CONSOLIDATED STATEMENTS OF CHANGES IN STOCKHOLDERS’ (DEFICIT) EQUITY - 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, 2017			34,702,565
Beginning balance at Dec. 31, 2017	$ 18,034		$ 35		$ 170,330		$ (152,331)
Increase (Decrease) in Stockholders' Equity [Roll Forward]
Net loss	(33,693)
Share-based compensation	$ 1,283				1,283
Exercise of stock awards and vesting of restricted stock awards (in shares)	439,000		443,443
Exercises of stock options and vesting of restricted stock awards	$ 277				277
Sales of common stock under 2014 ESPP (in shares)			20,992
Sales of common stock under 2014 ESPP	20				20
Issuance of common stock and common stock warrants, net of issuance costs (in shares)			33,523,684
Issuance of common stock and common stock warrants, net of issuance costs	50,971		$ 33		50,938
Exercise of common stock warrants (in shares)			8,765,496
Exercise of common stock warrants	7,315		$ 9		7,306
Ending balance (in shares) at Dec. 31, 2018			77,456,180
Ending balance at Dec. 31, 2018	44,207		$ 77		230,154		(186,024)
Increase (Decrease) in Stockholders' Equity [Roll Forward]
Issuance costs	5,029
Net loss	(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 restricted stock awards	$ 98				98
Sales of common stock under 2014 ESPP (in shares)			10,283
Sales of common stock under 2014 ESPP	8				8
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
Exercise of common stock warrants (in shares)			6,772,928
Exercise of common stock warrants	$ 5,481		$ 7		5,474
Ending balance (in shares) at Dec. 31, 2019	106,800,000		106,801,409
Ending balance at Dec. 31, 2019	$ (26,700)		$ 107		266,717		(293,524)
Increase (Decrease) in Stockholders' Equity [Roll Forward]
Issuance costs	2,171	212
Net loss	(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 restricted stock awards	$ 13				13
Sales of common stock under 2014 ESPP (in shares)			28,186
Sales of common stock under 2014 ESPP	$ 11				11
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
Exercise of common stock warrants (in shares)	238,000		238,110
Exercise of common stock warrants	$ 131		$ 0		131
Ending balance (in shares) at Dec. 31, 2020	140,400,000		140,449,647
Ending balance at Dec. 31, 2020	$ (9,227)		$ 140		$ 306,554		$ (315,921)
Increase (Decrease) in Stockholders' Equity [Roll Forward]
Issuance costs		$ 1,174