Note 2 - Securities - Securities With Unrealized Losses (Details) - USD ($) $ in Thousands	Sep. 30, 2017	Dec. 31, 2016
Securities available-for-sale, less than 12 months, fair value	$ 213,512	$ 300,218
Securities available-for-sale, less than 12 months, unrealized losses	402	3,597
Securities available-for-sale, 12 months or more, fair value	142,244	14,877
Securities available-for-sale, 12 months or more, unrealized losses	2,183	529
Securities available-for-sale, fair value	355,756	315,095
Securities available-for-sale, unrealized losses	2,585	4,126
US Government-sponsored Enterprises Debt Securities [Member]
Securities available-for-sale, less than 12 months, fair value	190,462	154,951
Securities available-for-sale, less than 12 months, unrealized losses	135	1,344
Securities available-for-sale, 12 months or more, fair value	70,176	3,485
Securities available-for-sale, 12 months or more, unrealized losses	643	150
Securities available-for-sale, fair value	260,638	158,436
Securities available-for-sale, unrealized losses	778	1,494
Mortgage-backed Securities, Issued by US Government Sponsored Enterprises [Member]
Securities available-for-sale, less than 12 months, fair value	13,227	115,374
Securities available-for-sale, less than 12 months, unrealized losses	117	1,873
Securities available-for-sale, 12 months or more, fair value	65,781	9,914
Securities available-for-sale, 12 months or more, unrealized losses	1,464	363
Securities available-for-sale, fair value	79,008	125,288
Securities available-for-sale, unrealized losses	1,581	2,236
US States and Political Subdivisions Debt Securities [Member]
Securities available-for-sale, less than 12 months, fair value	9,307	29,893
Securities available-for-sale, less than 12 months, unrealized losses	13	380
Securities available-for-sale, 12 months or more, fair value	6,287	1,478
Securities available-for-sale, 12 months or more, unrealized losses	76	16
Securities available-for-sale, fair value	15,594	31,371
Securities available-for-sale, unrealized losses	89	$ 396
Corporate Debt Securities [Member]
Securities available-for-sale, less than 12 months, fair value	516
Securities available-for-sale, less than 12 months, unrealized losses	137
Securities available-for-sale, 12 months or more, fair value
Securities available-for-sale, 12 months or more, unrealized losses
Securities available-for-sale, fair value	516
Securities available-for-sale, unrealized losses	$ 137