Income Taxes - Additional Information (Details) - USD ($) $ in Thousands	12 Months Ended
	Jan. 31, 2020	Jan. 31, 2019	Jan. 31, 2018
Operating Loss Carryforwards [Line Items]
Employee stock purchase plan, compensation expense	$ 206,404	$ 410,978	$ 29,747
Tax benefit from compensation expense	1,000	1,700
Operating loss carryforwards limited to 80% of taxable income	105,800
Operating loss carryforwards not limited to 80% of taxable income	1,200,000
Unrecognized tax benefits that would affect tax rate, if recognized	2,500
Liability for uncertain tax positions	3,300	2,900	$ 2,500
Accrued interest and penalties	800
Increase (decrease) in valuation allowance	163,600	$ 163,000
Domestic Tax Authority
Operating Loss Carryforwards [Line Items]
Operating loss carryforwards	1,700,000
Research tax credit carryforwards	41,000
State and Local Jurisdiction
Operating Loss Carryforwards [Line Items]
Operating loss carryforwards	856,800
Research tax credit carryforwards	10,600
Foreign Tax Authority
Operating Loss Carryforwards [Line Items]
Operating loss carryforwards	$ 16,600