CONDENSED CONSOLIDATED STATEMENTS OF REDEEMABLE CONVERTIBLE PREFERRED STOCK AND STOCKHOLDERS’ EQUITY (DEFICIT) - USD ($) $ in Thousands	Total	Class A and Class B Common Stock	Additional Paid-in Capital	Accumulated Other Comprehensive Income	Accumulated Deficit
Beginning balance (in shares) at Jan. 31, 2019	168,309,042
Beginning balance at Jan. 31, 2019	$ 910,853
Increase (Decrease) in Temporary Equity [Roll Forward]
Issuance of redeemable convertible preferred stock (in shares)	1,612,230
Issuance of redeemable convertible preferred stock	$ 24,121
Stock-based compensation	$ 1,500
Ending balance (in shares) at Oct. 31, 2019	169,921,272
Ending balance at Oct. 31, 2019	$ 936,474
Beginning balance (in shares) at Jan. 31, 2019		45,559,637
Beginning balance at Jan. 31, 2019	(312,467)	$ 5	$ 39,296	$ 16	$ (351,784)
Increase (Decrease) in Stockholders' Equity [Roll Forward]
Issuance of common stock upon exercise of stock options (in shares)		7,365,690
Issuance of common stock upon exercise of stock options	21,138		21,138
Repurchase of early exercised stock options and restricted common stock (in shares)		(520,557)
Repurchase of early exercised stock options and restricted common stock	0
Vesting of early exercised stock options and restricted common stock	5,474		5,474
Issuance of restricted common stock (in shares)		16,700
Issuance of restricted common stock	0
Issuance of common stock in connection with an acquisition (in shares)		661,635
Issuance of common stock in connection with an acquisition	4,749		4,749
Stock-based compensation	56,711		56,711
Other comprehensive income	238			238
Net loss	(265,281)				(265,281)
Ending balance (in shares) at Oct. 31, 2019		53,083,105
Ending balance at Oct. 31, 2019	$ (489,438)	$ 5	127,368	254	(617,065)
Beginning balance (in shares) at Jul. 31, 2019	169,159,160
Beginning balance at Jul. 31, 2019	$ 923,572
Increase (Decrease) in Temporary Equity [Roll Forward]
Issuance of redeemable convertible preferred stock (in shares)	762,112
Issuance of redeemable convertible preferred stock	$ 11,402
Stock-based compensation	$ 1,500
Ending balance (in shares) at Oct. 31, 2019	169,921,272
Ending balance at Oct. 31, 2019	$ 936,474
Beginning balance (in shares) at Jul. 31, 2019		48,094,553
Beginning balance at Jul. 31, 2019	(445,984)	$ 5	82,935	84	(529,008)
Increase (Decrease) in Stockholders' Equity [Roll Forward]
Issuance of common stock upon exercise of stock options (in shares)		5,033,760
Issuance of common stock upon exercise of stock options	18,203		18,203
Repurchase of early exercised stock options and restricted common stock (in shares)		(45,208)
Repurchase of early exercised stock options and restricted common stock	0
Vesting of early exercised stock options and restricted common stock	4,438		4,438
Stock-based compensation	21,792		21,792
Other comprehensive income	170			170
Net loss	(88,057)				(88,057)
Ending balance (in shares) at Oct. 31, 2019		53,083,105
Ending balance at Oct. 31, 2019	$ (489,438)	$ 5	127,368	254	(617,065)
Beginning balance (in shares) at Jan. 31, 2020	169,921,272
Beginning balance at Jan. 31, 2020	$ 936,474
Increase (Decrease) in Temporary Equity [Roll Forward]
Conversion of redeemable convertible preferred stock to common stock upon initial public offering (in shares)	(182,271,099)
Conversion of redeemable convertible preferred stock to common stock upon initial public offering	$ (1,415,047)
Issuance of redeemable convertible preferred stock (in shares)	12,349,827
Issuance of redeemable convertible preferred stock	$ 478,573
Ending balance (in shares) at Oct. 31, 2020	0
Ending balance at Oct. 31, 2020	$ 0
Beginning balance (in shares) at Jan. 31, 2020		55,452,421
Beginning balance at Jan. 31, 2020	(544,757)	$ 6	155,340	216	(700,319)
Increase (Decrease) in Stockholders' Equity [Roll Forward]
Conversion of redeemable convertible preferred stock to common stock upon initial public offering (in shares)		182,271,099
Conversion of redeemable convertible preferred stock to common stock upon initial public offering	1,415,047	$ 18	1,415,029
Issuance of common stock, new issues (in shares)		36,366,666
Issuance of common stock new issues	4,242,284	$ 4	4,242,280
Issuance of common stock upon exercise of stock options (in shares)		9,031,461
Issuance of common stock upon exercise of stock options	31,098		31,098
Exercise of common stock warrants (in shares)		32,241
Exercise of common stock warrants	0		0
Repurchase of early exercised stock options and restricted common stock (in shares)		(40,000)
Repurchase of early exercised stock options and restricted common stock	0
Vesting of early exercised stock options and restricted common stock	5,341		5,341
Vesting of restricted stock units (in shares)		5,657
Vesting of restricted stock units	0
Stock-based compensation	158,810		158,810
Other comprehensive income	159			159
Net loss	(340,167)				(340,167)
Ending balance (in shares) at Oct. 31, 2020		283,119,545
Ending balance at Oct. 31, 2020	$ 4,967,815	$ 28	6,007,898	375	(1,040,486)
Beginning balance (in shares) at Jul. 31, 2020	182,271,099
Beginning balance at Jul. 31, 2020	$ 1,415,047
Increase (Decrease) in Temporary Equity [Roll Forward]
Conversion of redeemable convertible preferred stock to common stock upon initial public offering (in shares)	(182,271,099)
Conversion of redeemable convertible preferred stock to common stock upon initial public offering	$ (1,415,047)
Ending balance (in shares) at Oct. 31, 2020	0
Ending balance at Oct. 31, 2020	$ 0
Beginning balance (in shares) at Jul. 31, 2020		62,257,063
Beginning balance at Jul. 31, 2020	(651,399)	$ 6	219,046	1,146	(871,597)
Increase (Decrease) in Stockholders' Equity [Roll Forward]
Conversion of redeemable convertible preferred stock to common stock upon initial public offering (in shares)		182,271,099
Conversion of redeemable convertible preferred stock to common stock upon initial public offering	1,415,047	$ 18	1,415,029
Issuance of common stock, new issues (in shares)		36,366,666
Issuance of common stock new issues	$ 4,242,284	$ 4	4,242,280
Issuance of common stock upon exercise of stock options (in shares)	2,186,819	2,186,819
Issuance of common stock upon exercise of stock options	$ 10,362		10,362
Exercise of common stock warrants (in shares)		32,241
Exercise of common stock warrants	0		0
Vesting of early exercised stock options and restricted common stock	1,756		1,756
Vesting of restricted stock units (in shares)		5,657
Vesting of restricted stock units	0
Stock-based compensation	119,425		119,425
Other comprehensive income	(771)			(771)
Net loss	(168,889)				(168,889)
Ending balance (in shares) at Oct. 31, 2020		283,119,545
Ending balance at Oct. 31, 2020	$ 4,967,815	$ 28	$ 6,007,898	$ 375	$ (1,040,486)