Short-term Investments - Summary of Short-term Investment (Details) - Short-term Investments - USD ($) $ in Thousands	Oct. 31, 2017	Jan. 31, 2017
Schedule Of Available For Sale Securities [Line Items]
Short-term Investments, Amortized Cost	$ 48,609	$ 49,222
Short-term Investments, Unrealized Losses	(36)	(22)
Short-term Investments, Unrealized Gains	1	11
Short-term Investments, Fair Value	48,574	49,211
Corporate Debt Securities
Schedule Of Available For Sale Securities [Line Items]
Short-term Investments, Amortized Cost	19,621	18,455
Short-term Investments, Unrealized Losses	(20)	(20)
Short-term Investments, Unrealized Gains	1	1
Short-term Investments, Fair Value	19,602	18,436
Commercial Paper
Schedule Of Available For Sale Securities [Line Items]
Short-term Investments, Amortized Cost	19,450	5,386
Short-term Investments, Unrealized Losses	(14)
Short-term Investments, Fair Value	19,436	5,386
U.S. Agency Securities
Schedule Of Available For Sale Securities [Line Items]
Short-term Investments, Amortized Cost	5,912	5,774
Short-term Investments, Unrealized Gains		3
Short-term Investments, Fair Value	5,912	5,777
U.S. Government Securities
Schedule Of Available For Sale Securities [Line Items]
Short-term Investments, Amortized Cost	2,746	17,793
Short-term Investments, Unrealized Losses	(2)	(2)
Short-term Investments, Unrealized Gains		7
Short-term Investments, Fair Value	2,744	17,798
Asset-backed Securities
Schedule Of Available For Sale Securities [Line Items]
Short-term Investments, Amortized Cost	880	1,814
Short-term Investments, Fair Value	$ 880	$ 1,814