CONSOLIDATED STATEMENTS OF STOCKHOLDERS' EQUITY - 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]
Exercise of stock options and vesting of restricted stock awards (in shares)		4,430
Exercise of stock options and vesting of restricted stock awards	0
Issuance of common stock pursuant to the 2014 ESPP (in shares)		9,565
Issuance of common stock pursuant to the 2014 ESPP	10		10
Exercise of common stock warrants (in shares)		420,778
Exercise 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
Stock-based compensation expense	401		401
Net loss	(3,963)			(3,963)
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)		77,010,999
Beginning balance at Dec. 31, 2017	18,034	$ 35	170,330	(152,331)
Increase (Decrease) in Stockholders' Equity [Roll Forward]
Net loss	(12,921)
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)		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]
Exercise of stock options and vesting of restricted stock awards (in shares)		55,259
Exercise of stock options and vesting of restricted stock awards	29		29
Exercise of common stock warrants (in shares)		8,294,718
Exercise 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
Stock-based compensation expense	285		285
Net loss	(8,958)			(8,958)
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)		77,456,180
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]
Issuance of common stock pursuant to the 2014 ESPP (in shares)		8,601
Issuance of common stock pursuant to the 2014 ESPP	7		7
Stock-based compensation expense	326		326
Net loss	(6,480)			(6,480)
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)		101,265,896
Beginning balance at Dec. 31, 2018	$ 44,207	$ 77	230,154	(186,024)
Increase (Decrease) in Stockholders' Equity [Roll Forward]
Exercise of stock options and vesting of restricted stock awards (in shares)	30,000
Exercise of common stock warrants (in shares)	3,361,115
Net loss	$ (60,815)
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)		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]
Exercise of stock options and vesting of restricted stock awards (in shares)		30,000
Exercise of stock options and vesting of restricted stock awards	$ 45		45
Exercise of common stock warrants (in shares)	3,400,000	3,361,115
Exercise 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
Stock-based compensation expense	356		356
Net loss	(54,335)			(54,335)
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