Note 2 - Securities - Securities With Unrealized Losses (Details) - USD ($) $ in Thousands	Jun. 30, 2017	Dec. 31, 2016
Securities available-for-sale, 12 months or more, fair value	$ 50,624	$ 14,877
Securities available-for-sale, 12 months or more, unrealized losses	629	529
Securities available-for-sale, fair value	336,236	315,095
Securities available-for-sale, unrealized losses	2,743	4,126
Securities available-for-sale, less than 12 months, fair value	285,612	300,218
Securities available-for-sale, less than 12 months, unrealized losses	2,114	3,597
US Government-sponsored Enterprises Debt Securities [Member]
Securities available-for-sale, 12 months or more, fair value	37,819	3,485
Securities available-for-sale, 12 months or more, unrealized losses	210	150
Securities available-for-sale, fair value	223,322	158,436
Securities available-for-sale, unrealized losses	873	1,494
Securities available-for-sale, less than 12 months, fair value	185,503	154,951
Securities available-for-sale, less than 12 months, unrealized losses	663	1,344
Mortgage-backed Securities, Issued by US Government Sponsored Enterprises [Member]
Securities available-for-sale, 12 months or more, fair value	9,952	9,914
Securities available-for-sale, 12 months or more, unrealized losses	385	363
Securities available-for-sale, fair value	97,113	125,288
Securities available-for-sale, unrealized losses	1,768	2,236
Securities available-for-sale, less than 12 months, fair value	87,161	115,374
Securities available-for-sale, less than 12 months, unrealized losses	1,383	1,873
US States and Political Subdivisions Debt Securities [Member]
Securities available-for-sale, 12 months or more, fair value	2,853	1,478
Securities available-for-sale, 12 months or more, unrealized losses	34	16
Securities available-for-sale, fair value	15,801	31,371
Securities available-for-sale, unrealized losses	102	396
Securities available-for-sale, less than 12 months, fair value	12,948	29,893
Securities available-for-sale, less than 12 months, unrealized losses	$ 68	$ 380