Note 2 - Securities - Securities With Unrealized Losses (Details) - USD ($) $ in Thousands	Mar. 31, 2017	Dec. 31, 2016
Less than 12 months, fair value	$ 227,964	$ 300,218
Less than 12 months, Unrealized losses	2,756	3,597
12 months or more, Fair value	24,855	14,877
12 months or more, Unrealized losses	555	529
Fair value	252,819	315,095
Unrealized losses	3,311	4,126
US Government-sponsored Enterprises Debt Securities [Member]
Less than 12 months, fair value	111,725	154,951
Less than 12 months, Unrealized losses	883	1,344
12 months or more, Fair value	12,887	3,485
12 months or more, Unrealized losses	193	150
Fair value	124,612	158,436
Unrealized losses	1,076	1,494
Mortgage-backed Securities, Issued by US Government Sponsored Enterprises [Member]
Less than 12 months, fair value	97,143	115,374
Less than 12 months, Unrealized losses	1,699	1,873
12 months or more, Fair value	9,431	9,914
12 months or more, Unrealized losses	338	363
Fair value	106,574	125,288
Unrealized losses	2,037	2,236
US States and Political Subdivisions Debt Securities [Member]
Less than 12 months, fair value	19,096	29,893
Less than 12 months, Unrealized losses	174	380
12 months or more, Fair value	2,537	1,478
12 months or more, Unrealized losses	24	16
Fair value	21,633	31,371
Unrealized losses	$ 198	$ 396