Note 6 - Shareholders' Equity - Stock Option Activity (Details) - USD ($) $ / shares in Units, $ in Thousands	12 Months Ended
	Dec. 31, 2021	Dec. 31, 2020
Shares under Option, beginning of period (in shares)	1,217,163	1,541,792
Options outstanding - weighted average exercise price (in dollars per share)	$ 6.50	$ 6.88
Options granted (in shares)	340,500	256,000
Options granted - weighted average exercise price (in dollars per share)	$ 6.78	$ 6.51
Options exercised (in shares)	(204,429)	(355,797)
Options exercised - weighted average exercise price (in dollars per share)	$ 4.39	$ 6.08
Options forfeited or expired (in shares)	(46,410)	(224,832)
Options forfeited or expired - weighted average exercise price (in dollars per share)	$ 7.44	$ 9.76
Shares under option, end of period (in shares)	1,306,824	1,217,163
Options outstanding - weighted average exercise price (in dollars per share)	$ 6.87	$ 6.50
Options outstanding - weighted average remaining contractual term (Year)	4 years 2 months 19 days
Options outstanding - aggregate intrinsic value	$ 504
Vested and Expected to Vest (in shares)	1,189,175
Options vested and expected to vest - weighted average exercise price (in dollars per share)	$ 6.86
Options vested and expected to vest - weighted average remaining contractual term (Year)	4 years 18 days
Options vested and expected to vest - aggregate intrinsic value	$ 492
Options Exercisable (in shares)	745,288	738,452
Options exercisable, weighted-average exercise price (in dollars per share)	$ 6.85	$ 5.82
Options exercisable - weighted average remaining contractual term (Year)	2 years 9 months 18 days
Options exercisable - aggregate intrinsic value	$ 439