Note 9 - Securities Sold Under Agreements to Repurchase - Securities Sold Under Agreement to Repurchase (Details) - USD ($)	12 Months Ended
	Dec. 31, 2018	Dec. 31, 2017
Outstanding balance at year-end	$ 103,519,000	$ 118,748,000
Average daily balance during the year	101,005,000	116,587,000
Maximum daily balance during the year	$ 123,046,000	$ 142,459,000
Securities Sold under Agreements to Repurchase [Member]
Weighted average interest rate at year-end	0.26%	0.16%
Weighted average interest rate during the year	0.24%	0.16%