Note 3 - Securities - Securities in an Unrealized Loss Position (Details) - USD ($) $ in Thousands	Sep. 30, 2018	Dec. 31, 2017
Available-for-sale securities, less than 12 months, fair value	$ 75,388	$ 121,822
Available-for-sale securities, less than 12 months, unrealized losses	(1,891)	(1,363)
Available-for-sale securities, 12 months or more, fair value	115,024	54,495
Available-for-sale securities, 12 months or more, unrealized losses	(5,035)	(1,311)
Available-for-sale securities, fair value	190,412	176,317
Available-for-sale securities, unrealized losses	(6,926)	(2,674)
US Government Agencies Debt Securities [Member]
Available-for-sale securities, less than 12 months, fair value	16,501	18,140
Available-for-sale securities, less than 12 months, unrealized losses	(225)	(102)
Available-for-sale securities, 12 months or more, fair value	9,060	2,131
Available-for-sale securities, 12 months or more, unrealized losses	(287)	(44)
Available-for-sale securities, fair value	25,561	20,271
Available-for-sale securities, unrealized losses	(512)	(146)
US States and Political Subdivisions Debt Securities [Member]
Available-for-sale securities, less than 12 months, fair value	10,394	15,030
Available-for-sale securities, less than 12 months, unrealized losses	(257)	(255)
Available-for-sale securities, 12 months or more, fair value	13,126	8,368
Available-for-sale securities, 12 months or more, unrealized losses	(652)	(223)
Available-for-sale securities, fair value	23,520	23,398
Available-for-sale securities, unrealized losses	(909)	(478)
Residential Mortgage Backed Securities and Collateralized Mortgage Obligations [Member]
Available-for-sale securities, less than 12 months, fair value	43,278	75,323
Available-for-sale securities, less than 12 months, unrealized losses	(1,250)	(827)
Available-for-sale securities, 12 months or more, fair value	72,572	31,036
Available-for-sale securities, 12 months or more, unrealized losses	(3,350)	(712)
Available-for-sale securities, fair value	115,850	106,359
Available-for-sale securities, unrealized losses	(4,600)	(1,539)
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	2,953	2,934
Available-for-sale securities, 12 months or more, unrealized losses	(73)	(105)
Available-for-sale securities, fair value	2,953	2,934
Available-for-sale securities, unrealized losses	(73)	(105)
Commercial Mortgage Backed Securities [Member]
Available-for-sale securities, less than 12 months, fair value	5,215	11,162
Available-for-sale securities, less than 12 months, unrealized losses	(159)	(151)
Available-for-sale securities, 12 months or more, fair value	17,313	10,026
Available-for-sale securities, 12 months or more, unrealized losses	(673)	(227)
Available-for-sale securities, fair value	22,528	21,188
Available-for-sale securities, unrealized losses	$ (832)	(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)