Note 6 - Securities Sold Under Agreements to Repurchase (Details) - Securities Sold Under Agreement to Repurchase - USD ($)	3 Months Ended	12 Months Ended
	Mar. 31, 2016	Dec. 31, 2015
Securities Sold Under Agreement to Repurchase [Abstract]
Outstanding balance at end of period	$ 162,312,000	$ 154,771,000
Average interest rate at end of period	0.11%	0.11%
Average daily balance during the period	$ 158,281,000	$ 146,826,000
Average interest rate during the period	0.11%	0.11%
Maximum daily balance during the period	$ 175,088,000	$ 168,211,000