Convertible Preferred Stock, Stockholders’ Equity (Deficit) and Equity Incentive Plan - Summary of Stock Option Activity Under Equity Incentive Plan (Details) - USD ($) $ / shares in Units, $ in Thousands	3 Months Ended		6 Months Ended
	Jul. 31, 2019	Apr. 30, 2019	Jul. 31, 2019
Outstanding Stock Options
Beginning balance (in shares)	35,064,465
Granted (in shares)			1,537,900
Exercised (in shares)			(14,272,059)
Cancelled/forfeited/expired (in shares)			(284,118)
Ending balance (in shares)	22,046,188	35,064,465	22,046,188
Weighted- Average Exercise Price
Beginning balance (in dollars per share)	$ 1.48
Granted (in dollars per share)			$ 36.77
Exercised (in dollars per share)			0.16
Cancelled/forfeited/expired (in dollars per share)			6.11
Ending balance (in dollars per share)	$ 4.73	$ 1.48	$ 4.73
Weighted- Average Remaining Contractual Life (Years)		6 years 9 months 18 days	8 years
Options Outstanding, Aggregate Intrinsic Value	$ 2,001,410	$ 534,572	$ 2,001,410
Outstanding Stock Options, Vested (in shares)	8,692,345		8,692,345
Weighted Average Exercise price, Vested (in shares)	$ 1.02		$ 1.02
Weighted-Average Remaining Contractual Life (Years), Vested			7 years 1 month 6 days
Options Outstanding, Aggregate Intrinsic Value, Vested	$ 821,380		$ 821,380