Note 10 - Income Taxes - The Provision for Income Taxes (Details) - USD ($)	3 Months Ended								12 Months Ended
	Dec. 31, 2017	Sep. 30, 2017	Jun. 30, 2017	Mar. 31, 2017	Dec. 31, 2016	Sep. 30, 2016	Jun. 30, 2016	Mar. 31, 2016	Dec. 31, 2017	Dec. 31, 2016	Dec. 31, 2015
Taxes currently payable									$ 1,490,297	$ 1,889,673	$ 2,140,591
Deferred income taxes									1,080,452	123,091	320,738
Deferred income taxes related to 2017 Tax Act									1,012,112
	$ 1,102,883	$ 443,651	$ 520,770	$ 503,445	$ 514,981	$ 554,009	$ 416,399	$ 527,375	$ 2,570,749	$ 2,012,764	$ 2,461,329