Note 16 - Shareholders' Equity and Stock Plans - Stock Option Activity (Details) - USD ($)	12 Months Ended
	Dec. 31, 2019	Dec. 31, 2018	Dec. 31, 2017
Options outstanding (in shares)	97,400	134,500
Options outstanding, weighted average exercise price (in dollars per share)	$ 5.02	$ 5.24
Options outstanding, aggregate intrinsic value	$ 436,995	$ 488,665	$ 704,350
Options outstanding, weighted average remaining contractual term (Year)	3 years 32 days	4 years 40 days	4 years 277 days
Exercised (in shares)	(11,000)	(37,100)
Exercised, weighted average exercise price (in dollars per share)	$ 4.70	$ 5.82
Exercised, aggregate intrinsic value	$ 51,670	$ 215,685
Options outstanding (in shares)	86,400	97,400	134,500
Options outstanding, weighted average exercise price (in dollars per share)	$ 5.06	$ 5.02	$ 5.24
Exercisable (in shares)	86,400	93,400
Exercisable, weighted average exercise price (in dollars per share)	$ 5.06	$ 5.02
Exercisable, aggregate intrinsic value	$ 436,995	$ 488,665
Exercisable, weighted average remaining contractual term (Year) (Year)	3 years 32 days	4 years 40 days