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Income Taxes (Details) - USD ($)	12 Months Ended
Income Taxes (Details) - USD ($)	Jan. 31, 2021	Jan. 31, 2020	Jan. 31, 2019	Jan. 31, 2018
Operating Loss Carryforwards [Line Items]
Valuation allowance increase (decrease), amount	$ 206,200,000	$ 87,200,000	$ 36,000,000.0
Deferred tax assets, valuation allowance	413,828,000	207,596,000	120,400,000
Research and other credit carryforwards	22,778,000	15,355,000
Unrecognized tax benefits	24,447,000	5,469,000	$ 8,128,000	$ 8,128,000
Unrecognized tax benefits that would impact effective tax rate	600,000
Interest and penalties related to unrecognized tax benefits	0	$ 0
Domestic Tax Authority \| Federal
Operating Loss Carryforwards [Line Items]
Operating loss carryforwards	1,100,000,000
Research and other credit carryforwards	38,700,000
State and Local Jurisdiction \| California
Operating Loss Carryforwards [Line Items]
Operating loss carryforwards	122,600,000
Research and other credit carryforwards	8,700,000
State and Local Jurisdiction \| Other States
Operating Loss Carryforwards [Line Items]
Operating loss carryforwards	660,700,000
Foreign Tax Authority \| United Kingdom
Operating Loss Carryforwards [Line Items]
Operating loss carryforwards	$ 50,200,000