-off of tax attributes			(40.70%)
Other	1.90%	(1.00%)	(0.40%)
Total	336.30%	(47.20%)	(689.60%)