Income Taxes - Narrative (Details) - USD ($) $ in Thousands	12 Months Ended
	Jan. 31, 2021	Jan. 31, 2020	Jan. 31, 2019
Tax Credit Carryforward [Line Items]
Valuation allowance	$ 599,603	$ 165,067
Increase in valuation allowance	434,500	81,100	$ 47,200
Net operating loss carryforwards, U.S. federal	1,900,000
Net operating loss carryforwards, state	1,400,000
Net operating loss carryforwards, not subject to expiration	1,800,000
Net operating loss carryforward, subject to expiration	100,000
Interest and penalties	0	$ 0	$ 0
Federal
Tax Credit Carryforward [Line Items]
Tax credits	65,400
State
Tax Credit Carryforward [Line Items]
Tax credits	$ 31,300