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Income Taxes (Details) - USD ($)	12 Months Ended
Income Taxes (Details) - USD ($)	Jan. 31, 2020	Jan. 31, 2019	Jan. 31, 2018	Jan. 31, 2017
Operating Loss Carryforwards [Line Items]
Valuation allowance increase (decrease), amount	$ 87,200,000	$ 36,000,000.0	$ 12,200,000
Deferred tax assets, valuation allowance	207,596,000	120,391,000	84,400,000	$ 72,200,000
Research credit carryforwards	15,355,000	11,102,000
Unrecognized tax benefits	5,469,000	8,128,000	$ 8,128,000	$ 5,060,000
Unrecognized tax benefits that would impact effective tax rate	0
Interest and penalties related to unrecognized tax benefits	0	$ 0
Domestic Tax Authority \| Federal
Operating Loss Carryforwards [Line Items]
Operating loss carryforwards	657,300,000
Research credit carryforwards	17,200,000
State and Local Jurisdiction \| California
Operating Loss Carryforwards [Line Items]
Operating loss carryforwards	94,800,000
Research credit carryforwards	4,300,000
State and Local Jurisdiction \| Other States
Operating Loss Carryforwards [Line Items]
Operating loss carryforwards	352,800,000
Foreign Tax Authority \| United Kingdom
Operating Loss Carryforwards [Line Items]
Operating loss carryforwards	$ 15,300,000