Unaudited statements of redeemable preferred stock and stockholders' equity (deficit) - USD ($) $ in Thousands	Total	Common Stock	APIC	Accumulated Deficit	Treasury stock	Series A	Series B	Junior Preferred	Redeemable Preferred
Beginning balance, redeemable preferred stock (in shares) at Jan. 31, 2019						13,674,365	9,197,142	32,746,041	42,560,530
Beginning balance, redeemable preferred stock at Jan. 31, 2019	$ 206,490					$ 79,311	$ 51,872	$ 32,746	$ 42,561
Redeemable Preferred Stock
Accretion of redeemable preferred stock	7,863					$ 5,196	$ 2,667
Ending balance, redeemable preferred stock (in shares) at Apr. 30, 2019						13,674,365	9,197,142	32,746,041	42,560,530
Ending balance, redeemable preferred stock at Apr. 30, 2019	214,353					$ 84,507	$ 54,539	$ 32,746	$ 42,561
Beginning balance (in shares) at Jan. 31, 2019		1,994,721
Beginning balance at Jan. 31, 2019	(210,974)	$ 20	$ 0	$ (210,994)	$ 0
Stockholders' Equity (Deficit)
Net loss	(6,695)			(6,695)
Stock-based compensation expense	599		599
Exercise of stock options and vesting of restricted stock (in shares)		29,798
Exercise of stock options and vesting of restricted stock units	37	$ 0	37
Issuance of common stock warrants	833		833
Accretion of redeemable preferred stock	(7,863)		(1,469)	(6,394)
Ending balance (in shares) at Apr. 30, 2019		2,024,519
Ending balance at Apr. 30, 2019	(224,063)	$ 20	0	(224,083)	0
Beginning balance, redeemable preferred stock (in shares) at Jan. 31, 2019						13,674,365	9,197,142	32,746,041	42,560,530
Beginning balance, redeemable preferred stock at Jan. 31, 2019	206,490					$ 79,311	$ 51,872	$ 32,746	$ 42,561
Ending balance, redeemable preferred stock (in shares) at Oct. 31, 2019						0	0	0	0
Ending balance, redeemable preferred stock at Oct. 31, 2019	0					$ 0	$ 0	$ 0	$ 0
Beginning balance (in shares) at Jan. 31, 2019		1,994,721
Beginning balance at Jan. 31, 2019	(210,974)	$ 20	0	(210,994)	0
Stockholders' Equity (Deficit)
Net loss	(16,625)
Ending balance (in shares) at Oct. 31, 2019		35,872,057
Ending balance at Oct. 31, 2019	102,494	$ 359	382,951	(280,817)	0
Beginning balance, redeemable preferred stock (in shares) at Apr. 30, 2019						13,674,365	9,197,142	32,746,041	42,560,530
Beginning balance, redeemable preferred stock at Apr. 30, 2019	214,353					$ 84,507	$ 54,539	$ 32,746	$ 42,561
Redeemable Preferred Stock
Accretion of redeemable preferred stock	48,312					$ 27,510	$ 20,802
Conversion of preferred stock into common stock and cancellation of redeemable preferred stock (in shares)						(13,674,365)	(9,197,142)	(32,746,041)	(42,560,530)
Conversion of preferred stock into common stock and cancellation of redeemable preferred stock	(262,665)					$ (112,017)	$ (75,341)	$ (32,746)	$ (42,561)
Ending balance, redeemable preferred stock (in shares) at Jul. 31, 2019						0	0	0	0
Ending balance, redeemable preferred stock at Jul. 31, 2019	0					$ 0	$ 0	$ 0	$ 0
Beginning balance (in shares) at Apr. 30, 2019		2,024,519
Beginning balance at Apr. 30, 2019	(224,063)	$ 20	0	(224,083)	0
Stockholders' Equity (Deficit)
Net loss	(7,493)			(7,493)
Stock-based compensation expense	1,467		1,467
Exercise of stock options and vesting of restricted stock (in shares)		22,038
Exercise of stock options and vesting of restricted stock units	41	$ 0	41
Accretion of redeemable preferred stock	(48,312)		(1,508)	(46,804)
Payment of preferred stock dividends	(14,955)		(14,955)
Issuance of common stock in public offering, net of issuance costs (in shares)		7,812,500
