Note 6 - Investment Securities - Investment Securities (Details) - USD ($) $ in Thousands	Sep. 30, 2016	Dec. 31, 2015
US Treasury Securities [Member]
Securities Available-for-Sale, Amortized Cost	$ 389,921	$ 284,678
Securities Available-for-Sale, Gross Unrealized Gains	112	5
Securities Available-for-Sale, Gross Unrealized Losses	24	395
Available-for-sale Securities	390,009	284,288
US Government-sponsored Enterprises Debt Securities [Member]
Securities Available-for-Sale, Amortized Cost	250,000	150,000
Securities Available-for-Sale, Gross Unrealized Gains	79
Securities Available-for-Sale, Gross Unrealized Losses	69	1,840
Available-for-sale Securities	250,010	148,160
Collateralized Mortgage Backed Securities [Member]
Securities Available-for-Sale, Amortized Cost	556,454	1,073,108
Securities Available-for-Sale, Gross Unrealized Gains	7,186	560
Securities Available-for-Sale, Gross Unrealized Losses	2	11,399
Available-for-sale Securities	563,638	1,062,269
Collateralized Mortgage Obligations [Member]
Securities Available-for-Sale, Amortized Cost	52	63
Securities Available-for-Sale, Gross Unrealized Gains
Securities Available-for-Sale, Gross Unrealized Losses	22	27
Available-for-sale Securities	30	36
Corporate Debt Securities [Member]
Securities Available-for-Sale, Amortized Cost	74,962	74,955
Securities Available-for-Sale, Gross Unrealized Gains	444	425
Securities Available-for-Sale, Gross Unrealized Losses	937	1,525
Available-for-sale Securities	74,469	73,855
Mutual Funds [Member]
Securities Available-for-Sale, Amortized Cost	6,000	6,000
Securities Available-for-Sale, Gross Unrealized Gains
Securities Available-for-Sale, Gross Unrealized Losses	74	167
Available-for-sale Securities	5,926	5,833
Preferred Stock of Government Sponsored Entities [Member]
Securities Available-for-Sale, Amortized Cost	2,811	2,811
Securities Available-for-Sale, Gross Unrealized Gains	565	633
Securities Available-for-Sale, Gross Unrealized Losses	188	228
Available-for-sale Securities	3,188	3,216
Other Equity Securities [Member]
Securities Available-for-Sale, Amortized Cost	3,608	4,108
Securities Available-for-Sale, Gross Unrealized Gains	7,591	4,929
Securities Available-for-Sale, Gross Unrealized Losses		342
Available-for-sale Securities	11,199	8,695
Securities Available-for-Sale, Amortized Cost	1,283,808	1,595,723
Securities Available-for-Sale, Gross Unrealized Gains	15,977	6,552
Securities Available-for-Sale, Gross Unrealized Losses	1,316	15,923
Available-for-sale Securities	$ 1,298,469	$ 1,586,352

Amount of investment in debt and equity securities categorized neither as held-to-maturity nor trading.

Reference 1: http://www.xbrl.org/2003/role/presentationRef
-Publisher FASB
-Name Accounting Standards Codification
-Topic 320
-SubTopic 10
-Section 25
-Paragraph 1
-Subparagraph (b)
-URI http://asc.fasb.org/extlink&oid=65884222&loc=d3e22054-111558

Reference 2: http://www.xbrl.org/2003/role/presentationRef
-Publisher FASB
-Name Accounting Standards Codification
-Topic 320
-SubTopic 10
-Section 50
-Paragraph 5
-Subparagraph (aa)
-URI http://asc.fasb.org/extlink&oid=73527792&loc=d3e27232-111563

Reference 3: http://www.xbrl.org/2003/role/presentationRef
-Publisher FASB
-Name Accounting Standards Codification
-Topic 320
-SubTopic 10
-Section 45
-Paragraph 1
-URI http://asc.fasb.org/extlink&oid=66010992&loc=d3e26610-111562

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Amount before tax of unrealized gain in accumulated other comprehensive income (AOCI) on investments in debt and equity securities classified as available-for-sale.

+ References

Reference 1: http://www.xbrl.org/2003/role/presentationRef
-Publisher FASB
-Name Accounting Standards Codification
-Topic 320
-SubTopic 10
-Section 50
-Paragraph 2
-Subparagraph (b)
-URI http://asc.fasb.org/extlink&oid=73527792&loc=d3e27161-111563

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Amount before tax of unrealized loss in accumulated other comprehensive income (AOCI) on investments in debt and equity securities classified as available-for-sale.

+ References

Reference 1: http://www.xbrl.org/2003/role/presentationRef
-Publisher FASB
-Name Accounting Standards Codification
-Topic 320
-SubTopic 10
-Section 50
-Paragraph 2
-Subparagraph (c)
-URI http://asc.fasb.org/extlink&oid=73527792&loc=d3e27161-111563

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+ References

Reference 1: http://www.xbrl.org/2003/role/presentationRef
-Publisher FASB
-Name Accounting Standards Codification
-Topic 210
-SubTopic 10
-Section S99
-Paragraph 1
-Subparagraph (SX 210.5-02.2)
-URI http://asc.fasb.org/extlink&oid=6877327&loc=d3e13212-122682

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