Note 2 - Securities - Securities in a Continuous Loss Position (Details) - USD ($)	Sep. 30, 2018	Dec. 31, 2017
Securities available for sale, continuous unrealized loss position, less than 12 months	$ 148,264,000	$ 60,173,000
Securities available for sale, continuous unrealized loss position, less than 12 months, unrealized loss	4,248,000	733,000
Securities available for sale, continuous unrealized loss position, 12 months or more	158,620,000	192,348,000
Securities available for sale, continuous unrealized loss position, 12 months or more, unrealized loss	13,117,000	6,826,000
Securities available for sale, continuous unrealized loss position	306,884,000	252,521,000
Securities available for sale, continuous unrealized loss position, unrealized loss	17,365,000	7,559,000
US Government Agencies Debt Securities [Member]
Securities available for sale, continuous unrealized loss position, less than 12 months	60,017,000	35,677,000
Securities available for sale, continuous unrealized loss position, less than 12 months, unrealized loss	2,623,000	434,000
Securities available for sale, continuous unrealized loss position, 12 months or more	120,797,000	115,374,000
Securities available for sale, continuous unrealized loss position, 12 months or more, unrealized loss	11,463,000	5,918,000
Securities available for sale, continuous unrealized loss position	180,814,000	151,051,000
Securities available for sale, continuous unrealized loss position, unrealized loss	14,086,000	6,352,000
Collateralized Mortgage Backed Securities [Member]
Securities available for sale, continuous unrealized loss position, less than 12 months	15,460,000	10,179,000
Securities available for sale, continuous unrealized loss position, less than 12 months, unrealized loss	484,000	156,000
Securities available for sale, continuous unrealized loss position, 12 months or more	22,444,000	21,084,000
Securities available for sale, continuous unrealized loss position, 12 months or more, unrealized loss	787,000	354,000
Securities available for sale, continuous unrealized loss position	37,904,000	31,263,000
Securities available for sale, continuous unrealized loss position, unrealized loss	1,271,000	510,000
Municipal General Obligation Bonds [Member]
Securities available for sale, continuous unrealized loss position, less than 12 months	70,463,000	12,807,000
Securities available for sale, continuous unrealized loss position, less than 12 months, unrealized loss	1,117,000	114,000
Securities available for sale, continuous unrealized loss position, 12 months or more	14,328,000	54,703,000
Securities available for sale, continuous unrealized loss position, 12 months or more, unrealized loss	804,000	524,000
Securities available for sale, continuous unrealized loss position	84,791,000	67,510,000
Securities available for sale, continuous unrealized loss position, unrealized loss	1,921,000	638,000
Municipal Revenue Bonds [Member]
Securities available for sale, continuous unrealized loss position, less than 12 months	2,324,000	0
Securities available for sale, continuous unrealized loss position, less than 12 months, unrealized loss	24,000	0
Securities available for sale, continuous unrealized loss position, 12 months or more	1,051,000	1,187,000
Securities available for sale, continuous unrealized loss position, 12 months or more, unrealized loss	63,000	30,000
Securities available for sale, continuous unrealized loss position	3,375,000	1,187,000
Securities available for sale, continuous unrealized loss position, unrealized loss	87,000	30,000
Other Debt and Equity Securities [Member]
Securities available for sale, continuous unrealized loss position, less than 12 months	0	1,510,000
Securities available for sale, continuous unrealized loss position, less than 12 months, unrealized loss	0	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	0	1,510,000
Securities available for sale, continuous unrealized loss position, unrealized loss	$ 0	$ 29,000