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	12 Months Ended
	Jan. 31, 2020	Jan. 31, 2019	Jan. 31, 2018
Outstanding Stock Options
Beginning balance (in shares)	35,064,465
Granted (in shares)	1,576,150
Exercised (in shares)	(19,003,652)
Cancelled/forfeited/expired (in shares)	(803,954)
Ending balance (in shares)	16,833,009	35,064,465
Outstanding stock options, vested (in shares)	7,248,393
Weighted- Average Exercise Price
Beginning balance (in dollars per share)	$ 1.48
Granted (in dollars per share)	36.86
Exercised (in dollars per share)	0.49
Cancelled/forfeited/expired (in dollars per share)	5.15
Ending balance (in dollars per share)	5.73	$ 1.48
Weighted average exercise price, vested and exercisable (in shares)	$ 1.78
Share-based Compensation Arrangement by Share-based Payment Award, Options, Additional Disclosures [Abstract]
Weighted-average remaining contractual life (years)	7 years 7 months 6 days	6 years 9 months 18 days
Weighted-average remaining contractual life, vested and exercisable	6 years 9 months 18 days
Aggregate intrinsic value	$ 1,191,881	$ 534,572
Aggregate intrinsic value, exercised	767,336	$ 60,800	$ 2,500
Aggregate intrinsic value, vested and exercisable	$ 540,222