Fair Value Measurements - Fair Value of Financial Assets and Liabilities (Details) - USD ($) $ in Thousands	Jul. 31, 2017	Jan. 31, 2017
Short-term investments:
Total short-term investments	$ 7,926	$ 0
Recurring
Cash equivalents:
Total cash equivalents	48,632	31,468
Total assets measured at fair value	56,558	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	7,926
Recurring | Corporate Debt Securities
Cash equivalents:
Total cash equivalents	11,954
Short-term investments:
Total short-term investments	5,931
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	36,678	31,468
Recurring | U.S. Government and Agency Securities
Short-term investments:
Total short-term investments	1,995
Recurring | Level 1
Cash equivalents:
Total cash equivalents	36,678	31,468
Total assets measured at fair value	36,678	31,468
Recurring | Level 1 | Money Market Funds
Cash equivalents:
Total cash equivalents	36,678	31,468
Recurring | Level 2
Cash equivalents:
Total cash equivalents	11,954
Total assets measured at fair value	19,880
Short-term investments:
Total short-term investments	7,926
Recurring | Level 2 | Corporate Debt Securities
Cash equivalents:
Total cash equivalents	11,954
Short-term investments:
Total short-term investments	5,931
Recurring | Level 2 | U.S. Government and Agency Securities
Short-term investments:
Total short-term investments	$ 1,995
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