Note 4 - Investment Securities (Details) - Temporarily Impaired Securities $ in Thousands	12 Months Ended
Dec. 31, 2015 USD ($)	Dec. 31, 2014 USD ($)
Securities Available-for-Sale
Securities Available-for-Sale - Less than 12 Months - Fair Value	$ 1,410,387	$ 376,601
Securities Available-for-Sale - Less than 12 Months - Unrealized Losses	$ 14,253	$ 3,998
Securities Available-for-Sale - Less than 12 Months - No. of Issuances	47	8
Securities Available-for-Sale - 12 Months or longer - Fair Value	$ 49,400	$ 494,754
Securities Available-for-Sale - 12 Months or longer - Unrealized Losses	$ 1,670	$ 7,801
Securities Available-for-Sale - 12 Months or longer - No. of issuances	7	22
Securities Available-for-Sale - Fair Value	$ 1,459,787	$ 871,355
Securities Available-for-Sale - Unrealized Losses	$ 15,923	$ 11,799
Securities Available-for-Sale - No. of issuances	54	30
US Treasury Securities [Member]
Securities Available-for-Sale
Securities Available-for-Sale - Less than 12 Months - Fair Value	$ 224,289	$ 374,153
Securities Available-for-Sale - Less than 12 Months - Unrealized Losses	$ 395	$ 265
Securities Available-for-Sale - Less than 12 Months - No. of Issuances	5	6
Securities Available-for-Sale - Fair Value	$ 224,289	$ 374,153
Securities Available-for-Sale - Unrealized Losses	$ 395	$ 265
Securities Available-for-Sale - No. of issuances	5	6
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 - Less than 12 Months - No. of Issuances	3
Securities Available-for-Sale - Fair Value	$ 148,160
Securities Available-for-Sale - Unrealized Losses	$ 1,840
Securities Available-for-Sale - No. of issuances	3
Collateralized Mortgage Backed Securities [Member]
Securities Available-for-Sale
Securities Available-for-Sale - Less than 12 Months - Fair Value	$ 1,025,342
Securities Available-for-Sale - Less than 12 Months - Unrealized Losses	$ 11,398
Securities Available-for-Sale - Less than 12 Months - No. of Issuances	35
Securities Available-for-Sale - 12 Months or longer - Fair Value	$ 6	$ 425,090
Securities Available-for-Sale - 12 Months or longer - Unrealized Losses	$ 1	$ 6,386
Securities Available-for-Sale - 12 Months or longer - No. of issuances	2	16
Securities Available-for-Sale - Fair Value	$ 1,025,348	$ 425,090
Securities Available-for-Sale - Unrealized Losses	$ 11,399	$ 6,386
Securities Available-for-Sale - No. of issuances	37	16
Collateralized Mortgage Obligations [Member]
Securities Available-for-Sale
Securities Available-for-Sale - 12 Months or longer - Fair Value	$ 36	$ 45
Securities Available-for-Sale - 12 Months or longer - Unrealized Losses	$ 27	$ 34
Securities Available-for-Sale - 12 Months or longer - No. of issuances	1	1
Securities Available-for-Sale - Fair Value	$ 36	$ 45
Securities Available-for-Sale - Unrealized Losses	$ 27	$ 34
Securities Available-for-Sale - No. of issuances	1	1
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 - Less than 12 Months - No. of Issuances	1
Securities Available-for-Sale - 12 Months or longer - Fair Value	$ 43,525	$ 63,753
Securities Available-for-Sale - 12 Months or longer - Unrealized Losses	$ 1,475	$ 1,247
Securities Available-for-Sale - 12 Months or longer - No. of issuances	3	4
Securities Available-for-Sale - Fair Value	$ 53,475	$ 63,753
Securities Available-for-Sale - Unrealized Losses	$ 1,525	$ 1,247
Securities Available-for-Sale - No. of issuances	4	4
Mutual Funds [Member]
Securities Available-for-Sale
Securities Available-for-Sale - 12 Months or longer - Fair Value	$ 5,833	$ 5,866
Securities Available-for-Sale - 12 Months or longer - Unrealized Losses	$ 167	$ 134
Securities Available-for-Sale - 12 Months or longer - No. of issuances	1	1
Securities Available-for-Sale - Fair Value	$ 5,833	$ 5,866
Securities Available-for-Sale - Unrealized Losses	$ 167	$ 134
Securities Available-for-Sale - No. of issuances	1	1
Preferred Stock of Government Sponsored Entities [Member]
Securities Available-for-Sale
Securities Available-for-Sale - Less than 12 Months - Fair Value	$ 2,488	$ 2,448
Securities Available-for-Sale - Less than 12 Months - Unrealized Losses	$ 228	$ 3,733
Securities Available-for-Sale - Less than 12 Months - No. of Issuances	2	2
Securities Available-for-Sale - Fair Value	$ 2,488	$ 2,448
Securities Available-for-Sale - Unrealized Losses	$ 228	$ 3,733
Securities Available-for-Sale - No. of issuances	2	2
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 - Less than 12 Months - No. of Issuances	1
Securities Available-for-Sale - Fair Value	$ 158
Securities Available-for-Sale - Unrealized Losses	$ 342
Securities Available-for-Sale - No. of issuances	1

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