Condensed Statements of Shareholders' Equity (Deficit) - USD ($) shares in Thousands, $ in Thousands	Common stock	Additional paid-in capital	Subscriptions receivable	Accumulated deficit	Total
Beginning balances at Dec. 31, 2019	$ 126	$ 568,496	$ 0	$ (572,599)	$ (3,977)
Beginning balances, shares at Dec. 31, 2019	125,803
Share-based compensation expense	$ 0	156	0	0	156
Share-based compensation expense, shares	0
Sales of common stock	$ 5	1,476	0	0	1,481
Sales of common stock, shares	5,075
Net loss	$ 0	0	0	(4,934)	(4,934)
Ending balances at Mar. 31, 2020	$ 131	570,128	0	(577,533)	(7,274)
Ending balances, shares at Mar. 31, 2020	130,878
Beginning balances at Dec. 31, 2020	$ 153	601,224	(6,135)	(586,233)	9,009
Beginning balances, shares at Dec. 31, 2020	152,926
Share-based compensation expense	$ 0	1,638	0	0	1,638
Share-based compensation expense, shares	368
Exercise of options	$ 1	2,080	0	0	2,081
Exercise of options, shares	1,071
Sales of common stock	$ 4	55,325	6,135	0	61,464
Sales of common stock, shares	3,587
Net loss	$ 0	0	0	(6,231)	(6,231)
Ending balances at Mar. 31, 2021	$ 158	$ 660,267	$ 0	$ (592,464)	$ 67,961
Ending balances, shares at Mar. 31, 2021	157,952