Consolidated Statement of Redeemable Convertible Preferred Stock and Stockholders' Equity (Deficit) - USD ($) shares in Thousands, $ in Thousands	Total	Common Stock	Additional Paid-In Capital	Accumulated Other Comprehensive Loss (Income)	Accumulated Deficit	Redeemable Convertible Preferred Stock
Beginning balance (in shares) at Jan. 31, 2017		29,439
Beginning balance at Jan. 31, 2017	$ (347,355)	$ 3	$ 105,432	$ (2,746)	$ (450,044)
Increase (Decrease) in Stockholders' Equity [Roll Forward]
Exercise of stock options (in shares)		6,261
Exercise of stock options	26,433	$ 1	26,432
Employee stock-based compensation expense	28,496		28,496
Non-employee stock-based compensation expense	1,366		1,366
Accretion of preferred stock	(1,461)		(1,461)
Net loss	(52,276)				(52,276)
Other comprehensive income, net	6,149			6,149
Ending balance (in shares) at Jan. 31, 2018		35,700
Ending balance at Jan. 31, 2018	(338,648)	$ 4	160,265	3,403	(502,320)
Beginning balance (in shares) at Jan. 31, 2017						100,226
Beginning balance at Jan. 31, 2017						$ 546,040
Increase (Decrease) in Temporary Equity [Roll Forward]
Accretion of preferred stock	(1,461)					$ 1,461
Ending balance (in shares) at Jan. 31, 2018						100,226
Ending balance at Jan. 31, 2018						$ 547,501
Increase (Decrease) in Stockholders' Equity [Roll Forward]
Exercise of stock options (in shares)		5,791
Exercise of stock options	50,211		50,211
Settlement of RSUs (in shares)		8,126
Settlement of RSUs	0	$ 1	(1)
Tax withholding on RSU settlement	(215,332)		(215,332)
Employee stock-based compensation expense	411,803		411,803
Non-employee stock-based compensation expense	1,058		1,058
Accretion of preferred stock	(353)		(353)
Issuance of common stock in connection with initial public offering, net of offering costs (in shares)		19,314
Issuance of common stock in connection with initial public offering, net of offering costs	524,979	$ 2	524,977
Conversion of redeemable convertible preferred stock to common stock in connection with initial public offering (in shares)		100,350
Conversion of redeemable convertible preferred stock to common stock in connection with initial public offering	547,854	$ 10	547,844
Conversion of preferred stock warrant to common stock warrant in connection with initial public offering	848		848
Equity component of convertible senior notes	131,331		131,331
Purchase of capped calls related to issuance of convertible senior notes	(67,563)		(67,563)
Exercise of common stock warrants (in shares)		22
Net loss	(426,458)				(426,458)
Other comprehensive income, net	(5,368)			(5,368)
Ending balance (in shares) at Jan. 31, 2019		169,303
Ending balance at Jan. 31, 2019	614,362	$ 17	1,545,088	(1,965)	(928,778)
Increase (Decrease) in Temporary Equity [Roll Forward]
Accretion of preferred stock	$ (353)					$ 353
Conversion of redeemable convertible preferred stock to common stock in connection with initial public offering (in shares)						(100,226)
Conversion of redeemable convertible preferred stock to common stock in connection with initial public offering						$ (547,854)
Ending balance (in shares) at Jan. 31, 2019						0
Ending balance at Jan. 31, 2019						$ 0
Increase (Decrease) in Stockholders' Equity [Roll Forward]
Exercise of stock options (in shares)	6,737	6,737
Exercise of stock options	$ 72,177	$ 1	72,176
Settlement of RSUs (in shares)		4,706
Settlement of RSUs	0
Tax withholding on RSU settlement	(166,504)		(166,504)
Employee stock purchase plan (in shares)		508
Employee stock purchase plan	23,872		23,872
Employee stock-based compensation expense	210,535		210,535
Conversion of preferred stock warrant to common stock warrant in connection with initial public offering	800
Net loss	(208,359)				(208,359)
Other comprehensive income, net	292			292
Ending balance (in shares) at Jan. 31, 2020		181,254
Ending balance at Jan. 31, 2020	546,327	$ 18	$ 1,685,167	$ (1,673)	$ (1,137,185)
Increase (Decrease) in Temporary Equity [Roll Forward]
Accretion of preferred stock	$ 0