Consolidated Statements of Redeemable Convertible Preferred Stock and Stockholders' Equity (Deficit) - USD ($) $ in Thousands	Total	Initial Public Offering	Follow-On Offering	Common Stock	Common Stock Initial Public Offering	Common Stock Follow-On Offering	Additional Paid-In Capital	Additional Paid-In Capital Initial Public Offering	Additional Paid-In Capital Follow-On Offering	Accumulated Other Comprehensive Loss	Accumulated Deficit
Outstanding beginning of period (in shares) at Jan. 31, 2017	74,907,415
Outstanding value beginning of period at Jan. 31, 2017	$ 657,687
Increase (Decrease) in Temporary Equity [Roll Forward]
Conversion of redeemable convertible preferred stock to common stock in connection with initial public offering (in shares)	(74,907,415)
Conversion of redeemable convertible preferred stock to common stock in connection with initial public offering	$ (657,687)
Outstanding end of period (in shares) at Jan. 31, 2018	0
Outstanding value end of period at Jan. 31, 2018	$ 0
Outstanding beginning of period (in shares) at Jan. 31, 2017				38,156,688
Beginning balance at Jan. 31, 2017	(394,680)			$ 2			$ 192,795			$ (556)	$ (586,921)
Increase (Decrease) in Stockholders' Equity [Roll Forward]
Shares issued under employee stock plans (in shares)				5,281,193
Shares issued under employee stock plans	21,435						21,435
Vested restricted stock units converted into shares (in shares)				9,974,266
Conversion of redeemable convertible preferred stock to common stock in connection with initial public offering (in shares)				74,907,415
Conversion of redeemable convertible preferred stock to common stock in connection with initial public offering	657,687			$ 4			657,683
Issuance of common stock, net of offering costs (in shares)					17,250,000	3,000,000
Issuance of common stock, net of offering costs		$ 235,366	$ 46,008		$ 1			$ 235,365	$ 46,008
Stock-based compensation expense	290,006						290,006
Shares issued related to business combination (in shares)				358,206
Shares issued related to business combination	2,081						2,081
Shares withheld related to net settlement of restricted stock units (in shares)				(3,600,767)
Shares withheld related to net settlement of restricted stock units	(59,781)						(59,781)
Unrealized gain (loss) on investments	(625)									(625)
Foreign currency translation (loss) gain	349									349
Net loss	(369,672)										(369,672)
Outstanding end of period (in shares) at Jan. 31, 2018				145,327,001
Ending balance at Jan. 31, 2018	428,174			$ 7			1,385,592			(832)	(956,593)
Increase (Decrease) in Stockholders' Equity [Roll Forward]
Shares issued under employee stock plans (in shares)				3,827,218
Shares issued under employee stock plans	22,179						22,179
Vested restricted stock units converted into shares (in shares)				9,079,901
Stock-based compensation expense	117,365						117,365
Shares issued related to business combination (in shares)				111,304,700
Shares issued related to business combination	1,202,428			$ 6			1,202,422
Shares withheld related to net settlement of restricted stock units (in shares)				(720,193)
Shares withheld related to net settlement of restricted stock units	(16,218)						(16,218)
Unrealized gain (loss) on investments	756									756
Foreign currency translation (loss) gain	34									34
Net loss	(192,649)										(192,649)
Outstanding end of period (in shares) at Jan. 31, 2019				268,818,627
Ending balance at Jan. 31, 2019	1,562,069			$ 13			2,711,340			(42)	(1,149,242)
Increase (Decrease) in Stockholders' Equity [Roll Forward]
Shares issued under employee stock plans (in shares)				4,395,673
Shares issued under employee stock plans	12,676						12,676
Vested restricted stock units converted into shares (in shares)				23,273,233
Vested restricted stock units converted into shares	2			$ 2			0
Shares issued under employee stock plans (in shares)				2,497,928
Shares issued under employee stock plans	12,156						12,156
Stock-based compensation expense	220,354						220,354
Shares withheld related to net settlement of restricted stock units (in shares)				(3,817,700)
Shares withheld related to net settlement of restricted stock units	(32,621)						(32,621)
Unrealized gain (loss) on investments	1,250									1,250
Foreign currency translation (loss) gain	(935)									(935)
Net loss	(336,582)										(336,582)
Outstanding end of period (in shares) at Jan. 31, 2020				295,167,761
Ending balance at Jan. 31, 2020	$ 1,438,369			$ 15			$ 2,923,905			$ 273	$ (1,485,824)