Note 3 - Securities - Securities in an Unrealized Loss Position (Details) - USD ($) $ in Thousands	Mar. 31, 2018	Dec. 31, 2017
Available-for-sale securities, less than 12 months, fair value	$ 135,085	$ 121,822
Available-for-sale securities, less than 12 months, unrealized losses	(3,517)	(1,363)
Available-for-sale securities, 12 months or more, fair value	51,429	54,495
Available-for-sale securities, 12 months or more, unrealized losses	(2,075)	(1,310)
Available-for-sale securities, fair value	186,514	176,317
Available-for-sale securities, unrealized losses	(5,592)	(2,673)
US Government Agencies Debt Securities [Member]
Available-for-sale securities, less than 12 months, fair value	15,195	18,140
Available-for-sale securities, less than 12 months, unrealized losses	(286)	(102)
Available-for-sale securities, 12 months or more, fair value	2,003	2,131
Available-for-sale securities, 12 months or more, unrealized losses	(66)	(44)
Available-for-sale securities, fair value	17,198	20,271
Available-for-sale securities, unrealized losses	(352)	(146)
US States and Political Subdivisions Debt Securities [Member]
Available-for-sale securities, less than 12 months, fair value	17,412	15,030
Available-for-sale securities, less than 12 months, unrealized losses	(534)	(255)
Available-for-sale securities, 12 months or more, fair value	5,809	8,368
Available-for-sale securities, 12 months or more, unrealized losses	(277)	(223)
Available-for-sale securities, fair value	23,221	23,398
Available-for-sale securities, unrealized losses	(811)	(478)
Residential Mortgage Backed Securities and Collateralized Mortgage Obligations [Member]
Available-for-sale securities, less than 12 months, fair value	88,513	75,323
Available-for-sale securities, less than 12 months, unrealized losses	(2,288)	(827)
Available-for-sale securities, 12 months or more, fair value	31,013	31,036
Available-for-sale securities, 12 months or more, unrealized losses	(1,274)	(711)
Available-for-sale securities, fair value	119,526	106,359
Available-for-sale securities, unrealized losses	(3,562)	(1,538)
Corporate Debt Securities [Member]
Available-for-sale securities, less than 12 months, fair value
Available-for-sale securities, less than 12 months, unrealized losses
Available-for-sale securities, 12 months or more, fair value	2,920	2,934
Available-for-sale securities, 12 months or more, unrealized losses	(114)	(105)
Available-for-sale securities, fair value	2,920	2,934
Available-for-sale securities, unrealized losses	(114)	(105)
Commercial Mortgage Backed Securities [Member]
Available-for-sale securities, less than 12 months, fair value	13,965	11,162
Available-for-sale securities, less than 12 months, unrealized losses	(409)	(151)
Available-for-sale securities, 12 months or more, fair value	9,684	10,026
Available-for-sale securities, 12 months or more, unrealized losses	(344)	(227)
Available-for-sale securities, fair value	23,649	21,188
Available-for-sale securities, unrealized losses	$ (753)	(378)
Asset-backed Securities [Member]
Available-for-sale securities, less than 12 months, fair value		2,167
Available-for-sale securities, less than 12 months, unrealized losses		(28)
Available-for-sale securities, 12 months or more, fair value
Available-for-sale securities, 12 months or more, unrealized losses
Available-for-sale securities, fair value		2,167
Available-for-sale securities, unrealized losses		$ (28)