Note 3 - Investment Securities - Amortized Cost and Fair Values of General Obligation Bonds and Revenue Bonds by Issuer's State (Details)	Dec. 31, 2016 USD ($)	Dec. 31, 2015 USD ($)
General Obligation Bonds [Member]
Number of issuers	116	82
Amortized cost	$ 117,205,307	$ 66,683,832
Other Investments	116,472,635	67,778,032
Average exposure per issuer (fair value)	$ 1,004,074	$ 826,561
General Obligation Bonds [Member] | Iowa [Member]
Number of issuers	27	15
Amortized cost	$ 32,258,612	$ 19,974,939
Other Investments	32,231,936	20,247,108
Average exposure per issuer (fair value)	$ 1,193,775	$ 1,349,807
General Obligation Bonds [Member] | Missouri [Member]
Number of issuers	14	12
Amortized cost	$ 8,291,192	$ 7,924,800
Other Investments	8,323,245	7,986,856
Average exposure per issuer (fair value)	$ 594,518	$ 665,571
General Obligation Bonds [Member] | Illinois [Member]
Number of issuers	19	9
Amortized cost	$ 29,214,559	$ 10,928,700
Other Investments	29,308,438	11,264,348
Average exposure per issuer (fair value)	$ 1,542,549	$ 1,251,594
General Obligation Bonds [Member] | North Dakota [Member]
Number of issuers	7	5
Amortized cost	$ 22,169,050	$ 10,890,000
Other Investments	21,499,075	11,050,235
Average exposure per issuer (fair value)	$ 3,071,296	$ 2,210,047
General Obligation Bonds [Member] | Ohio [Member]
Number of issuers	8
Amortized cost	$ 6,790,398
Other Investments	6,651,897
Average exposure per issuer (fair value)	$ 831,487
General Obligation Bonds [Member] | Other States [Member]
Number of issuers	41	41
Amortized cost	$ 18,481,496	$ 16,965,393
Other Investments	18,458,044	17,229,485
Average exposure per issuer (fair value)	$ 450,196	$ 420,231
Revenue Bonds [Member]
Number of issuers	120	92
Amortized cost	$ 257,470,290	$ 212,705,308
Other Investments	255,496,690	214,441,841
Average exposure per issuer (fair value)	$ 2,129,139	$ 2,330,890
Revenue Bonds [Member] | Iowa [Member]
Number of issuers	31	26
Amortized cost	$ 70,788,393	$ 70,773,660
Other Investments	71,142,393	71,659,410
Average exposure per issuer (fair value)	$ 2,294,916	$ 2,756,131
Revenue Bonds [Member] | Missouri [Member]
Number of issuers	47	41
Amortized cost	$ 90,784,441	$ 78,593,590
Other Investments	89,664,013	79,015,378
Average exposure per issuer (fair value)	$ 1,907,745	$ 1,927,204
Revenue Bonds [Member] | North Dakota [Member]
Number of issuers	4
Amortized cost	$ 8,089,067
Other Investments	7,796,381
Average exposure per issuer (fair value)	$ 1,949,095
Revenue Bonds [Member] | Indiana [Member]
Number of issuers	22	17
Amortized cost	$ 47,994,737	$ 40,018,381
Other Investments	47,582,138	40,210,320
Average exposure per issuer (fair value)	$ 2,162,824	$ 2,365,313
Revenue Bonds [Member] | Kansas [Member]
Number of issuers	6	3
Amortized cost	$ 13,476,366	$ 11,748,679
Other Investments	13,427,491	11,821,055
Average exposure per issuer (fair value)	$ 2,237,915	$ 3,940,352
Revenue Bonds [Member] | Ohio [Member]
Number of issuers	3
Amortized cost	$ 13,650,000
Other Investments	13,405,222
Average exposure per issuer (fair value)	$ 4,468,407
Revenue Bonds [Member] | Other States [Member]
Number of issuers	7	5
Amortized cost	$ 12,687,286	$ 11,570,998
Other Investments	12,479,052	11,735,678
Average exposure per issuer (fair value)	$ 1,782,722	$ 2,347,136