Note 6 - Investment Securities (Details) - Temporarily Impaired Securities - USD ($) $ in Thousands	Mar. 31, 2016	Dec. 31, 2015
Securities Available-for-Sale
Securities Available-for-Sale - Less than 12 Months - Fair Value	$ 42,534	$ 1,410,387
Securities Available-for-Sale - Less than 12 Months - Unrealized Losses	546	14,253
Securities Available-for-Sale - 12 Months or longer - Fair value	48,778	49,400
Securities Available-for-Sale - 12 Months or longer - Unrealized Losses	2,329	1,670
Securities Available-for-Sale - Fair Value	91,312	1,459,787
Securities Available-for-Sale - Unrealized Losses	2,875	15,923
US Treasury Securities [Member]
Securities Available-for-Sale
Securities Available-for-Sale - Less than 12 Months - Fair Value	29,965	224,289
Securities Available-for-Sale - Less than 12 Months - Unrealized Losses	7	395
Securities Available-for-Sale - Fair Value	29,965	224,289
Securities Available-for-Sale - Unrealized Losses	7	395
Collateralized Mortgage Backed Securities [Member]
Securities Available-for-Sale
Securities Available-for-Sale - Less than 12 Months - Fair Value	389	1,025,342
Securities Available-for-Sale - Less than 12 Months - Unrealized Losses	3	11,398
Securities Available-for-Sale - 12 Months or longer - Fair value	46	6
Securities Available-for-Sale - 12 Months or longer - Unrealized Losses	1	1
Securities Available-for-Sale - Fair Value	435	1,025,348
Securities Available-for-Sale - Unrealized Losses	4	11,399
Collateralized Mortgage Obligations [Member]
Securities Available-for-Sale
Securities Available-for-Sale - 12 Months or longer - Fair value	34	36
Securities Available-for-Sale - 12 Months or longer - Unrealized Losses	26	27
Securities Available-for-Sale - Fair Value	34	36
Securities Available-for-Sale - Unrealized Losses	26	27
Corporate Debt Securities [Member]
Securities Available-for-Sale
Securities Available-for-Sale - Less than 12 Months - Fair Value	9,950	9,950
Securities Available-for-Sale - Less than 12 Months - Unrealized Losses	50	50
Securities Available-for-Sale - 12 Months or longer - Fair value	42,783	43,525
Securities Available-for-Sale - 12 Months or longer - Unrealized Losses	2,217	1,475
Securities Available-for-Sale - Fair Value	52,733	53,475
Securities Available-for-Sale - Unrealized Losses	2,267	1,525
Mutual Funds [Member]
Securities Available-for-Sale
Securities Available-for-Sale - 12 Months or longer - Fair value	5,915	5,833
Securities Available-for-Sale - 12 Months or longer - Unrealized Losses	85	167
Securities Available-for-Sale - Fair Value	5,915	5,833
Securities Available-for-Sale - Unrealized Losses	85	167
Preferred Stock of Government Sponsored Entities [Member]
Securities Available-for-Sale
Securities Available-for-Sale - Less than 12 Months - Fair Value	2,230	2,488
Securities Available-for-Sale - Less than 12 Months - Unrealized Losses	486	228
Securities Available-for-Sale - Fair Value	2,230	2,488
Securities Available-for-Sale - Unrealized Losses	$ 486	228
US Government-sponsored Enterprises Debt Securities [Member]
Securities Available-for-Sale
Securities Available-for-Sale - Less than 12 Months - Fair Value		148,160
Securities Available-for-Sale - Less than 12 Months - Unrealized Losses		1,840
Securities Available-for-Sale - Fair Value		148,160
Securities Available-for-Sale - Unrealized Losses		1,840
Other Equity Securities [Member]
Securities Available-for-Sale
Securities Available-for-Sale - Less than 12 Months - Fair Value		158
Securities Available-for-Sale - Less than 12 Months - Unrealized Losses		342
Securities Available-for-Sale - Fair Value		158
Securities Available-for-Sale - Unrealized Losses		$ 342

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