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 Deficit
Beginning balance (in shares) at Dec. 31, 2018			77,456,180
Beginning balance at Dec. 31, 2018	$ 44,207		$ 77		$ 230,154		$ (186,024)
Increase (Decrease) in Stockholders' Equity [Roll Forward]
Net loss	(107,500)						(107,500)
Share-based compensation	$ 1,237				1,237
Exercise of stock awards and vesting of restricted stock awards (in shares)	90,000		89,812
Exercises of stock options and vesting of RSAs	$ 98				98
Sales of common stock under 2014 ESPP (in shares)			10,283
Sales of common stock under 2014 ESPP	8				8
Exercise of common stock warrants (in shares)			6,772,928
Exercise of common stock warrants	5,481		$ 7		5,474
Issuance of common stock and common stock warrants, net of issuance costs (in shares)			20,410,000	2,062,206
Issuance of common stock and common stock warrants, net of issuance costs	27,833	$ 1,936	$ 21	$ 2	27,812	$ 1,934
Ending balance (in shares) at Dec. 31, 2019			106,801,409
Ending balance at Dec. 31, 2019	(26,700)		$ 107		266,717		(293,524)
Increase (Decrease) in Stockholders' Equity [Roll Forward]
Net loss	(22,397)						(22,397)
Share-based compensation	$ 1,757				1,757
Exercise of stock awards and vesting of restricted stock awards (in shares)	12,000		12,000
Exercises of stock options and vesting of RSAs	$ 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
Exercise 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
Ending balance (in shares) at Dec. 31, 2020			140,449,647
Ending balance at Dec. 31, 2020	(9,227)		$ 140		306,554		(315,921)
Increase (Decrease) in Stockholders' Equity [Roll Forward]
Net loss	(336)						(336)
Share-based compensation	$ 5,143				5,143
Exercise of stock awards and vesting of restricted stock awards (in shares)	34,000		33,610
Exercises of stock options and vesting of RSAs	$ 42				42
Exercise of common stock warrants (in shares)	2,048,000		2,048,059
Exercise 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
Ending balance (in shares) at Dec. 31, 2021			199,463,645
Ending balance at Dec. 31, 2021	$ 171,710		$ 199		$ 487,768		$ (316,257)