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	12 Months Ended
	Apr. 30, 2019	Jan. 31, 2019
Stockholders Equity Note [Abstract]
Outstanding Stock Options, Beginning balance	35,064,465
Outstanding Stock Options, Granted	1,324,650
Outstanding Stock Options Exercised	(13,622,754)
Outstanding Stock Options Cancelled/forfeited/expired	(142,301)
Outstanding Stock Options, Ending balance	22,624,060	35,064,465
Outstanding Stock Options, Vested	7,516,678
Weighted Average Exercise Price, Beginning balance	$ 1.48
Weighted Average Exercise Price, Granted	27.42
Weighted Average Exercise Price Exercised	0.14
Weighted Average Exercise Price Cancelled/forfeited/expired	4.60
Weighted Average Exercise price, Ending balance	3.78	$ 1.48
Weighted Average Exercise price, Vested	$ 0.76
Weighted-Average Remaining Contractual Life (Years)	8 years 2 months 12 days	6 years 9 months 18 days
Weighted-Average Remaining Contractual Life (Years), Vested	7 years 1 month 6 days
Options Outstanding, Aggregate Intrinsic Value, Beginning balance	$ 534,572
Options Outstanding, Aggregate Intrinsic Value, Ending balance	1,554,000	$ 534,572
Options Outstanding, Aggregate Intrinsic Value, Vested	$ 539,010