Condensed Consolidated Statements of Shareholders' Equity (Deficit) - USD ($) shares in Thousands, $ in Thousands	Common stock	Additional paid-in capital	Accumulated deficit	Total
Beginning balances at Dec. 31, 2017	$ 79	$ 528,873	$ (524,086)	$ 4,866
Beginning balances, shares at Dec. 31, 2017	78,597
Adoption of New Accounting Pronouncement, Revenue from Contracts with Customers	$ 0	0	5,220	5,220
Share-based compensation expense	$ 0	724	0	724
Share-based compensation expense, shares	76
Sales of common stock	$ 14	16,526	0	16,540
Sales of common stock, shares	14,400
Net income (loss)	$ 0	0	(15,302)	(15,302)
Ending balances at Sep. 30, 2018	$ 93	546,123	(534,168)	12,048
Ending balances, shares at Sep. 30, 2018	93,073
Beginning balances at Jun. 30, 2018	$ 93	545,978	(534,457)	11,614
Beginning balances, shares at Jun. 30, 2018	93,073
Share-based compensation expense	$ 0	181	0	181
Share-based compensation expense, shares	0
Sales of common stock	$ 0	(36)	0	(36)
Sales of common stock, shares	0
Net income (loss)	$ 0	0	289	289
Ending balances at Sep. 30, 2018	$ 93	546,123	(534,168)	12,048
Ending balances, shares at Sep. 30, 2018	93,073
Beginning balances at Dec. 31, 2018	$ 100	550,133	(546,116)	4,117
Beginning balances, shares at Dec. 31, 2018	100,105
Share-based compensation expense	$ 0	877	0	877
Share-based compensation expense, shares	250
Sales of common stock	$ 19	13,217	0	13,236
Sales of common stock, shares	19,062
Net income (loss)	$ 0	0	(23,199)	(23,199)
Ending balances at Sep. 30, 2019	$ 119	564,227	(569,315)	(4,969)
Ending balances, shares at Sep. 30, 2019	119,417
Beginning balances at Jun. 30, 2019	$ 110	558,334	(563,174)	(4,730)
Beginning balances, shares at Jun. 30, 2019	110,223
Share-based compensation expense	$ 0	258	0	258
Share-based compensation expense, shares	0
Sales of common stock	$ 9	5,635	0	5,644
Sales of common stock, shares	9,194
Net income (loss)	$ 0	0	(6,141)	(6,141)
Ending balances at Sep. 30, 2019	$ 119	$ 564,227	$ (569,315)	$ (4,969)
Ending balances, shares at Sep. 30, 2019	119,417