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		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 (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)	943,222	988,678
Exercise of stock options and vesting of restricted stock units	$ 1,736	$ 10	1,726
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	$ 99,914	$ 376	$ 390,981	$ (290,597)	$ (846)