Condensed Consolidated Statements of Stockholders' Equity - USD ($) $ in Thousands	Total	Common Stock	Additional Paid-In Capital	Treasury Stock	Accumulated Deficit	Series A Preferred Stock	Series B Preferred Stock
Beginning Balance at Dec. 31, 2017	$ 8,877	$ 56	$ 313,922	$ (47)	$ (305,056)	$ 2	$ 0
Beginning Balance (in shares) at Dec. 31, 2017		55,904,072				2,093,155	0
Stock-based compensation	4,896		4,896
Stock option exercises	528		528
Stock option exercises (in shares)		285,403
Restricted stock awards	0	$ 2	(2)
Restricted stock awards (in shares)		1,733,731
Common stock issuance upon retirement	0	$ 2	(2)
Common stock issuance upon retirement (in shares)		2,119,925
Series B issuance, net of issuance costs (in shares)							5,000
Series B issuance, net of issuance cost	47,993		47,993
Series B conversion to common stock	0	$ 11	(11)
Series B conversion to common stock (in shares)		10,555,556					(1,900)
Cumulative effect of accounting change	135				135
Series B beneficial conversion feature	0		12,500		(12,500)
Net income (loss)	(26,859)				(26,859)
Ending Balance at Sep. 30, 2018	35,570	$ 71	379,824	(47)	(344,280)	$ 2	$ 0
Ending Balance (in shares) at Sep. 30, 2018		70,598,687				2,093,155	3,100
Beginning Balance at Jun. 30, 2018	40,737	$ 59	366,123	(47)	(325,400)	$ 2	$ 0
Beginning Balance (in shares) at Jun. 30, 2018		59,459,446				2,093,155	5,000
Stock-based compensation	892		892
Stock option exercises	222		222
Stock option exercises (in shares)		116,387
Restricted stock awards	0	$ 1	(1)
Restricted stock awards (in shares)		467,298
Series B issuance, net of issuance cost	99		99
Series B conversion to common stock	0	$ 11	(11)
Series B conversion to common stock (in shares)		10,555,556					(1,900)
Cumulative effect of accounting change	0
Series B beneficial conversion feature			12,500		(12,500)
Net income (loss)	(6,380)				(6,380)
Ending Balance at Sep. 30, 2018	35,570	$ 71	379,824	(47)	(344,280)	$ 2	$ 0
Ending Balance (in shares) at Sep. 30, 2018		70,598,687				2,093,155	3,100
Beginning Balance at Dec. 31, 2018	29,742	$ 71	381,004	(47)	(351,288)	$ 2	$ 0
Beginning Balance (in shares) at Dec. 31, 2018		70,793,725				2,093,155	3,100
Stock-based compensation	3,978		3,978
Stock option exercises	$ 1,193		1,193
Stock option exercises (in shares)	412,500	412,500
Restricted stock awards	$ 0	$ 1	(1)
Restricted stock awards (in shares)		801,661
Series B issuance, net of issuance costs (in shares)						0
Series B conversion to common stock	0	$ 8	(8)
Series B conversion to common stock (in shares)		7,788,888					(1,402)
Equity offering, net of finance costs	47,590	$ 10	47,580
Equity offering, net of finance costs (in shares)		10,000,000
Net income (loss)	(14,609)				(14,609)
Ending Balance at Sep. 30, 2019	67,894	$ 90	433,746	(47)	(365,897)	$ 2	$ 0
Ending Balance (in shares) at Sep. 30, 2019		89,796,774				2,093,155	1,698
Beginning Balance at Jun. 30, 2019	66,150	$ 88	432,358	(47)	(366,251)	$ 2	$ 0
Beginning Balance (in shares) at Jun. 30, 2019		89,535,024				2,093,155	1,716
Stock-based compensation	1,267		1,267
Stock option exercises	123		123
Stock option exercises (in shares)		52,121
Restricted stock awards	0	$ 2	(2)
Restricted stock awards (in shares)		109,629
Series B conversion to common stock (in shares)		100,000					(18)
Net income (loss)	354				354
Ending Balance at Sep. 30, 2019	$ 67,894	$ 90	$ 433,746	$ (47)	$ (365,897)	$ 2	$ 0
Ending Balance (in shares) at Sep. 30, 2019		89,796,774				2,093,155	1,698