Fair Value Measurements - Fair Value of Financial Assets and Liabilities (Details) - USD ($) $ in Thousands	Oct. 31, 2017	Jan. 31, 2017
Short-term investments:
Total short-term investments	$ 5,994	$ 0
Recurring
Cash equivalents:
Total cash equivalents	31,685	31,468
Total assets measured at fair value	37,679	31,468
Convertible preferred warrants:
Total convertible preferred stock warrants		568
Total liabilities measured at fair value		568
Short-term investments:
Total short-term investments	5,994
Recurring | Corporate Debt Securities
Short-term investments:
Total short-term investments	5,994
Recurring | Series E Convertible Preferred Stock Warrants
Convertible preferred warrants:
Total convertible preferred stock warrants		568
Recurring | Money Market Funds
Cash equivalents:
Total cash equivalents	31,685	31,468
Recurring | Level 1
Cash equivalents:
Total cash equivalents	31,685	31,468
Total assets measured at fair value	31,685	31,468
Recurring | Level 1 | Money Market Funds
Cash equivalents:
Total cash equivalents	31,685	31,468
Recurring | Level 2
Cash equivalents:
Total assets measured at fair value	5,994
Short-term investments:
Total short-term investments	5,994
Recurring | Level 2 | Corporate Debt Securities
Short-term investments:
Total short-term investments	$ 5,994
Recurring | Level 3
Convertible preferred warrants:
Total convertible preferred stock warrants		568
Total liabilities measured at fair value		568
Recurring | Level 3 | Series E Convertible Preferred Stock Warrants
Convertible preferred warrants:
Total convertible preferred stock warrants		$ 568