Note 3 - Available-for-sale Securities - Scheduled Maturities (Details) - USD ($)	Dec. 31, 2017	Dec. 31, 2016
Due in one year or less, amortized cost	$ 1,254,321	$ 121,744
Due in one year or less, fair value	1,256,906	121,884
Due after one to five years, amortized cost	21,574,631	29,365,434
Due after one to five years, fair value	21,306,086	28,889,086
Due after five to ten years, amortized cost	1,878,905	2,463,836
Due after five to ten years, fair value	1,836,889	2,488,162
Total, amortized cost	24,707,857	31,951,014
Total, fair value	$ 24,399,881	$ 31,499,132