Note 9 - Short-term Borrowings - Overnight Repurchase Agreements (Details) - USD ($)	12 Months Ended
	Dec. 31, 2016	Dec. 31, 2015
Repurchase Agreements with Customers [Member]
Average daily balance during the period	$ 30,082,866	$ 121,186,231
Average daily interest rate during the period	0.07%	0.11%
Maximum month-end balance during the period	$ 59,833,229	$ 159,407,193
Weighted average rate as of end of period	0.02%	0.11%
Federal Funds Purchased [Member]
Average daily balance during the period	$ 19,105,595	$ 32,826,489
Average daily interest rate during the period	0.56%	0.41%
Maximum month-end balance during the period	$ 51,750,000	$ 126,220,000
Weighted average rate as of end of period	0.70%	0.57%