Note 11 - Stock-based Compensation - Stock Option Activity (Details) - USD ($) $ / shares in Units, shares in Thousands, $ in Thousands	12 Months Ended
	Dec. 31, 2021	Dec. 31, 2020	Dec. 31, 2019
Outstanding, stock options (in shares)	7,503	8,013
Outstanding, weighted average exercise price (in dollars per share)	$ 0.54	$ 0.54
Outstanding, weighted average remaining contractual life (Year)	7 years 6 months	8 years 6 months	8 years 6 months
Outstanding, aggregate intrinsic value	$ 0	$ 0
Options granted, stock options (in shares)	80	50
Options granted, weighted average exercise price (in dollars per share)	$ 0.44	$ 0.44
Options granted, weighted average remaining contractual life (Year)	10 years	10 years
Options forfeited/expired, stock options (in shares)	(460)	(560)
Options forfeited/expired, weighted average exercise price (in dollars per share)	$ 0.44	$ 0.63
Outstanding, stock options (in shares)	7,123	7,503	8,013
Outstanding, weighted average exercise price (in dollars per share)	$ 0.54	$ 0.54	$ 0.54
Options vested and exercisable, stock options (in shares)	5,376
Options vested and exercisable, weighted average exercise price (in dollars per share)	$ 0.57
Options vested and exercisable, weighted average remaining contractual life (Year)	7 years 3 months 18 days
Options vested and exercisable, aggregate instrinsic value	$ 0