Fair Value Measurements - Change in Fair Value of Preferred Stock Warrant Liability (Details) - USD ($) $ in Thousands	12 Months Ended
	Jan. 31, 2017	Jan. 31, 2016	Jan. 31, 2015
Fair Value Liabilities Measured On Recurring Basis Unobservable Input Reconciliation [Line Items]
Change in fair value	$ (627)	$ (190)	$ (50)
Preferred stock warrant liability
Fair Value Liabilities Measured On Recurring Basis Unobservable Input Reconciliation [Line Items]
Beginning Balance	247	332
Exercise of convertible preferred stock warrant	(874)	(275)
Change in fair value	$ 627	190
Ending Balance		$ 247	$ 332