Note 6 - Leases - Lease Expense (Details) - USD ($)	3 Months Ended		6 Months Ended
	Jun. 30, 2021	Jun. 30, 2020	Jun. 30, 2021	Jun. 30, 2020
Amortization of right-of-use assets	$ 38,673	$ 31,132	$ 83,330	$ 62,109
Interest on lease liabilities	1,683	1,943	3,379	4,039
Operating lease cost	273,351	272,108	545,896	544,443
Sublease income	(6,300)	(12,300)	(12,600)	(24,600)
Total lease costs	$ 307,407	$ 292,883	$ 620,005	$ 585,991
Weighted-average remaining lease term - financing leases (in years) (Year)	3 years 4 months 24 days	3 years	3 years 4 months 24 days	3 years
Weighted-average remaining lease term - operating leases (in years) (Year)	13 years 10 months 24 days	14 years 8 months 12 days	13 years 10 months 24 days	14 years 8 months 12 days
Weighted-average discount rate - financing leases	1.14%	1.95%	1.14%	1.95%
Weighted-average discount rate - operating leases	5.71%	5.64%	5.71%	5.64%