Consolidated Statements of Shareholders' Equity - USD ($) shares in Thousands, $ in Thousands	Common stock	Additional paid-in capital	Accumulated deficit	Total
Beginning balances at Dec. 31, 2014	$ 45	$ 475,656	$ (468,829)	$ 6,872
Beginning balances, shares at Dec. 31, 2014	44,758
Share-based compensation expense	$ 0	1,011	0	1,011
Share-based compensation expense, shares	86
Sales of common stock and warrants	$ 1	3,205	0	3,206
Sales of common stock and warrants, shares	1,069
Exchange of warrants				0
Exercise of warrants and options	$ 1	3,299	0	3,300
Exercise of warrants and options, shares	1,510
Net loss	$ 0	0	(14,542)	(14,542)
Ending balances at Dec. 31, 2015	$ 47	483,171	(483,371)	(153)
Ending balances, shares at Dec. 31, 2015	47,423
Share-based compensation expense	$ 0	1,223	0	1,223
Share-based compensation expense, shares	87
Exercise of options	$ 0	7	0	7
Exercise of options, shares	4
Sales of common stock and warrants	$ 21	22,848	0	22,869
Sales of common stock and warrants, shares	20,579
Net loss	$ 0	0	(16,472)	(16,472)
Ending balances at Dec. 31, 2016	$ 68	507,249	(499,843)	7,474
Ending balances, shares at Dec. 31, 2016	68,093
Share-based compensation expense	$ 0	1,288	0	1,288
Share-based compensation expense, shares	92
Sales of common stock and warrants	$ 11	19,345	0	19,356
Sales of common stock and warrants, shares	9,906
Exercise of warrants and options	$ 0	991	0	991
Exercise of warrants and options, shares	506
Net loss	$ 0	0	(24,243)	(24,243)
Ending balances at Dec. 31, 2017	$ 79	$ 528,873	$ (524,086)	$ 4,866
Ending balances, shares at Dec. 31, 2017	78,597