Note 17 - Shareholders' Equity and Stock Plans - Stock Option Activity (Details) - USD ($)	12 Months Ended
	Dec. 31, 2018	Dec. 31, 2017	Dec. 31, 2016
Options outstanding (in shares)	134,500	188,900
Options outstanding, weighted average exercise price (in dollars per share)	$ 5.24	$ 5.08
Options outstanding, aggregate intrinsic value	$ 488,665	$ 704,350	$ 834,625
Options outstanding, weighted average remaining contractual term (Year)	4 years 40 days	4 years 277 days	5 years 240 days
Exercised (in shares)	(37,100)	(51,900)
Exercised, weighted average exercise price (in dollars per share)	$ 5.82	$ 4.73
Exercised, aggregate intrinsic value	$ 215,685	$ 245,450
Exercised, weighted average remaining contractual term (Year) (Year)	2 years 350 days	4 years 153 days
Forfeited (in shares)		(2,500)
Forfeited, weighted average exercise price (in dollars per share)		$ 4.05
Options outstanding (in shares)	97,400	134,500	188,900
Options outstanding, weighted average exercise price (in dollars per share)	$ 5.02	$ 5.24	$ 5.08
Exercisable at December 31, 2018 (in shares)	93,400
Exercisable at December 31, 2018 (in dollars per share)	$ 4.98
Exercisable at December 31, 2018	$ 465,345
Exercisable at December 31, 2018 (Year)	4 years 10 days