Note 2 - Investment Securities - Amortized Cost and Fair Values of General Obligation Bonds and Revenue Bonds by Issuer's State (Details)	Mar. 31, 2017 USD ($)	Dec. 31, 2016 USD ($)
General Obligation Bonds [Member]
Number of issuers	112	116
Amortized cost	$ 99,815,329	$ 117,205,307
Other Investments	99,318,523	116,472,635
Average exposure per issuer (fair value)	$ 886,773	$ 1,004,074
General Obligation Bonds [Member] | Iowa [Member]
Number of issuers	27	27
Amortized cost	$ 32,227,250	$ 32,258,612
Other Investments	32,252,723	32,231,936
Average exposure per issuer (fair value)	$ 1,194,545	$ 1,193,775
General Obligation Bonds [Member] | Missouri [Member]
Number of issuers	15	14
Amortized cost	$ 8,060,239	$ 8,291,192
Other Investments	8,097,352	8,323,245
Average exposure per issuer (fair value)	$ 539,823	$ 594,518
General Obligation Bonds [Member] | North Dakota [Member]
Number of issuers	7	7
Amortized cost	$ 22,169,480	$ 22,169,050
Other Investments	21,572,627	21,499,075
Average exposure per issuer (fair value)	$ 3,081,804	$ 3,071,296
General Obligation Bonds [Member] | Illinois [Member]
Number of issuers	17	19
Amortized cost	$ 12,915,605	$ 29,214,559
Other Investments	13,060,349	29,308,438
Average exposure per issuer (fair value)	$ 768,256	$ 1,542,549
General Obligation Bonds [Member] | Ohio [Member]
Number of issuers	8	8
Amortized cost	$ 6,785,433	$ 6,790,398
Other Investments	6,635,402	6,651,897
Average exposure per issuer (fair value)	$ 829,425	$ 831,487
General Obligation Bonds [Member] | Other States [Member]
Number of issuers	38	41
Amortized cost	$ 17,657,322	$ 18,481,496
Other Investments	17,700,070	18,458,044
Average exposure per issuer (fair value)	$ 465,791	$ 450,196
Revenue Bonds [Member]
Number of issuers	123	120
Amortized cost	$ 256,933,052	$ 257,470,290
Other Investments	254,960,357	255,496,690
Average exposure per issuer (fair value)	$ 2,072,848	$ 2,129,139
Revenue Bonds [Member] | Iowa [Member]
Number of issuers	31	31
Amortized cost	$ 70,400,232	$ 70,788,393
Other Investments	70,771,347	71,142,393
Average exposure per issuer (fair value)	$ 2,282,947	$ 2,294,916
Revenue Bonds [Member] | Missouri [Member]
Number of issuers	50	47
Amortized cost	$ 92,894,184	$ 90,784,441
Other Investments	91,892,614	89,664,013
Average exposure per issuer (fair value)	$ 1,837,852	$ 1,907,745
Revenue Bonds [Member] | North Dakota [Member]
Number of issuers	4	4
Amortized cost	$ 7,992,074	$ 8,089,067
Other Investments	7,722,774	7,796,381
Average exposure per issuer (fair value)	$ 1,930,694	$ 1,949,095
Revenue Bonds [Member] | Indiana [Member]
Number of issuers	22	22
Amortized cost	$ 46,469,290	$ 47,994,737
Other Investments	45,838,852	47,582,138
Average exposure per issuer (fair value)	$ 2,083,584	$ 2,162,824
Revenue Bonds [Member] | Ohio [Member]
Number of issuers	3	3
Amortized cost	$ 13,650,000	$ 13,650,000
Other Investments	13,380,921	13,405,222
Average exposure per issuer (fair value)	$ 4,460,307	$ 4,468,407
Revenue Bonds [Member] | Kansas [Member]
Number of issuers	6	6
Amortized cost	$ 13,260,612	$ 13,476,366
Other Investments	13,243,053	13,427,491
Average exposure per issuer (fair value)	$ 2,207,176	$ 2,237,915
Revenue Bonds [Member] | Other States [Member]
Number of issuers	7	7
Amortized cost	$ 12,266,660	$ 12,687,286
Other Investments	12,110,796	12,479,052
Average exposure per issuer (fair value)	$ 1,730,114	$ 1,782,722