Employee Incentive Plans - Narrative (Details) $ / shares in Units, $ in Millions	9 Months Ended
	Oct. 31, 2020 USD ($) incentive_plan purchase_period $ / shares shares	Jan. 31, 2020 shares
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]
Number of equity incentive plans (in incentive plans) | incentive_plan	2
Options to purchase common stock outstanding (in shares) | shares	9,242,208	12,359,302
Unrecognized stock-based compensation expense related to stock options | $	$ 36.2
Unrecognized stock-based compensation expenses related to unvested RSUs | $	$ 501.8
Stock options
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]
Weighted average stock-based compensation recognition period	1 year 6 months
Restricted stock units
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]
Weighted average stock-based compensation recognition period	2 years 7 months 6 days
ESPP
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]
Weighted average stock-based compensation recognition period	6 months
Offering period	12 months
Number of stock plan purchase periods | purchase_period	2
Stock plan purchase period	6 months
Shares of employee purchased Class A common stock (in shares) | shares	127,734
Weighted-average purchase price of employee purchased Class A common stock (in dollars per share) | $ / shares	$ 100.38
Total proceeds from employee purchase of Class A common stock | $	$ 12.8
Unrecognized compensation costs related to unvested restricted stock units | $	$ 2.0
2017 Equity Incentive Plan | Class A Common Stock
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]
Options to purchase common stock outstanding (in shares) | shares	1,176,642
2017 Equity Incentive Plan | Class B Common Stock
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]
Options to purchase common stock outstanding (in shares) | shares	8,065,566