Note 2 - Securities - Securities in a Continuous Loss Position (Details) - USD ($)	Sep. 30, 2017	Dec. 31, 2016
Securities available for sale, continuous unrealized loss position, less than 12 months	$ 115,245,000	$ 183,125,000
Securities available for sale, continuous unrealized loss position, less than 12 months, unrealized loss	2,726,000	8,655,000
Securities available for sale, continuous unrealized loss position, 12 months or more	66,218,000	70,085,000
Securities available for sale, continuous unrealized loss position, 12 months or more, unrealized loss	2,357,000	774,000
Securities available for sale, continuous unrealized loss position	181,463,000	253,210,000
Securities available for sale, continuous unrealized loss position, unrealized loss	5,083,000	9,429,000
US Government Agencies Debt Securities [Member]
Securities available for sale, continuous unrealized loss position, less than 12 months	81,981,000	110,160,000
Securities available for sale, continuous unrealized loss position, less than 12 months, unrealized loss	2,496,000	7,172,000
Securities available for sale, continuous unrealized loss position, 12 months or more	47,265,000	5,073,000
Securities available for sale, continuous unrealized loss position, 12 months or more, unrealized loss	2,095,000	165,000
Securities available for sale, continuous unrealized loss position	129,246,000	115,233,000
Securities available for sale, continuous unrealized loss position, unrealized loss	4,591,000	7,337,000
Collateralized Mortgage Backed Securities [Member]
Securities available for sale, continuous unrealized loss position, less than 12 months	21,482,000	3,670,000
Securities available for sale, continuous unrealized loss position, less than 12 months, unrealized loss	121,000	4,000
Securities available for sale, continuous unrealized loss position, 12 months or more	9,416,000	37,072,000
Securities available for sale, continuous unrealized loss position, 12 months or more, unrealized loss	93,000	419,000
Securities available for sale, continuous unrealized loss position	30,898,000	40,742,000
Securities available for sale, continuous unrealized loss position, unrealized loss	214,000	423,000
Municipal General Obligation Bonds [Member]
Securities available for sale, continuous unrealized loss position, less than 12 months	10,280,000	65,895,000
Securities available for sale, continuous unrealized loss position, less than 12 months, unrealized loss	90,000	1,360,000
Securities available for sale, continuous unrealized loss position, 12 months or more	8,436,000	27,734,000
Securities available for sale, continuous unrealized loss position, 12 months or more, unrealized loss	153,000	189,000
Securities available for sale, continuous unrealized loss position	18,716,000	93,629,000
Securities available for sale, continuous unrealized loss position, unrealized loss	243,000	1,549,000
Municipal Revenue Bonds [Member]
Securities available for sale, continuous unrealized loss position, less than 12 months	0	1,921,000
Securities available for sale, continuous unrealized loss position, less than 12 months, unrealized loss	0	90,000
Securities available for sale, continuous unrealized loss position, 12 months or more	1,101,000	206,000
Securities available for sale, continuous unrealized loss position, 12 months or more, unrealized loss	16,000	1,000
Securities available for sale, continuous unrealized loss position	1,101,000	2,127,000
Securities available for sale, continuous unrealized loss position, unrealized loss	16,000	91,000
Other Debt and Equity Securities [Member]
Securities available for sale, continuous unrealized loss position, less than 12 months	1,502,000	1,479,000
Securities available for sale, continuous unrealized loss position, less than 12 months, unrealized loss	19,000	29,000
Securities available for sale, continuous unrealized loss position, 12 months or more	0	0
Securities available for sale, continuous unrealized loss position, 12 months or more, unrealized loss	0	0
Securities available for sale, continuous unrealized loss position	1,502,000	1,479,000
Securities available for sale, continuous unrealized loss position, unrealized loss	$ 19,000	$ 29,000