Note 6 - Investment Securities (Details) - Temporarily Impaired Securities - USD ($) $ in Thousands	Jun. 30, 2015	Dec. 31, 2014
Securities Available-for-Sale
Securities Available-for-Sale - Less than 12 Months - Fair Value	$ 1,087,454	$ 376,601
Securities Available-for-Sale - Less than 12 Months - Unrealized Losses	9,655	3,998
Securities Available-for-Sale - 12 Months or longer - Fair Value	49,812	494,754
Securities Available-for-Sale - 12 Months or longer - Unrealized Losses	1,265	7,801
Securities Available-for-Sale - Fair Value	1,137,266	871,355
Securities Available-for-Sale - Unrealized Losses	10,920	11,799
Collateralized Mortgage Backed Securities [Member]
Securities Available-for-Sale
Securities Available-for-Sale - Less than 12 Months - Fair Value	1,087,436
Securities Available-for-Sale - Less than 12 Months - Unrealized Losses	9,653
Securities Available-for-Sale - 12 Months or longer - Fair Value	6
Securities Available-for-Sale - 12 Months or longer - Unrealized Losses	1
Securities Available-for-Sale - Fair Value	1,087,442
Securities Available-for-Sale - Unrealized Losses	9,654
Collateralized Mortgage Obligations [Member]
Securities Available-for-Sale
Securities Available-for-Sale - 12 Months or longer - Fair Value	40	45
Securities Available-for-Sale - 12 Months or longer - Unrealized Losses	30	34
Securities Available-for-Sale - Fair Value	40	45
Securities Available-for-Sale - Unrealized Losses	30	34
Corporate Debt Securities [Member]
Securities Available-for-Sale
Securities Available-for-Sale - 12 Months or longer - Fair Value	43,922	63,753
Securities Available-for-Sale - 12 Months or longer - Unrealized Losses	1,078	1,247
Securities Available-for-Sale - Fair Value	43,922	63,753
Securities Available-for-Sale - Unrealized Losses	1,078	1,247
Mutual Funds [Member]
Securities Available-for-Sale
Securities Available-for-Sale - 12 Months or longer - Fair Value	5,844	5,866
Securities Available-for-Sale - 12 Months or longer - Unrealized Losses	156	134
Securities Available-for-Sale - Fair Value	5,844	5,866
Securities Available-for-Sale - Unrealized Losses	156	134
Other Equity Securities [Member]
Securities Available-for-Sale
Securities Available-for-Sale - Less than 12 Months - Fair Value	18
Securities Available-for-Sale - Less than 12 Months - Unrealized Losses	2
Securities Available-for-Sale - Fair Value	18
Securities Available-for-Sale - Unrealized Losses	$ 2
US Treasury Securities [Member]
Securities Available-for-Sale
Securities Available-for-Sale - Less than 12 Months - Fair Value		374,153
Securities Available-for-Sale - Less than 12 Months - Unrealized Losses		265
Securities Available-for-Sale - Fair Value		374,153
Securities Available-for-Sale - Unrealized Losses		265
Mortgage Backed Securities Non Agency [Member]
Securities Available-for-Sale
Securities Available-for-Sale - 12 Months or longer - Fair Value		425,090
Securities Available-for-Sale - 12 Months or longer - Unrealized Losses		6,386
Securities Available-for-Sale - Fair Value		425,090
Securities Available-for-Sale - Unrealized Losses		6,386
Preferred Stock of Government Sponsored Entities [Member]
Securities Available-for-Sale
Securities Available-for-Sale - Less than 12 Months - Fair Value		2,448
Securities Available-for-Sale - Less than 12 Months - Unrealized Losses		3,733
Securities Available-for-Sale - Fair Value		2,448
Securities Available-for-Sale - Unrealized Losses		$ 3,733

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