Fair Value Measurements - Fair Value of Financial Assets and Liabilities (Details) - Recurring - USD ($) $ in Thousands	Jan. 31, 2018	Jan. 31, 2017
Cash equivalents:
Total cash equivalents	$ 11,735	$ 31,468
Total assets measured at fair value	11,735	31,468
Convertible preferred warrants:
Total convertible preferred stock warrants		568
Total liabilities measured at fair value		568
Series E Convertible Preferred Stock Warrants
Convertible preferred warrants:
Total convertible preferred stock warrants		568
Money Market Funds
Cash equivalents:
Total cash equivalents	11,735	31,468
Level 1
Cash equivalents:
Total cash equivalents	11,735	31,468
Total assets measured at fair value	11,735	31,468
Level 1 | Money Market Funds
Cash equivalents:
Total cash equivalents	$ 11,735	31,468
Level 3
Convertible preferred warrants:
Total convertible preferred stock warrants		568
Total liabilities measured at fair value		568
Level 3 | Series E Convertible Preferred Stock Warrants
Convertible preferred warrants:
Total convertible preferred stock warrants		$ 568