Note 4 - Securities - Securities in an Unrealized Loss Position (Details) - USD ($) $ in Thousands	Dec. 31, 2017	Dec. 31, 2016
Available-for-sale securities, less than 12 months, fair value	$ 121,822	$ 105,042
Available-for-sale securities, less than 12 months, unrealized losses	(1,363)	(2,258)
Available-for-sale securities, 12 months or more, fair value	54,495	8,303
Available-for-sale securities, 12 months or more, unrealized losses	(1,310)	(250)
Available-for-sale securities, fair value	176,317	113,345
Available-for-sale securities, unrealized losses	(2,673)	(2,508)
US Government Agencies Debt Securities [Member]
Available-for-sale securities, less than 12 months, fair value	18,140	9,139
Available-for-sale securities, less than 12 months, unrealized losses	(102)	(83)
Available-for-sale securities, 12 months or more, fair value	2,131
Available-for-sale securities, 12 months or more, unrealized losses	(44)
Available-for-sale securities, fair value	20,271	9,139
Available-for-sale securities, unrealized losses	(146)	(83)
US States and Political Subdivisions Debt Securities [Member]
Available-for-sale securities, less than 12 months, fair value	15,030	20,329
Available-for-sale securities, less than 12 months, unrealized losses	(255)	(420)
Available-for-sale securities, 12 months or more, fair value	8,368
Available-for-sale securities, 12 months or more, unrealized losses	(223)
Available-for-sale securities, fair value	23,398	20,329
Available-for-sale securities, unrealized losses	(478)	(420)
Held-to-maturity securities, less than 12 months, fair value		11,639
Held-to-maturity securities, less than 12 months, unrealized losses		(425)
Held-to-maturity securities, 12 months or more, fair value		933
Held-to-maturity securities, 12 months or more, unrealized losses		(98)
Held-to-maturity securities, fair value		12,572
Held-to-maturity securities, unrealized losses		(523)
Residential Mortgage Backed Securities and Collateralized Mortgage Obligations [Member]
Available-for-sale securities, less than 12 months, fair value	75,323	52,345
Available-for-sale securities, less than 12 months, unrealized losses	(827)	(1,396)
Available-for-sale securities, 12 months or more, fair value	31,036	4,108
Available-for-sale securities, 12 months or more, unrealized losses	(711)	(101)
Available-for-sale securities, fair value	106,359	56,453
Available-for-sale securities, unrealized losses	(1,538)	(1,497)
Corporate Debt Securities [Member]
Available-for-sale securities, less than 12 months, fair value		8,908
Available-for-sale securities, less than 12 months, unrealized losses		(140)
Available-for-sale securities, 12 months or more, fair value	2,934
Available-for-sale securities, 12 months or more, unrealized losses	(105)
Available-for-sale securities, fair value	2,934	8,908
Available-for-sale securities, unrealized losses	(105)	(140)
Commercial Mortgage Backed Securities [Member]
Available-for-sale securities, less than 12 months, fair value	11,162	12,041
Available-for-sale securities, less than 12 months, unrealized losses	(151)	(191)
Available-for-sale securities, 12 months or more, fair value	10,026	2,849
Available-for-sale securities, 12 months or more, unrealized losses	(227)	(90)
Available-for-sale securities, fair value	21,188	14,890
Available-for-sale securities, unrealized losses	(378)	(281)
Asset-backed Securities [Member]
Available-for-sale securities, less than 12 months, fair value	2,167	2,280
Available-for-sale securities, less than 12 months, unrealized losses	(28)	(28)
Available-for-sale securities, 12 months or more, fair value		1,346
Available-for-sale securities, 12 months or more, unrealized losses		(59)
Available-for-sale securities, fair value	2,167	3,626
Available-for-sale securities, unrealized losses	$ (28)	$ (87)