Note 6 - Securities Sold Under Agreements to Repurchase - Securities Sold Under Agreement to Repurchase (Details) - USD ($)	9 Months Ended	12 Months Ended
	Sep. 30, 2016	Dec. 31, 2015
Securities sold under agreements to repurchase	$ 146,843,000	$ 154,771,000
Average interest rate at end of period	0.16%	0.11%
Average daily balance during the period	$ 151,691,000	$ 146,826,000
Average interest rate during the period	0.13%	0.11%
Maximum daily balance during the period	$ 175,088,000	$ 168,211,000