Note 4 - Securities - Securities With Unrealized Losses (Details) - USD ($) $ in Thousands	Dec. 31, 2016	Dec. 31, 2015
Less than 12 months, fair value	$ 300,218	$ 165,097
Less than 12 months, Unrealized losses	3,597	1,193
12 months or more, Fair value	14,877	40,360
12 months or more, Unrealized losses	529	1,276
Fair value	315,095	205,457
Unrealized losses	4,126	2,469
US Government-sponsored Enterprises Debt Securities [Member]
Less than 12 months, fair value	154,951	102,098
Less than 12 months, Unrealized losses	1,344	500
12 months or more, Fair value	3,485	8,469
12 months or more, Unrealized losses	150	265
Fair value	158,436	110,567
Unrealized losses	1,494	765
Mortgage-backed Securities, Issued by US Government Sponsored Enterprises [Member]
Less than 12 months, fair value	115,374	49,774
Less than 12 months, Unrealized losses	1,873	662
12 months or more, Fair value	9,914	29,936
12 months or more, Unrealized losses	363	992
Fair value	125,288	79,710
Unrealized losses	2,236	1,654
US States and Political Subdivisions Debt Securities [Member]
Less than 12 months, fair value	29,893	13,225
Less than 12 months, Unrealized losses	380	31
12 months or more, Fair value	1,478	1,955
12 months or more, Unrealized losses	16	19
Fair value	31,371	15,180
Unrealized losses	$ 396	$ 50