Note 3 - Investment Securities (Details) - Investment Securities (USD $) In Thousands, unless otherwise specified	12 Months Ended
Dec. 31, 2014	Dec. 31, 2013
Note 3 - Investment Securities (Details) - Investment Securities [Line Items]
Held-to-Maturity Securities Amortized Cost	$ 777,587us-gaap_HeldToMaturitySecurities	$ 745,688us-gaap_HeldToMaturitySecurities
Held-to-Maturity Securities Gross Unrealized Gains	7,985	2,232
Held-to-Maturity Securities Gross Unrealized (Losses)	(5,039)	(16,475)
Held-to-Maturity Securities Estimated Fair Value	780,533	731,445
Available-for-Sale Securities Amortized Cost	307,481	217,217
Available-for-Sale Securities Gross Unrealized Gains	409	652
Available-for-Sale Securities Gross Unrealized (Losses)	(2,607)	(5,592)
Available-for-Sale Securities Estimated Fair Value	305,283us-gaap_AvailableForSaleSecurities	212,277us-gaap_AvailableForSaleSecurities
US Government Agencies Debt Securities [Member]
Note 3 - Investment Securities (Details) - Investment Securities [Line Items]
Held-to-Maturity Securities Amortized Cost	418,914	395,198
Held-to-Maturity Securities Gross Unrealized Gains	929	50
Held-to-Maturity Securities Gross Unrealized (Losses)	(4,055)	(10,535)
Held-to-Maturity Securities Estimated Fair Value	415,788	384,713
Available-for-Sale Securities Amortized Cost	275,381	183,781
Available-for-Sale Securities Gross Unrealized Gains	15	8
Available-for-Sale Securities Gross Unrealized (Losses)	(2,580)	(5,572)
Available-for-Sale Securities Estimated Fair Value	272,816	178,217
Mortgage-backed Securities, Issued by Private Enterprises [Member]
Note 3 - Investment Securities (Details) - Investment Securities [Line Items]
Held-to-Maturity Securities Amortized Cost	29,743	34,425
Held-to-Maturity Securities Gross Unrealized Gains	56	17
Held-to-Maturity Securities Gross Unrealized (Losses)	(411)	(442)
Held-to-Maturity Securities Estimated Fair Value	29,388	34,000
Available-for-Sale Securities Amortized Cost	1,579	1,735
Available-for-Sale Securities Gross Unrealized Gains		156
Available-for-Sale Securities Gross Unrealized (Losses)	(7)
Available-for-Sale Securities Estimated Fair Value	1,572	1,891
US States and Political Subdivisions Debt Securities [Member]
Note 3 - Investment Securities (Details) - Investment Securities [Line Items]
Held-to-Maturity Securities Amortized Cost	328,310	315,445
Held-to-Maturity Securities Gross Unrealized Gains	7,000	2,165
Held-to-Maturity Securities Gross Unrealized (Losses)	(573)	(5,498)
Held-to-Maturity Securities Estimated Fair Value	334,737	312,112
Available-for-Sale Securities Amortized Cost	6,536	7,860
Available-for-Sale Securities Gross Unrealized Gains	7	4
Available-for-Sale Securities Gross Unrealized (Losses)	(3)	(3)
Available-for-Sale Securities Estimated Fair Value	6,540	7,861
Other Securities [Member]
Note 3 - Investment Securities (Details) - Investment Securities [Line Items]
Held-to-Maturity Securities Amortized Cost	620	620
Held-to-Maturity Securities Estimated Fair Value	620	620
Available-for-Sale Securities Amortized Cost	19,985	19,840
Available-for-Sale Securities Gross Unrealized Gains	386	484
Available-for-Sale Securities Gross Unrealized (Losses)	(8)	(1)
Available-for-Sale Securities Estimated Fair Value	20,363	20,323
US Treasury Securities [Member]
Note 3 - Investment Securities (Details) - Investment Securities [Line Items]
Available-for-Sale Securities Amortized Cost	4,000	4,001
Available-for-Sale Securities Gross Unrealized Gains	1
Available-for-Sale Securities Gross Unrealized (Losses)	(9)	(16)
Available-for-Sale Securities Estimated Fair Value	$ 3,992	$ 3,985

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