Note 2 - Securities - Securities in a Continuous Unrealized Loss Position (Details) - USD ($)	Dec. 31, 2017	Dec. 31, 2016
Securities, continuous unrealized loss position, less than 12 months, fair value	$ 31,113,287	$ 74,651,451
Securities, continuous unrealized loss position, less than 12 months, unrealized losses	(357,654)	(2,108,360)
Securities, continuous unrealized loss position, 12 months or more, fair value	30,994,373	4,709,778
Securities, continuous unrealized loss position, 12 months or more, unrealized losses	(814,880)	(108,845)
Available-for-sale Securities, Continuous Unrealized Loss Position, Fair Value	62,107,660	79,361,229
Securities, continuous unrealized loss position, unrealized losses	(1,172,534)	(2,217,205)
US States and Political Subdivisions Debt Securities [Member]
Securities, continuous unrealized loss position, less than 12 months, fair value	11,024,593	33,084,816
Securities, continuous unrealized loss position, less than 12 months, unrealized losses	(103,747)	(1,082,021)
Securities, continuous unrealized loss position, 12 months or more, fair value	8,802,796	179,402
Securities, continuous unrealized loss position, 12 months or more, unrealized losses	(159,874)	(3,633)
Available-for-sale Securities, Continuous Unrealized Loss Position, Fair Value	19,827,389	33,264,218
Securities, continuous unrealized loss position, unrealized losses	(263,621)	(1,085,654)
Mortgage-backed Securities, Issued by US Government Sponsored Enterprises [Member]
Securities, continuous unrealized loss position, less than 12 months, fair value	20,088,694	39,570,463
Securities, continuous unrealized loss position, less than 12 months, unrealized losses	(253,907)	(1,022,511)
Securities, continuous unrealized loss position, 12 months or more, fair value	22,191,577	3,649,276
Securities, continuous unrealized loss position, 12 months or more, unrealized losses	(655,006)	(104,526)
Available-for-sale Securities, Continuous Unrealized Loss Position, Fair Value	42,280,271	43,219,739
Securities, continuous unrealized loss position, unrealized losses	$ (908,913)	(1,127,037)
Corporate Debt Securities [Member]
Securities, continuous unrealized loss position, less than 12 months, fair value		1,996,172
Securities, continuous unrealized loss position, less than 12 months, unrealized losses		(3,828)
Securities, continuous unrealized loss position, 12 months or more, fair value		881,100
Securities, continuous unrealized loss position, 12 months or more, unrealized losses		(686)
Available-for-sale Securities, Continuous Unrealized Loss Position, Fair Value		2,877,272
Securities, continuous unrealized loss position, unrealized losses		$ (4,514)