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, 2016	$ 68	$ 507,249	$ (493,380)	$ 13,937
Beginning balances, shares at Dec. 31, 2016	68,093
Share-based compensation expense	$ 0	1,288	0	$ 1,288
Share-based compensation expense, shares	92
Exercise of options, shares				46
Sales of common stock	$ 11	19,345	0	$ 19,356
Sales of common stock, shares	9,906
Exercise of warrants and options	$ 0	991	0	991
Exercise of warrants and options, shares	506
Net loss	$ 0	0	(25,486)	(25,486)
Ending balances at Dec. 31, 2017	$ 79	528,873	(518,866)	10,086
Ending balances, shares at Dec. 31, 2017	78,597
Share-based compensation expense	$ 0	1,061	0	$ 1,061
Share-based compensation expense, shares	108
Exercise of options, shares				0
Sales of common stock	$ 21	20,199	0	$ 20,220
Sales of common stock, shares	21,400
Net loss	$ 0	0	(27,250)	(27,250)
Ending balances at Dec. 31, 2018	$ 100	$ 550,133	$ (546,116)	$ 4,117
Ending balances, shares at Dec. 31, 2018	100,105