Note 8 - Securities Sold Under Agreements to Repurchase - Securities Sold Under Agreements to Repurchase (Details) - Securities Sold under Agreements to Repurchase [Member] - USD ($)	3 Months Ended
	Mar. 31, 2019	Mar. 31, 2018	Dec. 31, 2018
Outstanding balance at end of period	$ 34,633		$ 36,094
Weighted average interest rate at end of period	0.30%		0.24%
Average outstanding balance during the period	$ 37,528,000	$ 71,276,000
Average interest rate during the period	0.27%	0.19%
Maximum outstanding at any month end during the period	$ 38,445,000	$ 74,725,000