Note 6 - Short-term Borrowings - Federal Funds Purchased and Short-term Borrowings (Details) - USD ($) $ in Thousands	9 Months Ended	12 Months Ended
	Sep. 30, 2017	Dec. 31, 2016
Balance at Period End, Amount	$ 24,662	$ 27,027
Federal Funds Purchased [Member]
Average Balance Outstanding During the Period, Amount	$ 11	$ 307
Average Balance Outstanding During the Period, Weighted Average Rate		0.65%
Maximum Amount Outstanding at any Month End, Amount	$ 550	$ 6,000
Other Short-term Debt [Member]
Average Balance Outstanding During the Period, Amount		$ 596
Average Balance Outstanding During the Period, Weighted Average Rate		0.67%
Maximum Amount Outstanding at any Month End, Amount		$ 6,160
Balance at Period End, Amount
Balance at Period End, Weighted Average Rate
Securities Sold under Agreements to Repurchase [Member]
Average Balance Outstanding During the Period, Amount	$ 26,302	$ 26,311
Average Balance Outstanding During the Period, Weighted Average Rate	0.30%	0.26%
Maximum Amount Outstanding at any Month End, Amount	$ 27,817	$ 30,095
Balance at Period End, Amount	$ 24,662	$ 27,027
Balance at Period End, Weighted Average Rate	0.25%	0.24%
Carrying Value, Amount	$ 35,128	$ 33,785
Market Value, Amount	$ 34,510	$ 32,931