Note 2 - Amortized Cost and Fair Values of General Obligation Bonds by Issuer's State (Details)	Jun. 30, 2016 USD ($)	Dec. 31, 2015 USD ($)
General Obligation Bonds [Member] | Iowa [Member]
Number of issuers	13	15
Amortized cost	$ 19,441,057	$ 19,974,939
Fair value	19,965,926	20,247,108
Average exposure per issuer (fair value)	$ 1,535,840	$ 1,349,807
General Obligation Bonds [Member] | Missouri [Member]
Number of issuers	12	12
Amortized cost	$ 7,349,505	$ 7,924,800
Fair value	7,519,474	7,986,856
Average exposure per issuer (fair value)	$ 626,623	$ 665,571
General Obligation Bonds [Member] | Illinois [Member]
Number of issuers	9	9
Amortized cost	$ 10,127,747	$ 10,928,700
Fair value	10,527,337	11,264,348
Average exposure per issuer (fair value)	$ 1,169,704	$ 1,251,594
General Obligation Bonds [Member] | North Dakota [Member]
Number of issuers	6	5
Amortized cost	$ 16,208,320	$ 10,890,000
Fair value	16,872,189	11,050,235
Average exposure per issuer (fair value)	$ 2,812,032	$ 2,210,047
General Obligation Bonds [Member] | Other States [Member]
Number of issuers	37	41
Amortized cost	$ 13,738,908	$ 16,965,393
Fair value	14,133,036	17,229,485
Average exposure per issuer (fair value)	$ 381,974	$ 420,231
General Obligation Bonds [Member]
Number of issuers	77	82
Amortized cost	$ 66,865,537	$ 66,683,832
Fair value	69,017,962	67,778,032
Average exposure per issuer (fair value)	$ 896,337	$ 826,561
Revenue Bonds [Member] | Iowa [Member]
Number of issuers	26	26
Amortized cost	$ 73,076,794	$ 70,773,660
Fair value	74,933,480	71,659,410
Average exposure per issuer (fair value)	$ 2,882,057	$ 2,756,131
Revenue Bonds [Member] | Missouri [Member]
Number of issuers	41	41
Amortized cost	$ 89,033,470	$ 78,593,590
Fair value	90,174,695	79,015,378
Average exposure per issuer (fair value)	$ 2,199,383	$ 1,927,204
Revenue Bonds [Member] | North Dakota [Member]
Number of issuers	4
Amortized cost	$ 8,161,630
Fair value	8,359,661
Average exposure per issuer (fair value)	$ 2,089,915
Revenue Bonds [Member] | Indiana [Member]
Number of issuers	18	17
Amortized cost	$ 40,009,789	$ 40,018,381
Fair value	40,615,477	40,210,320
Average exposure per issuer (fair value)	$ 2,256,415	$ 2,365,313
Revenue Bonds [Member] | Kansas [Member]
Number of issuers	5	3
Amortized cost	$ 13,172,824	$ 11,748,679
Fair value	13,315,662	11,821,055
Average exposure per issuer (fair value)	$ 2,663,132	$ 3,940,352
Revenue Bonds [Member] | Other States [Member]
Number of issuers	5	5
Amortized cost	$ 11,438,676	$ 11,570,998
Fair value	11,734,995	11,735,678
Average exposure per issuer (fair value)	$ 2,346,999	$ 2,347,136
Revenue Bonds [Member]
Number of issuers	99	92
Amortized cost	$ 234,893,183	$ 212,705,308
Fair value	239,133,970	214,441,841
Average exposure per issuer (fair value)	$ 2,415,495	$ 2,330,890