Condensed Consolidated Statements of Stockholders' Equity - USD ($) $ in Thousands	Total	Preferred Stock Convertible Preferred Stock	Common Stock	Common Stock Common Class A	Common Stock Common Class B	Additional Paid-In Capital	Accumulated Other Comprehensive Loss	Accumulated Deficit
Beginning balance at Jan. 31, 2019	$ (6,558)	$ 72	$ 0	$ 30	$ 0	$ 363,076	$ (1,096)	$ (368,640)
Beginning balance (in shares) at Jan. 31, 2019		72,482,609	0	29,755,883	3,000
Increase (Decrease) in Stockholders' Equity [Roll Forward]
Exercise of employee stock options	13,010		$ 2	$ 1		13,007
Exercise of employee stock options (in shares)			1,889,293	1,370,818
Conversion of common stock			$ 31	$ (31)
Conversion of common stock (in shares)			31,129,701	(31,126,701)	(3,000)
Conversion of preferred stock		$ (77)	$ 77
Conversion of preferred stock (in shares)		(77,149,275)	77,149,275
Proceeds from initial public offering, net of issuance and underwriters' discounts and commissions and concurrent private placement	319,572		$ 17			319,555
Proceeds from initial public offering, net of issuance and underwriters' discounts and commissions and concurrent private placement (in shares)			16,680,000
Repurchase of early exercised stock options (in shares)			(625)
Issuance of Series F preferred shares, net of issuance costs	69,848	$ 5				69,843
Issuance of Series F preferred shares, net of issuance costs (in shares)		4,666,666
Vesting of early exercised stock options	392					392
Warrant exercises (in shares)			73,299
Stock-based compensation	43,141					43,141
Other comprehensive loss	(1,031)						(1,031)
Net loss	(40,843)							(40,843)
Ending balance at Jul. 31, 2019	397,531	$ 0	$ 127	$ 0	$ 0	809,014	(2,127)	(409,483)
Ending balance (in shares) at Jul. 31, 2019		0	126,920,943	0	0
Beginning balance at Apr. 30, 2019	73,767	$ 77	$ 0	$ 31	$ 0	446,355	(1,497)	(371,199)
Beginning balance (in shares) at Apr. 30, 2019		77,149,275	0	31,126,701	3,000
Increase (Decrease) in Stockholders' Equity [Roll Forward]
Exercise of employee stock options	7,742		$ 2			7,740
Exercise of employee stock options (in shares)			1,889,293
Conversion of common stock			$ 31	$ (31)
Conversion of common stock (in shares)			31,129,701	(31,126,701)	(3,000)
Conversion of preferred stock	$ (77)		$ 77
Conversion of preferred stock (in shares)	(77,149,275)		77,149,275
Proceeds from initial public offering, net of issuance and underwriters' discounts and commissions and concurrent private placement	$ 319,572		$ 17			319,555
Proceeds from initial public offering, net of issuance and underwriters' discounts and commissions and concurrent private placement (in shares)			16,680,000
Repurchase of early exercised stock options (in shares)			(625)
Vesting of early exercised stock options	185					185
Warrant exercises (in shares)			73,299
Stock-based compensation	35,179					35,179
Other comprehensive loss	(630)						(630)
Net loss	(38,284)							(38,284)
Ending balance at Jul. 31, 2019	397,531	$ 0	$ 127	$ 0	$ 0	809,014	(2,127)	(409,483)
Ending balance (in shares) at Jul. 31, 2019		0	126,920,943	0	0
Beginning balance at Jan. 31, 2020	397,796	$ 0	$ 132	$ 0	$ 0	878,843	(206)	(480,973)
Beginning balance (in shares) at Jan. 31, 2020		0	132,346,402	0	0
Increase (Decrease) in Stockholders' Equity [Roll Forward]
Exercise of employee stock options	$ 40,694		$ 9			40,685
Exercise of employee stock options (in shares)	9,853,483		9,853,483
Release of restricted stock units (in shares)			2,762,734
Issuance of shares from share purchase plan	$ 10,267		$ 1			10,266
Issuance of shares from share purchase plan (in shares)			591,732
Stock-based compensation	56,438					56,438
Other comprehensive loss	(1,365)						(1,365)
Net loss	(67,727)							(67,727)
Ending balance at Jul. 31, 2020	436,103	$ 0	$ 142	$ 0	$ 0	986,232	(1,571)	(548,700)
Ending balance (in shares) at Jul. 31, 2020		0	145,554,351	0	0
Beginning balance at Apr. 30, 2020	423,521	$ 0	$ 139	$ 0	$ 0	939,841	(2,957)	(513,502)
Beginning balance (in shares) at Apr. 30, 2020		0	139,794,418	0	0
Increase (Decrease) in Stockholders' Equity [Roll Forward]
Exercise of employee stock options	21,760		$ 3			21,757
Exercise of employee stock options (in shares)			4,668,851
Release of restricted stock units (in shares)			1,091,082
Stock-based compensation	24,634					24,634
Other comprehensive loss	1,386						1,386
Net loss	(35,198)							(35,198)
Ending balance at Jul. 31, 2020	$ 436,103	$ 0	$ 142	$ 0	$ 0	$ 986,232	$ (1,571)	$ (548,700)
Ending balance (in shares) at Jul. 31, 2020		0	145,554,351	0	0