CONDENSED CONSOLIDATED STATEMENTS OF CHANGES IN STOCKHOLDERS' EQUITY (Unaudited) - USD ($) $ in Thousands	Total	Common Stock	Additional Paid-in Capital	Accumulated Deficit
Increase (Decrease) in Stockholders' Equity [Roll Forward]
Beginning balance (in shares)		34,702,565
Beginning balance (in shares)		43,105,466
Beginning balance at Dec. 31, 2017	$ 18,034	$ 35	$ 170,330	$ (152,331)
Increase (Decrease) in Stockholders' Equity [Roll Forward]
Net loss	(3,963)			(3,963)
Share-based compensation	401		401
Sales of common stock under 2014 ESPP (in shares)		9,565
Sales of common stock under 2014 ESPP	10		10
Exercise of stock options and vesting of restricted stock awards (in shares)		4,430
Exercises of stock options and vestings of restricted stock awards	0
Exercises of common stock warrants (in shares)		420,778
Exercises of common stock warrants	336		336
Issuance of common stock and common stock warrants, net of issuance costs (in shares)		7,968,128
Issuance of common stock and common stock warrants, net of issuance costs	9,040	$ 8	9,032
Ending balance (in shares) at Mar. 31, 2018		43,105,466
Ending balance at Mar. 31, 2018	23,858	$ 43	180,109	(156,294)
Increase (Decrease) in Stockholders' Equity [Roll Forward]
Beginning balance (in shares)		77,088,570
Beginning balance at Dec. 31, 2017	18,034	$ 35	170,330	(152,331)
Increase (Decrease) in Stockholders' Equity [Roll Forward]
Net loss	(26,936)
Exercises of common stock warrants (in shares)		8,700,000
Ending balance (in shares) at Sep. 30, 2018		77,088,570
Ending balance at Sep. 30, 2018	50,395	$ 77	229,585	(179,267)
Increase (Decrease) in Stockholders' Equity [Roll Forward]
Beginning balance (in shares)		43,105,466
Beginning balance (in shares)		77,010,999
Beginning balance at Mar. 31, 2018	23,858	$ 43	180,109	(156,294)
Increase (Decrease) in Stockholders' Equity [Roll Forward]
Net loss	(8,958)			(8,958)
Share-based compensation	285		285
Exercise of stock options and vesting of restricted stock awards (in shares)		55,259
Exercises of stock options and vestings of restricted stock awards	29		29
Exercises of common stock warrants (in shares)		8,294,718
Exercises of common stock warrants	6,918	$ 8	6,910
Issuance of common stock and common stock warrants, net of issuance costs (in shares)		25,555,556
Issuance of common stock and common stock warrants, net of issuance costs	41,932	$ 26	41,906
Ending balance (in shares) at Jun. 30, 2018		77,010,999
Ending balance at Jun. 30, 2018	64,064	$ 77	229,239	(165,252)
Increase (Decrease) in Stockholders' Equity [Roll Forward]
Beginning balance (in shares)		77,010,999
Beginning balance (in shares)		77,088,570
Net loss	(14,015)			(14,015)
Share-based compensation	249		249
Sales of common stock under 2014 ESPP (in shares)		11,427
Sales of common stock under 2014 ESPP	11		11
Exercise of stock options and vesting of restricted stock awards (in shares)		16,144
Exercises of stock options and vestings of restricted stock awards	27		27
Exercises of common stock warrants (in shares)		50,000
Exercises of common stock warrants	59		59
Ending balance (in shares) at Sep. 30, 2018		77,088,570
Ending balance at Sep. 30, 2018	50,395	$ 77	229,585	(179,267)
Increase (Decrease) in Stockholders' Equity [Roll Forward]
Beginning balance (in shares)		77,088,570
Beginning balance (in shares)		77,456,180
Beginning balance (in shares)		77,464,781
Beginning balance at Dec. 31, 2018	44,207	$ 77	230,154	(186,024)
Increase (Decrease) in Stockholders' Equity [Roll Forward]
Net loss	(6,480)			(6,480)
Share-based compensation	326		326
Sales of common stock under 2014 ESPP (in shares)		8,601
Sales of common stock under 2014 ESPP	7		7
Ending balance (in shares) at Mar. 31, 2019		77,464,781
Ending balance at Mar. 31, 2019	38,060	$ 77	230,487	(192,504)
Increase (Decrease) in Stockholders' Equity [Roll Forward]
Beginning balance (in shares)		101,267,578
Beginning balance at Dec. 31, 2018	44,207	$ 77	230,154	(186,024)
Increase (Decrease) in Stockholders' Equity [Roll Forward]
Net loss	$ (73,947)
Exercise of stock options and vesting of restricted stock awards (in shares)	30,000
Exercises of common stock warrants (in shares)	3,361,000	3,400,000
Ending balance (in shares) at Sep. 30, 2019		101,267,578
Ending balance at Sep. 30, 2019	$ 2,467	$ 101	262,337	(259,971)
Increase (Decrease) in Stockholders' Equity [Roll Forward]
Beginning balance (in shares)		77,464,781
Beginning balance (in shares)		101,265,896
Beginning balance at Mar. 31, 2019	38,060	$ 77	230,487	(192,504)
Increase (Decrease) in Stockholders' Equity [Roll Forward]
Net loss	(54,335)			(54,335)
Share-based compensation	356		356
Exercise of stock options and vesting of restricted stock awards (in shares)		30,000
Exercises of stock options and vestings of restricted stock awards	45		45
Exercises of common stock warrants (in shares)		3,361,115
Exercises of common stock warrants	3,434	$ 4	3,430
Issuance of common stock and common stock warrants, net of issuance costs (in shares)		20,410,000
Issuance of common stock and common stock warrants, net of issuance costs	27,809	$ 20	27,789
Ending balance (in shares) at Jun. 30, 2019		101,265,896
Ending balance at Jun. 30, 2019	15,369	$ 101	262,107	(246,839)
Increase (Decrease) in Stockholders' Equity [Roll Forward]
Beginning balance (in shares)		101,265,896
Beginning balance (in shares)		101,267,578
Net loss	(13,132)			(13,132)
Share-based compensation	229		229
Sales of common stock under 2014 ESPP (in shares)		1,682
Sales of common stock under 2014 ESPP	1		1
Ending balance (in shares) at Sep. 30, 2019		101,267,578
Ending balance at Sep. 30, 2019	$ 2,467	$ 101	$ 262,337	$ (259,971)
Increase (Decrease) in Stockholders' Equity [Roll Forward]
Beginning balance (in shares)		101,267,578