Note 8 - Short-term Borrowings - Federal Funds Purchased and Short-term Borrowings (Details) - USD ($) $ in Thousands	6 Months Ended	12 Months Ended
	Jun. 30, 2018	Dec. 31, 2017
Balance at Period End, Amount	$ 47,179	$ 39,605
Federal Funds Purchased [Member]
Average Balance Outstanding During the Period, Amount	$ 75	$ 75
Average Balance Outstanding During the Period, Weighted Average Rate	2.69%
Maximum Amount Outstanding at any Month End, Amount	$ 1,500	$ 550
Other Short-term Debt [Member]
Average Balance Outstanding During the Period, Amount	$ 37,994	$ 215
Average Balance Outstanding During the Period, Weighted Average Rate	1.83%	0.93%
Maximum Amount Outstanding at any Month End, Amount	$ 98,960	$ 13,764
Balance at Period End, Amount	$ 17,978	$ 13,764
Balance at Period End, Weighted Average Rate	2.10%	1.57%
Securities Sold under Agreements to Repurchase [Member]
Average Balance Outstanding During the Period, Amount	$ 26,290	$ 26,350
Average Balance Outstanding During the Period, Weighted Average Rate	0.46%	0.31%
Maximum Amount Outstanding at any Month End, Amount	$ 35,661	$ 27,951
Balance at Period End, Amount	$ 29,201	$ 25,841
Balance at Period End, Weighted Average Rate	0.52%	0.26%
Carrying Value, Amount	$ 98,346	$ 38,953
Market Value, Amount	$ 96,906	$ 38,081