Condensed Consolidated Statements of Stockholders' Equity - USD ($)	Total	Common Stock [Member]	Additional Paid-In Capital [Member]	Treasury Stock [Member]	Accumulated Deficit [Member]	Series A Preferred Stock [Member]	Series B Preferred Stock [Member]
Beginning Balance at Dec. 31, 2017	$ 8,877,000	$ 56,000	$ 313,922,000	$ (47,000)	$ (305,056,000)	$ 2,000
Beginning Balance, shares at Dec. 31, 2017		55,904,072				2,093,155
Stock-based compensation	4,004,000		4,004,000
Stock-based compensation, shares		0				0	0
Stock option exercises	306,000		306,000
Stock option exercises, shares		169,016
Restricted stock awards		$ 1,000	(1,000)
Restricted stock awards, shares		1,266,433
Common stock issuance upon retirement		$ 2,000	(2,000)
Common stock issuance upon retirement, shares		2,119,925
Series B conversion to common stock	47,894,000		47,894,000
Series B conversion to common stock, shares							5,000
Cumulative effect of accounting change	135,000				135,000
Net loss	(20,479,000)				(20,479,000)
Ending Balance at Jun. 30, 2018	40,737,000	$ 59,000	366,123,000	(47,000)	(325,400,000)	$ 2,000
Ending Balance, shares at Jun. 30, 2018		59,459,446				2,093,155	5,000
Beginning Balance at Mar. 31, 2018	1,354,000	$ 59,000	316,970,000	(47,000)	(315,630,000)	$ 2,000
Beginning Balance, shares at Mar. 31, 2018		55,646,522				2,093,155
Stock-based compensation	1,083,000		1,083,000
Stock-based compensation, shares		0				0	0
Stock option exercises	$ 176,000		$ 176,000
Stock option exercises, shares		105,721
Restricted stock awards, shares		227,476
Common stock issuance upon retirement, shares		479,727
Series B conversion to common stock							$ (684)
Series B conversion to common stock, shares	47,894,000		47,894,000
Cumulative effect of accounting change	$ 135,000				135,000
Net loss	(9,770,000)				(9,770,000)
Ending Balance at Jun. 30, 2018	40,737,000	$ 59,000	$ 366,123,000	(47,000)	(325,400,000)	$ 2,000
Ending Balance, shares at Jun. 30, 2018		59,459,446				2,093,155	5,000
Beginning Balance at Dec. 31, 2018	29,742,000	$ 71,000	381,004,000	(47,000)	(351,288,000)	$ 2,000
Beginning Balance, shares at Dec. 31, 2018		70,793,725				2,093,155	3,100
Stock-based compensation	2,711,000		2,711,000
Stock-based compensation, shares		0				0	0
Stock option exercises	$ 1,070,000		1,070,000
Stock option exercises, shares	360,379	360,379
Restricted stock awards		$ (1,000)	1,000
Restricted stock awards, shares		692,032
Series B conversion to common stock		$ 8,000	(8,000)
Series B conversion to common stock, shares		7,688,888				0	(1,384)
Equity offering, net of finance costs	$ 47,590,000	$ 10,000	47,580,000
Equity offering, net of finance costs, shares		10,000,000
Series B issuance, net of issuance costs, shares						0
Net loss	(14,963,000)				(14,963,000)
Ending Balance at Jun. 30, 2019	66,150,000	$ 88,000	432,358,000	(47,000)	(366,251,000)	$ 2,000
Ending Balance, shares at Jun. 30, 2019		89,535,024				2,093,155	1,716
Beginning Balance at Mar. 31, 2019	27,522,000	$ 74,000	382,614,000	(47,000)	(355,121,000)	$ 2,000
Beginning Balance, shares at Mar. 31, 2019		75,333,254				2,093,155	2,400
Stock-based compensation	1,570,000		1,570,000
Stock-based compensation, shares		0				0	0
Stock option exercises	598,000		598,000
Stock option exercises, shares		210,104
Restricted stock awards, shares		191,666
Series B conversion to common stock		$ 4,000	(4,000)
Series B conversion to common stock, shares		3,800,000					(684)
Equity offering, net of finance costs	47,590,000	$ 10,000	47,580,000
Equity offering, net of finance costs, shares		10,000,000
Net loss	(11,130,000)				(11,130,000)
Ending Balance at Jun. 30, 2019	$ 66,150,000	$ 88,000	$ 432,358,000	$ (47,000)	$ (366,251,000)	$ 2,000
Ending Balance, shares at Jun. 30, 2019		89,535,024				2,093,155	1,716