CONSOLIDATED STATEMENTS OF CHANGES IN STOCKHOLDERS’ EQUITY (DEFICIT) - USD ($) $ in Thousands	Total	ATM Facility	Common Stock	Common Stock ATM Facility	Additional Paid-in Capital	Additional Paid-in Capital ATM Facility	Accumulated Other Comprehensive Loss Investments	Accumulated Deficit
Beginning balance (in shares) at Dec. 31, 2019			106,801,409
Beginning balance at Dec. 31, 2019	$ (26,700)		$ 107		$ 266,717		$ 0	$ (293,524)
Increase (Decrease) in Stockholders' Equity [Roll Forward]
Net loss	(22,397)							(22,397)
Share-based compensation	$ 1,757				1,757
Exercises of stock options (in shares)	12,000		12,000
Exercises of stock options	$ 13				13
Sales of common stock under 2014 ESPP (in shares)			28,186
Sales of common stock under 2014 ESPP	11				11
Exercise of common stock warrants (in shares)			238,110
Exercises of common stock warrants	131				131
Issuance of common stock and common stock warrants, net of issuance costs (in shares)				33,369,942
Issuance of common stock and common stock warrants, net of issuance costs	37,958			$ 33		$ 37,925
Unrealized loss on marketable securities	0
Ending balance (in shares) at Dec. 31, 2020			140,449,647
Ending balance at Dec. 31, 2020	(9,227)		$ 140		306,554		0	(315,921)
Increase (Decrease) in Stockholders' Equity [Roll Forward]
Net loss	(336)							(336)
Share-based compensation	$ 5,143				5,143
Exercises of stock options (in shares)	34,000		33,610
Exercises of stock options	$ 42				42
Exercise of common stock warrants (in shares)			2,048,059
Exercises of common stock warrants	1,126		$ 2		1,124
Issuance of common stock and common stock warrants, net of issuance costs (in shares)				56,932,329
Issuance of common stock and common stock warrants, net of issuance costs		$ 174,962		$ 57		$ 174,905
Unrealized loss on marketable securities	$ 0
Ending balance (in shares) at Dec. 31, 2021	199,463,645		199,463,645
Ending balance at Dec. 31, 2021	$ 171,710		$ 199		487,768		0	(316,257)
Increase (Decrease) in Stockholders' Equity [Roll Forward]
Net loss	(19,884)							(19,884)
Share-based compensation	$ 6,909				6,909
Exercises of stock options (in shares)	2,000		2,031
Exercises of stock options	$ 1				1
Exercise of common stock warrants (in shares)	0
Issuance of common stock for RSU vesting (in shares)			3,293,367
Issuance of common stock for RSU vesting	$ 0		$ 3		(3)
Unrealized loss on marketable securities	$ (546)						(546)
Ending balance (in shares) at Dec. 31, 2022	202,759,043		202,759,043
Ending balance at Dec. 31, 2022	$ 158,190		$ 202		$ 494,675		$ (546)	$ (336,141)