Consolidated Statements of Stockholders' Equity - USD ($) $ in Thousands	Total	Public Offering	Public Offering, Excluding Related Parties	Public Offering, Related Parties	Private Placement	Common Shares	Common Shares Public Offering	Common Shares Public Offering, Excluding Related Parties	Common Shares Public Offering, Related Parties	Common Shares Private Placement	Additional Paid-in Capital	Additional Paid-in Capital Public Offering	Additional Paid-in Capital Public Offering, Excluding Related Parties	Additional Paid-in Capital Public Offering, Related Parties	Additional Paid-in Capital Private Placement	Accumulated Other Comprehensive Income	Accumulated Deficit
Beginning balance (in shares) at Dec. 31, 2018						12,648,000
Beginning balance at Dec. 31, 2018	$ (27,227)					$ 13					$ 567,768					$ 1	$ (595,009)
Increase (Decrease) in Stockholders' Equity [Roll Forward]
Issuance of common stock (in shares)								1,739,000	435,000	1,251,000
Issuance of common stock			$ 17,767	$ 5,000	$ 7,512			$ 2		$ 1			$ 17,765	$ 5,000	$ 7,511
Exercise of stock options (in shares)						8,000
Exercise of stock options	49										49
Stock-based compensation expense related to equity-classified awards	2,358										2,358
Unrealized loss on available-for-sale securities	(1)															(1)
Net income (loss)	9,388																9,388
Ending balance (in shares) at Dec. 31, 2019						16,081,000
Ending balance at Dec. 31, 2019	14,846					$ 16					600,451					0	(585,621)
Increase (Decrease) in Stockholders' Equity [Roll Forward]
Issuance of common stock (in shares)								5,221,000	4,504,000	1,070,000
Issuance of common stock			$ 24,079	$ 23,644	5,917			$ 5	$ 5	$ 1			$ 24,074	$ 23,639	5,916
Exercise of stock options (in shares)						1,000
Exercise of stock options	5										5
Stock-based compensation expense related to equity-classified awards	2,355										2,355
Issuance of common stock under employee stock purchase plan (in shares)						6,000
Issuance of common stock under employee stock purchase plan	32										32
Unrealized loss on available-for-sale securities	0
Net income (loss)	(35,584)																(35,584)
Ending balance (in shares) at Dec. 31, 2020						26,883,000
Ending balance at Dec. 31, 2020	35,294					$ 27					656,472					0	(621,205)
Increase (Decrease) in Stockholders' Equity [Roll Forward]
Issuance of common stock (in shares)							6,900,000			331,000
Issuance of common stock		$ 51,718			$ 3,377		$ 7					$ 51,711			$ 3,377
Issuance of common stock in connection with warrant exercises (in shares)						247,000
Issuance of common stock in connection with warrant exercises	$ 3,092										3,092
Exercise of stock options (in shares)	2,479					2,000
Exercise of stock options	$ 15										15
Stock-based compensation expense related to equity-classified awards	5,142										5,142
Issuance of common stock under employee stock purchase plan (in shares)						112,000
Issuance of common stock under employee stock purchase plan	577										577
Unrealized loss on available-for-sale securities	(3)															(3)
Net income (loss)	(53,342)																(53,342)
Ending balance (in shares) at Dec. 31, 2021						34,475,000
Ending balance at Dec. 31, 2021	$ 45,870					$ 34					$ 720,386					$ (3)	$ (674,547)