Note 9 - Short-term Borrowings - Overnight Repurchase Agreements (Details) - USD ($)	12 Months Ended
	Dec. 31, 2018	Dec. 31, 2017
Repurchase Agreements with Customers [Member]
Average daily balance during the period	$ 7,830,860	$ 7,475,824
Average daily interest rate during the period	0.38%	0.08%
Maximum month-end balance during the period	$ 10,391,529	$ 11,829,201
Weighted average rate as of end of period	0.90%	0.15%
Federal Funds Purchased [Member]
Average daily balance during the period	$ 13,059,102	$ 13,486,239
Average daily interest rate during the period	2.18%	1.31%
Maximum month-end balance during the period	$ 32,330,000	$ 33,650,000
Weighted average rate as of end of period	2.46%	1.24%