Common Stock - Summary of Stock Option Activity (Details) - 2008 Plan - USD ($) $ / shares in Units, $ in Thousands	6 Months Ended	12 Months Ended
	Jul. 31, 2017	Jan. 31, 2017		Jan. 31, 2016
Share Based Compensation Arrangement By Share Based Payment Award [Line Items]
Number of shares underlying outstanding options, beginning balance	4,467,961	4,421,035
Number of shares underlying outstanding, Options granted	1,473,046	920,147
Number of shares underlying outstanding, Options exercised	(720,985)	(168,380)
Number of shares underlying outstanding, Options canceled	(162,495)	(704,841)
Number of shares underlying outstanding options, ending balance	5,057,527	4,467,961		4,421,035
Number of shares underlying, Options vested and exercisable	2,737,763	2,380,167
Number of shares underlying, Options vested and expected to vest	5,057,527	4,174,361	[1]
Weighted average exercise price, Outstanding beginning balance	$ 18.83	$ 16.34
Weighted average exercise price, Options granted	17.58	30.25
Weighted average exercise price, Options exercised	9.53	13.63
Weighted average exercise price, Options canceled	21.76	19.35
Weighted average exercise price, Outstanding ending balance	12.78	18.83		$ 16.34
Weighted average exercise price, Options vested and exercisable	12.03	13.55
Weighted average exercise price, Vested and Expected to Vest	$ 12.78	$ 18.54	[1]
Weighted-average remaining contractual term, Options Outstanding	8 years	7 years 6 months		8 years 2 months 12 days
Weighted-average remaining contractual term, Vested and exercisable	7 years 4 months 24 days	6 years 9 months 18 days
Weighted-average remaining contractual term, Vested and Expected to Vest	8 years	7 years 6 months	[1]
Aggregate Intrinsic Value, Options Outstanding	$ 891	$ 60,756		$ 59,882
Aggregate Intrinsic Value, Vested and exercisable	891	44,719
Aggregate Intrinsic Value, Vested and Expected to Vest	$ 891	$ 57,552	[1]

[1] The expected to vest options are a result of applying the forfeiture rate assumptions to unvested options outstanding.