Note 8 - Income Taxes - Provision for Income Taxes (Details) - USD ($)	12 Months Ended
	Dec. 31, 2017	Dec. 31, 2016	Dec. 31, 2015
Current provision:
Federal	$ 3,090,997	$ 3,108,894	$ 3,045,292
State	309,249	486,565	482,186
Total current income tax expense	3,400,246	3,595,459	3,527,478
Deferred provision (benefit):
Federal	(665,181)	183,520	212,563
State	(23,692)	21,591	76,607
Total deferred income tax expense	(688,873)	205,111	289,170
Total income tax expense	$ 2,711,373	$ 3,800,570	$ 3,816,648