Consolidated Statements of Convertible Preferred Stock and Stockholders' Equity (Deficit) - USD ($) $ in Thousands	Total	Common Stock	Additional Paid-in Capital	Accumulated Other Comprehensive Loss	Accumulated Deficit	Treasury Stock	Convertible preferred stock
Temporary equity shares outstanding (in shares) at Jan. 31, 2017							43,594,000
Temporary equity, beginning of period at Jan. 31, 2017							$ 120,615
Increase (Decrease) in Temporary Equity [Roll Forward]
Conversion of preferred stock (in shares)							(43,594,000)
Conversion of preferred stock							$ (120,615)
Temporary equity shares outstanding (in shares) at Jan. 31, 2018							0
Temporary equity, end of period at Jan. 31, 2018							$ 0
Beginning of period (in shares) at Jan. 31, 2017		31,395,000
Beginning of period at Jan. 31, 2017	$ (127,755)	$ 38	$ 52,805	$ (1,808)	$ (166,885)	$ (11,905)
Increase (Decrease) in Stockholders' Equity [Roll Forward]
Common stock offering, net of issuance costs (in shares)		12,075,000
Initial public offering, net of issuance costs	119,094	$ 12	119,082
Conversion of preferred stock (in shares)		43,594,000
Conversion of preferred stock	120,615	$ 44	120,571
Conversion of preferred stock warrant	1,435		1,435
Exercise of stock options (in shares)		6,517,000
Exercise of stock options	11,610	$ 6	11,604
Exercise of common stock warrants (in shares)		179,000
Exercise of common stock warrants	79		79
Vested restricted stock units converted to common shares (in shares)		204,000
Vested restricted stock units converted to common shares	0
Issuance of restricted stock (in shares)		13,000
Issuance of restricted stock	0
Stock-based compensation	22,768		22,768
Other comprehensive income (loss)	172			172
Net loss	(66,565)				(66,565)
End of period (in shares) at Jan. 31, 2018		93,977,000
End of period at Jan. 31, 2018	81,453	$ 100	328,344	(1,636)	(233,450)	(11,905)
Increase (Decrease) in Stockholders' Equity [Roll Forward]
Issuance costs			4,433
Temporary equity shares outstanding (in shares) at Jan. 31, 2019							0
Temporary equity, end of period at Jan. 31, 2019							$ 0
Increase (Decrease) in Stockholders' Equity [Roll Forward]
Exercise of stock options (in shares)		5,901,000
Exercise of stock options	18,862	$ 5	18,857
Vested restricted stock units converted to common shares (in shares)		1,585,000
Vested restricted stock units converted to common shares	0	$ 3	(3)
Issuance of restricted stock (in shares)		16,000
Issuance of restricted stock	0
Stock-based compensation	44,907		44,907
Other comprehensive income (loss)	205			205
Net loss	(74,837)				(74,837)
Issuance of common stock under employee stock purchase plan (in shares)		694,000
Issuance of common stock under employee stock purchase plan	6,778	$ 1	6,777
End of period (in shares) at Jan. 31, 2019		102,173,000
End of period at Jan. 31, 2019	84,549	$ 109	398,882	(1,428)	(301,109)	(11,905)
Increase (Decrease) in Stockholders' Equity [Roll Forward]
Issuance costs			4,433
Temporary equity shares outstanding (in shares) at Jan. 31, 2020							0
Temporary equity, end of period at Jan. 31, 2020							$ 0
Increase (Decrease) in Stockholders' Equity [Roll Forward]
Common stock offering, net of issuance costs (in shares)		7,000,000
Initial public offering, net of issuance costs	$ 146,470	$ 7	146,463
Exercise of stock options (in shares)	3,307,708	3,308,000
Exercise of stock options	$ 14,855	$ 3	14,852
Vested restricted stock units converted to common shares (in shares)		2,946,000
Vested restricted stock units converted to common shares	0	$ 3	(3)
Issuance of restricted stock (in shares)		11,000
Issuance of restricted stock	0
Stock-based compensation	69,187		69,187
Other comprehensive income (loss)	1,068			1,068
Net loss	(121,544)				(121,544)
Issuance of common stock under employee stock purchase plan (in shares)		392,000
Issuance of common stock under employee stock purchase plan	6,627		6,627
End of period (in shares) at Jan. 31, 2020		115,830,000
End of period at Jan. 31, 2020	$ 201,212	$ 122	636,008	$ (360)	$ (422,653)	$ (11,905)
Increase (Decrease) in Stockholders' Equity [Roll Forward]
Issuance costs			$ 530