Note 2 - Investment Securities - Amortized Cost and Fair Values of General Obligation Bonds by Issuer's State (Details)	Sep. 30, 2016 USD ($)	Dec. 31, 2015 USD ($)
General Obligation Bonds [Member] | Iowa [Member]
Number of issuers	27	15
Amortized cost	$ 32,289,974	$ 19,974,939
Other Investments	32,746,465	20,247,108
Average exposure per issuer (fair value)	$ 1,212,832	$ 1,349,807
General Obligation Bonds [Member] | Missouri [Member]
Number of issuers	13	12
Amortized cost	$ 8,304,022	$ 7,924,800
Other Investments	8,448,994	7,986,856
Average exposure per issuer (fair value)	$ 649,923	$ 665,571
General Obligation Bonds [Member] | Illinois [Member]
Number of issuers	19	9
Amortized cost	$ 30,063,690	$ 10,928,700
Other Investments	30,437,115	11,264,348
Average exposure per issuer (fair value)	$ 1,601,953	$ 1,251,594
General Obligation Bonds [Member] | North Dakota [Member]
Number of issuers	6	5
Amortized cost	$ 19,403,728	$ 10,890,000
Other Investments	19,906,421	11,050,235
Average exposure per issuer (fair value)	$ 3,317,737	$ 2,210,047
General Obligation Bonds [Member] | Other States [Member]
Number of issuers	49	41
Amortized cost	$ 23,934,196	$ 16,965,393
Other Investments	24,247,257	17,229,485
Average exposure per issuer (fair value)	$ 494,842	$ 420,231
General Obligation Bonds [Member]
Number of issuers	114	82
Amortized cost	$ 113,995,610	$ 66,683,832
Other Investments	115,786,252	67,778,032
Average exposure per issuer (fair value)	$ 1,015,669	$ 826,561
Revenue Bonds [Member] | Iowa [Member]
Number of issuers	30	26
Amortized cost	$ 75,440,709	$ 70,773,660
Other Investments	77,216,784	71,659,410
Average exposure per issuer (fair value)	$ 2,573,893	$ 2,756,131
Revenue Bonds [Member] | Missouri [Member]
Number of issuers	44	41
Amortized cost	$ 90,171,820	$ 78,593,590
Other Investments	91,084,628	79,015,378
Average exposure per issuer (fair value)	$ 2,070,105	$ 1,927,204
Revenue Bonds [Member] | North Dakota [Member]
Number of issuers	4
Amortized cost	$ 8,114,931
Other Investments	8,175,230
Average exposure per issuer (fair value)	$ 2,043,808
Revenue Bonds [Member] | Indiana [Member]
Number of issuers	20	17
Amortized cost	$ 43,994,737	$ 40,018,381
Other Investments	44,605,536	40,210,320
Average exposure per issuer (fair value)	$ 2,230,277	$ 2,365,313
Revenue Bonds [Member] | Kansas [Member]
Number of issuers	6	3
Amortized cost	$ 13,480,269	$ 11,748,679
Other Investments	13,587,744	11,821,055
Average exposure per issuer (fair value)	$ 2,264,624	$ 3,940,352
Revenue Bonds [Member] | Other States [Member]
Number of issuers	8	5
Amortized cost	$ 14,379,998	$ 11,570,998
Other Investments	14,628,631	11,735,678
Average exposure per issuer (fair value)	$ 1,828,579	$ 2,347,136
Revenue Bonds [Member]
Number of issuers	112	92
Amortized cost	$ 245,582,464	$ 212,705,308
Other Investments	249,298,553	214,441,841
Average exposure per issuer (fair value)	$ 2,225,880	$ 2,330,890