Note 2 - Investment Securities (Details) - Amortized Cost and Fair Values of General Obligation Bonds by Issuer's State	Mar. 31, 2016 USD ($)	Dec. 31, 2015 USD ($)
General Obligation Bonds [Member]
Note 2 - Investment Securities (Details) - Amortized Cost and Fair Values of General Obligation Bonds by Issuer's State [Line Items]
Number of issuers	82	82
Amortized cost	$ 71,391,381	$ 66,683,832
Fair value	72,662,999	67,778,032
Average exposure per issuer (fair value)	$ 886,134	$ 826,561
General Obligation Bonds [Member] | IOWA
Note 2 - Investment Securities (Details) - Amortized Cost and Fair Values of General Obligation Bonds by Issuer's State [Line Items]
Number of issuers	15	15
Amortized cost	$ 19,974,438	$ 19,974,939
Fair value	20,309,435	20,247,108
Average exposure per issuer (fair value)	$ 1,353,962	$ 1,349,807
General Obligation Bonds [Member] | ILLINOIS
Note 2 - Investment Securities (Details) - Amortized Cost and Fair Values of General Obligation Bonds by Issuer's State [Line Items]
Number of issuers	10	9
Amortized cost	$ 12,665,888	$ 10,928,700
Fair value	13,014,865	11,264,348
Average exposure per issuer (fair value)	$ 1,301,487	$ 1,251,594
General Obligation Bonds [Member] | MISSOURI
Note 2 - Investment Securities (Details) - Amortized Cost and Fair Values of General Obligation Bonds by Issuer's State [Line Items]
Number of issuers	12	12
Amortized cost	$ 7,393,378	$ 7,924,800
Fair value	7,488,699	7,986,856
Average exposure per issuer (fair value)	$ 624,058	$ 665,571
General Obligation Bonds [Member] | NORTH DAKOTA
Note 2 - Investment Securities (Details) - Amortized Cost and Fair Values of General Obligation Bonds by Issuer's State [Line Items]
Number of issuers	6	5
Amortized cost	$ 16,403,026	$ 10,890,000
Fair value	16,616,824	11,050,235
Average exposure per issuer (fair value)	$ 2,769,471	$ 2,210,047
General Obligation Bonds [Member] | Other States [Member]
Note 2 - Investment Securities (Details) - Amortized Cost and Fair Values of General Obligation Bonds by Issuer's State [Line Items]
Number of issuers	39	41
Amortized cost	$ 14,954,651	$ 16,965,393
Fair value	15,233,176	17,229,485
Average exposure per issuer (fair value)	$ 390,594	$ 420,231
Revenue Bonds [Member]
Note 2 - Investment Securities (Details) - Amortized Cost and Fair Values of General Obligation Bonds by Issuer's State [Line Items]
Number of issuers	95	92
Amortized cost	$ 212,801,978	$ 212,705,308
Fair value	215,631,378	214,441,841
Average exposure per issuer (fair value)	$ 2,269,804	$ 2,330,890
Revenue Bonds [Member] | IOWA
Note 2 - Investment Securities (Details) - Amortized Cost and Fair Values of General Obligation Bonds by Issuer's State [Line Items]
Number of issuers	27	26
Amortized cost	$ 74,013,142	$ 70,773,660
Fair value	75,274,793	71,659,410
Average exposure per issuer (fair value)	$ 2,787,955	$ 2,756,131
Revenue Bonds [Member] | MISSOURI
Note 2 - Investment Securities (Details) - Amortized Cost and Fair Values of General Obligation Bonds by Issuer's State [Line Items]
Number of issuers	42	41
Amortized cost	$ 76,260,706	$ 78,593,590
Fair value	77,142,220	79,015,378
Average exposure per issuer (fair value)	$ 1,836,720	$ 1,927,204
Revenue Bonds [Member] | Other States [Member]
Note 2 - Investment Securities (Details) - Amortized Cost and Fair Values of General Obligation Bonds by Issuer's State [Line Items]
Number of issuers	5	5
Amortized cost	$ 11,162,489	$ 11,570,998
Fair value	11,422,830	11,735,678
Average exposure per issuer (fair value)	$ 2,284,566	$ 2,347,136
Revenue Bonds [Member] | INDIANA
Note 2 - Investment Securities (Details) - Amortized Cost and Fair Values of General Obligation Bonds by Issuer's State [Line Items]
Number of issuers	17	17
Amortized cost	$ 39,342,789	$ 40,018,381
Fair value	39,675,326	40,210,320
Average exposure per issuer (fair value)	$ 2,333,843	$ 2,365,313
Revenue Bonds [Member] | KANSAS
Note 2 - Investment Securities (Details) - Amortized Cost and Fair Values of General Obligation Bonds by Issuer's State [Line Items]
Number of issuers	4	3
Amortized cost	$ 12,022,852	$ 11,748,679
Fair value	12,116,209	11,821,055
Average exposure per issuer (fair value)	$ 3,029,052	$ 3,940,352