Issuance of common stock in public offering, net of issuance costs	124,698	$ 78	124,619
Conversion of preferred stock into common stock and cancellation of redeemable preferred stock (in shares)		25,311,535
Conversion of preferred stock into common stock and cancellation of redeemable preferred stock	262,665	$ 253	262,412
Conversion and exercise of preferred stock warrants into common stock (shares)		588,763
Conversion and exercise of preferred stock warrants into common stock	8,805	$ 6	8,799
Deferred offering costs	(6,084)
Ending balance (in shares) at Jul. 31, 2019		35,759,355
Ending balance at Jul. 31, 2019	102,853	$ 357	380,875	(278,380)	0
Ending balance, redeemable preferred stock (in shares) at Oct. 31, 2019						0	0	0	0
Ending balance, redeemable preferred stock at Oct. 31, 2019	0					$ 0	$ 0	$ 0	$ 0
Stockholders' Equity (Deficit)
Net loss	(2,437)			(2,437)
Stock-based compensation expense	1,766		1,766
Exercise of stock options and vesting of restricted stock (in shares)		59,679
Exercise of stock options and vesting of restricted stock units	366	$ 1	365
Cashless exercise of common stock warrants (in shares)		53,023
Cashless exercise of common stock warrants	2	$ 1	1
Deferred offering costs	(56)		(56)
Ending balance (in shares) at Oct. 31, 2019		35,872,057
Ending balance at Oct. 31, 2019	102,494	$ 359	382,951	(280,817)	0
Beginning balance (in shares) at Jan. 31, 2020		36,610,763
Beginning balance at Jan. 31, 2020	101,865	$ 366	386,383	(284,485)	(399)
Stockholders' Equity (Deficit)
Net loss	(6,112)			(6,112)
Stock-based compensation expense	2,872		2,872
Exercise of stock options and vesting of restricted stock (in shares)		988,678
Exercise of stock options and vesting of restricted stock units	1,737	$ 10	1,727
Treasury stock from vesting of restricted stock units	(447)				(447)
Ending balance (in shares) at Apr. 30, 2020		37,599,441
Ending balance at Apr. 30, 2020	99,915	$ 376	390,982	(290,597)	(846)
Beginning balance (in shares) at Jan. 31, 2020		36,610,763
Beginning balance at Jan. 31, 2020	101,865	$ 366	386,383	(284,485)	(399)
Stockholders' Equity (Deficit)
Net loss	$ (19,196)
Exercise of stock options and vesting of restricted stock (in shares)	1,610,207
Ending balance (in shares) at Oct. 31, 2020		44,039,563
Ending balance at Oct. 31, 2020	$ 269,676	$ 440	573,786	(303,681)	(869)
Beginning balance (in shares) at Apr. 30, 2020		37,599,441
Beginning balance at Apr. 30, 2020	99,915	$ 376	390,982	(290,597)	(846)
Stockholders' Equity (Deficit)
Net loss	(6,371)			(6,371)
Stock-based compensation expense	3,428		3,428
Exercise of stock options and vesting of restricted stock (in shares)		283,396
Exercise of stock options and vesting of restricted stock units	738	$ 3	735
Treasury stock from vesting of restricted stock units	(23)				(23)
Ending balance (in shares) at Jul. 31, 2020		37,882,837
Ending balance at Jul. 31, 2020	97,687	$ 379	395,145	(296,968)	(869)
Stockholders' Equity (Deficit)
Net loss	(6,713)			(6,713)
Stock-based compensation expense	3,316		3,316
Exercise of stock options and vesting of restricted stock (in shares)		406,726
Exercise of stock options and vesting of restricted stock units	876	$ 4	872
Issuance of common stock in public offering, net of issuance costs (in shares)		5,750,000
Issuance of common stock in public offering, net of issuance costs	174,510	$ 57	174,453
Deferred offering costs	(290)
Ending balance (in shares) at Oct. 31, 2020		44,039,563
Ending balance at Oct. 31, 2020	$ 269,676	$ 440	$ 573,786	$ (303,681)	$ (869)