Note 7 - Shareholders' Equity - Stock Option Activity (Details) - USD ($) $ / shares in Units, $ in Thousands	12 Months Ended
	Dec. 31, 2020	Dec. 31, 2019
Shares under Option, beginning of period (in shares)	1,541,792	1,576,087
Options outstanding - weighted average exercise price (in dollars per share)	$ 6.88	$ 6.58
Options granted (in shares)	256,000	282,500
Options granted - weighted average exercise price (in dollars per share)	$ 6.51	$ 8.27
Options exercised (in shares)	(355,797)	(208,881)
Options exercised - weighted average exercise price (in dollars per share)	$ 6.08	$ 4.45
Options forfeited or expired (in shares)	(224,332)	(107,914)
Options forfeited or expired - weighted average exercise price (in dollars per share)	$ 9.76	$ 10.93
Shares under option, end 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 outstanding - weighted average remaining contractual term (Year)	3 years 11 months 19 days
Options outstanding - aggregate intrinsic value	$ 1,034
Vested and Expected to Vest (in shares)	1,115,705
Options vested and expected to vest - weighted average exercise price (in dollars per share)	$ 6.39
Options vested and expected to vest - weighted average remaining contractual term (Year)	3 years 9 months 21 days
Options vested and expected to vest - aggregate intrinsic value	$ 1,034
Options Exercisable (in shares)	738,452	1,083,581
Options exercisable, weighted-average exercise price (in dollars per share)	$ 5.82	$ 6.28
Options exercisable - weighted average remaining contractual term (Year)	2 years 9 months 14 days
Options exercisable - aggregate intrinsic value	$ 1,034