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, 2016			24,531,964
Beginning balance at Dec. 31, 2016	$ 38,677		$ 25		$ 161,963		$ (123,311)
Increase (Decrease) in Stockholders' Equity [Roll Forward]
Net loss	(29,029)
Share-based compensation	$ 1,381				1,381
Exercise of stock awards and vesting of restricted stock awards (in shares)	140,000		161,453
Exercises of stock options and vesting of restricted stock awards	$ 40				40
Sales of common stock under 2014 ESPP (in shares)			9,148
Sales of common stock under 2014 ESPP	12				12
Issuance of common stock and common stock warrants, net of issuance costs (in shares)			5,525,000
Issuance of common stock and common stock warrants, net of issuance costs	6,908		$ 6		6,902
Exercise of common stock warrants (in shares)			4,475,000
Exercise of common stock warrants	45		$ 4		41
Ending balance (in shares) at Dec. 31, 2017			34,702,565
Ending 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]
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)	6,773,000		6,772,928
Exercise of common stock warrants	$ 5,481		$ 7		5,474
Ending balance (in shares) at Dec. 31, 2019			106,801,409
Ending balance at Dec. 31, 2019	$ (26,700)		$ 107		$ 266,717		$ (293,524)