Note 7 - Investment Securities (Details) - Temporarily Impaired Securities - USD ($) $ in Thousands	Sep. 30, 2015	Dec. 31, 2014
Securities Available-for-Sale
Securities Available-for-Sale - Less than 12 Months - Fair Value	$ 713,835	$ 376,601
Securities Available-for-Sale - Less than 12 Months - Unrealized Losses	2,569	3,998
Securities Available-for-Sale - 12 Months or longer - Fair Value	49,502	494,754
Securities Available-for-Sale - 12 Months or longer - Unrealized Losses	1,573	7,801
Securities Available-for-Sale - Fair Value	763,337	871,355
Securities Available-for-Sale - Unrealized Losses	4,142	11,799
Collateralized Mortgage Backed Securities [Member]
Securities Available-for-Sale
Securities Available-for-Sale - Less than 12 Months - Fair Value	703,710
Securities Available-for-Sale - Less than 12 Months - Unrealized Losses	2,194
Securities Available-for-Sale - 12 Months or longer - Fair Value	7	425,090
Securities Available-for-Sale - 12 Months or longer - Unrealized Losses	1	6,386
Securities Available-for-Sale - Fair Value	703,717	425,090
Securities Available-for-Sale - Unrealized Losses	2,195	6,386
Collateralized Mortgage Obligations [Member]
Securities Available-for-Sale
Securities Available-for-Sale - 12 Months or longer - Fair Value	38	45
Securities Available-for-Sale - 12 Months or longer - Unrealized Losses	29	34
Securities Available-for-Sale - Fair Value	38	45
Securities Available-for-Sale - Unrealized Losses	29	34
Corporate Debt Securities [Member]
Securities Available-for-Sale
Securities Available-for-Sale - Less than 12 Months - Fair Value	9,950
Securities Available-for-Sale - Less than 12 Months - Unrealized Losses	50
Securities Available-for-Sale - 12 Months or longer - Fair Value	43,558	63,753
Securities Available-for-Sale - 12 Months or longer - Unrealized Losses	1,442	1,247
Securities Available-for-Sale - Fair Value	53,508	63,753
Securities Available-for-Sale - Unrealized Losses	1,492	1,247
Mutual Funds [Member]
Securities Available-for-Sale
Securities Available-for-Sale - 12 Months or longer - Fair Value	5,899	5,866
Securities Available-for-Sale - 12 Months or longer - Unrealized Losses	101	134
Securities Available-for-Sale - Fair Value	5,899	5,866
Securities Available-for-Sale - Unrealized Losses	101	134
Other Equity Securities [Member]
Securities Available-for-Sale
Securities Available-for-Sale - Less than 12 Months - Fair Value	175
Securities Available-for-Sale - Less than 12 Months - Unrealized Losses	325
Securities Available-for-Sale - Fair Value	175
Securities Available-for-Sale - Unrealized Losses	$ 325
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
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