Fair Value Measurements - Summary of Changes in Fair Value of Convertible Preferred Stock Warrant Liability (Details) - USD ($) $ in Thousands	9 Months Ended	12 Months Ended
	Oct. 31, 2017	Jan. 31, 2017
Fair Value Disclosures [Abstract]
Convertible preferred stock warrant liability—beginning balance	$ 568	$ 532
Change in fair value	(470)	36
Issuance of convertible preferred stock warrants	277
Reclassification of convertible preferred stock warrant liability to additional paid in capital	$ (375)
Convertible preferred stock warrant liability—ending balance		$ 568