Condensed Statements of Shareholders' Equity - USD ($) shares in Thousands, $ in Thousands	Common stock	Additional paid-in capital	Accumulated deficit	Total
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	351	0	351
Share-based compensation expense, shares	0
Sales of common stock	$ 2	1,166	0	1,168
Sales of common stock, shares	2,000
Net loss	$ 0	0	(8,068)	(8,068)
Ending balances at Mar. 31, 2019	$ 102	551,650	(554,184)	(2,432)
Ending balances, shares at Mar. 31, 2019	102,105
Beginning balances at Dec. 31, 2019	$ 126	568,496	(572,599)	(3,977)
Beginning balances, shares at Dec. 31, 2019	125,803
Share-based compensation expense	$ 0	156	0	156
Share-based compensation expense, shares	0
Sales of common stock	$ 5	1,476	0	1,481
Sales of common stock, shares	5,075
Net loss	$ 0	0	(4,934)	(4,934)
Ending balances at Mar. 31, 2020	$ 131	$ 570,128	$ (577,533)	$ (7,274)
Ending balances, shares at Mar. 31, 2020	130,878