Condensed Consolidated Statements of Stockholders' Deficit (unaudited) - USD ($) $ in Thousands	Total	Common Stock	Additional Paid-in Capital	Accumulated Other Comprehensive Income (Loss)	Accumulated Deficit
Beginning balance (in shares) at Dec. 31, 2020		46,516,567,000
Beginning balance at Dec. 31, 2020	$ (102,260)	$ 46	$ 705,489	$ 4	$ (807,799)
Increase (Decrease) in Stockholders' Equity [Roll Forward]
Exercise of stock options (in shares)		961,000
Exercise of stock options	3		3
Issuance of common stock, net of expenses	0
Vesting of restricted stock unit awards (in shares)		389,700,000
Vesting of restricted stock unit awards	0	$ 1	(1)
Employee stock purchase plan expense	27		27
Unrealized gain (loss) on available-for-sale securities, net of tax	(4)			(4)
Stock-based compensation expense	1,572		1,572
Net loss	(18,346)				(18,346)
Ending balance (in shares) at Mar. 31, 2021		46,907,228,000
Ending balance at Mar. 31, 2021	(119,008)	$ 47	707,090	0	(826,145)
Beginning balance (in shares) at Dec. 31, 2021		51,711,809,000
Beginning balance at Dec. 31, 2021	$ (127,787)	$ 52	739,053	(9)	(866,883)
Increase (Decrease) in Stockholders' Equity [Roll Forward]
Exercise of stock options (in shares)	1,646	729,000
Exercise of stock options	$ 6		6
Issuance of common stock, net of expenses (in shares)		884,230,000
Issuance of common stock, net of expenses	3,091	$ 1	3,090
Vesting of restricted stock unit awards (in shares)		426,582,000
Vesting of restricted stock unit awards	0
Employee stock purchase plan expense	36		36
Unrealized gain (loss) on available-for-sale securities, net of tax	(171)			(171)
Stock-based compensation expense	2,433		2,433
Net loss	(17,910)				(17,910)
Ending balance (in shares) at Mar. 31, 2022		53,023,350,000
Ending balance at Mar. 31, 2022	$ (140,302)	$ 53	$ 744,618	$ (180)	$ (884,793)