Fair Value Measurements (Details) - USD ($) $ in Thousands	Apr. 30, 2020	Jan. 31, 2020
Assets Measured on Recurring Basis
Short-term investments	$ 87,898	$ 117,662
U.S. government securities
Assets Measured on Recurring Basis
Short-term investments	22,177	34,094
Corporate bonds
Assets Measured on Recurring Basis
Short-term investments	41,691	45,682
Commercial paper
Assets Measured on Recurring Basis
Short-term investments	24,030	37,886
Recurring
Assets Measured on Recurring Basis
Short-term investments	87,898	117,662
Recurring | Money market funds
Assets Measured on Recurring Basis
Cash equivalents	64,868	37,906
Recurring | U.S. government securities
Assets Measured on Recurring Basis
Short-term investments	22,177	34,094
Recurring | Corporate bonds
Assets Measured on Recurring Basis
Short-term investments	41,691	45,682
Recurring | Commercial paper
Assets Measured on Recurring Basis
Short-term investments	24,030	37,886
Recurring | Level 1
Assets Measured on Recurring Basis
Short-term investments	0	0
Recurring | Level 1 | Money market funds
Assets Measured on Recurring Basis
Cash equivalents	64,868	37,906
Recurring | Level 1 | U.S. government securities
Assets Measured on Recurring Basis
Short-term investments	0	0
Recurring | Level 1 | Corporate bonds
Assets Measured on Recurring Basis
Short-term investments	0	0
Recurring | Level 1 | Commercial paper
Assets Measured on Recurring Basis
Short-term investments	0	0
Recurring | Level 2
Assets Measured on Recurring Basis
Short-term investments	87,898	117,662
Recurring | Level 2 | Money market funds
Assets Measured on Recurring Basis
Cash equivalents	0	0
Recurring | Level 2 | U.S. government securities
Assets Measured on Recurring Basis
Short-term investments	22,177	34,094
Recurring | Level 2 | Corporate bonds
Assets Measured on Recurring Basis
Short-term investments	41,691	45,682
Recurring | Level 2 | Commercial paper
Assets Measured on Recurring Basis
Short-term investments	24,030	37,886
Recurring | Level 3
Assets Measured on Recurring Basis
Short-term investments	0	0
Recurring | Level 3 | Money market funds
Assets Measured on Recurring Basis
Cash equivalents	0	0
Recurring | Level 3 | U.S. government securities
Assets Measured on Recurring Basis
Short-term investments	0	0
Recurring | Level 3 | Corporate bonds
Assets Measured on Recurring Basis
Short-term investments	0	0
Recurring | Level 3 | Commercial paper
Assets Measured on Recurring Basis
Short-term investments	$ 0	$ 0