Note 6 - Securities Sold Under Agreements to Repurchase - Securities Sold Under Agreement to Repurchase (Details) - USD ($)	6 Months Ended	12 Months Ended
	Jun. 30, 2017	Dec. 31, 2016
Securities sold under agreements to repurchase	$ 110,920,000	$ 131,710,000
Average interest rate at end of period	0.17%	0.16%
Average daily balance during the period	$ 121,823,000	$ 149,079,000
Average interest rate during the period	0.16%	0.14%
Maximum daily balance during the period	$ 142,459,000	$ 175,088,000