Note 3 - Investment Securities (Details) - Securities with Unrealized Losses (USD $) In Thousands, unless otherwise specified	12 Months Ended
Dec. 31, 2014	Dec. 31, 2013
Held-to-Maturity
Held-to-Maturity Securities Less Than 12 Months Estimated Fair Value	$ 333,275	$ 420,984
Held-to-Maturity Securities Less Than 12 Months Gross Unrealized Losses	3,011	12,158
Held-to-Maturity Securities 12 Months or More Estimated Fair Value	107,624	118,805
Held-to-Maturity Securities 12 Months or More Gross Unrealized Losses	2,028	4,317
Held-to-Maturity Securities Estimated Fair Value	440,899	539,790
Held-to-Maturity Securities Gross Unrealized Losses	5,039	16,475
Available-for-Sale
Available-for-Sale Securities Less Than 12 Months Estimated Fair Value	178,417	119,141
Available-for-Sale Securities Less Than 12 Months Gross Unrealized Losses	1,499	2,702
Available-for-Sale Securities 12 Months or More Estimated Fair Value	61,195	56,396
Available-for-Sale Securities 12 Months or More Gross Unrealized Losses	1,108	2,890
Available-for-Sale Securities Estimated Fair Value	239,612	175,537
Available-for-Sale Securities Gross Unrealized Losses	2,607	5,592
US Government Agencies Debt Securities [Member]
Held-to-Maturity
Held-to-Maturity Securities Less Than 12 Months Estimated Fair Value	265,591	258,474
Held-to-Maturity Securities Less Than 12 Months Gross Unrealized Losses	2,500	6,405
Held-to-Maturity Securities 12 Months or More Estimated Fair Value	84,398	114,339
Held-to-Maturity Securities 12 Months or More Gross Unrealized Losses	1,555	4,130
Held-to-Maturity Securities Estimated Fair Value	349,989	372,814
Held-to-Maturity Securities Gross Unrealized Losses	4,055	10,535
Available-for-Sale
Available-for-Sale Securities Less Than 12 Months Estimated Fair Value	171,114	3,985
Available-for-Sale Securities Less Than 12 Months Gross Unrealized Losses	1,472	16
Available-for-Sale Securities 12 Months or More Estimated Fair Value	61,195
Available-for-Sale Securities 12 Months or More Gross Unrealized Losses	1,108
Available-for-Sale Securities Estimated Fair Value	232,309	3,985
Available-for-Sale Securities Gross Unrealized Losses	2,580	16
Collateralized Mortgage Backed Securities [Member]
Held-to-Maturity
Held-to-Maturity Securities Less Than 12 Months Estimated Fair Value	10,077	32,053
Held-to-Maturity Securities Less Than 12 Months Gross Unrealized Losses	67	442
Held-to-Maturity Securities 12 Months or More Estimated Fair Value	14,250
Held-to-Maturity Securities 12 Months or More Gross Unrealized Losses	344
Held-to-Maturity Securities Estimated Fair Value	24,327	32,053
Held-to-Maturity Securities Gross Unrealized Losses	411	442
Available-for-Sale
Available-for-Sale Securities Less Than 12 Months Estimated Fair Value	1,542	111,662
Available-for-Sale Securities Less Than 12 Months Gross Unrealized Losses	7	2,682
Available-for-Sale Securities 12 Months or More Estimated Fair Value		56,396
Available-for-Sale Securities 12 Months or More Gross Unrealized Losses		2,890
Available-for-Sale Securities Estimated Fair Value	1,542	168,058
Available-for-Sale Securities Gross Unrealized Losses	7	5,572
US States and Political Subdivisions Debt Securities [Member]
Held-to-Maturity
Held-to-Maturity Securities Less Than 12 Months Estimated Fair Value	57,607	130,457
Held-to-Maturity Securities Less Than 12 Months Gross Unrealized Losses	444	5,311
Held-to-Maturity Securities 12 Months or More Estimated Fair Value	8,976	4,466
Held-to-Maturity Securities 12 Months or More Gross Unrealized Losses	129	187
Held-to-Maturity Securities Estimated Fair Value	66,583	134,923
Held-to-Maturity Securities Gross Unrealized Losses	573	5,498
Available-for-Sale
Available-for-Sale Securities Less Than 12 Months Estimated Fair Value	1,005	2,921
Available-for-Sale Securities Less Than 12 Months Gross Unrealized Losses	3	3
Available-for-Sale Securities Estimated Fair Value	1,005	2,921
Available-for-Sale Securities Gross Unrealized Losses	3	3
US Treasury Securities [Member]
Available-for-Sale
Available-for-Sale Securities Less Than 12 Months Estimated Fair Value	3,992
Available-for-Sale Securities Less Than 12 Months Gross Unrealized Losses	9
Available-for-Sale Securities Estimated Fair Value	3,992
Available-for-Sale Securities Gross Unrealized Losses	9
Other Securities [Member]
Available-for-Sale
Available-for-Sale Securities Less Than 12 Months Estimated Fair Value	764	573
Available-for-Sale Securities Less Than 12 Months Gross Unrealized Losses	8	1
Available-for-Sale Securities Estimated Fair Value	764	573
Available-for-Sale Securities Gross Unrealized Losses	$ 8	$ 1

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Amount of unrealized loss on securities classified as available-for-sale that have been in a loss position for twelve months or longer.

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