Note 6 - Investment Securities - Temporarily Impaired Securities (Details) - USD ($) $ in Thousands	Sep. 30, 2016	Dec. 31, 2015
US Treasury Securities [Member]
Temporarily Impaired Securities, Less than 12 months, Fair Value	$ 149,983	$ 224,289
Temporarily Impaired Securities, Less than 12 months, Unrealized Losses	24	395
Temporarily Impaired Securities, 12 months or longer Fair Value
Temporarily Impaired Securities, 12 months or longer Unrealized Losses
Temporarily impaired securities, Total fair value	149,983	224,289
Temporarily impaired securities, Total unrealized losses	24	395
US Government-sponsored Enterprises Debt Securities [Member]
Temporarily Impaired Securities, Less than 12 months, Fair Value	149,931	148,160
Temporarily Impaired Securities, Less than 12 months, Unrealized Losses	69	1,840
Temporarily Impaired Securities, 12 months or longer Fair Value
Temporarily Impaired Securities, 12 months or longer Unrealized Losses
Temporarily impaired securities, Total fair value	149,931	148,160
Temporarily impaired securities, Total unrealized losses	69	1,840
Collateralized Mortgage Backed Securities [Member]
Temporarily Impaired Securities, Less than 12 months, Fair Value	44	1,025,342
Temporarily Impaired Securities, Less than 12 months, Unrealized Losses	1	11,398
Temporarily Impaired Securities, 12 months or longer Fair Value	265	6
Temporarily Impaired Securities, 12 months or longer Unrealized Losses	1	1
Temporarily impaired securities, Total fair value	309	1,025,348
Temporarily impaired securities, Total unrealized losses	2	11,399
Collateralized Mortgage Obligations [Member]
Temporarily Impaired Securities, Less than 12 months, Fair Value
Temporarily Impaired Securities, Less than 12 months, Unrealized Losses
Temporarily Impaired Securities, 12 months or longer Fair Value	30	36
Temporarily Impaired Securities, 12 months or longer Unrealized Losses	22	27
Temporarily impaired securities, Total fair value	30	36
Temporarily impaired securities, Total unrealized losses	22	27
Corporate Debt Securities [Member]
Temporarily Impaired Securities, Less than 12 months, Fair Value		9,950
Temporarily Impaired Securities, Less than 12 months, Unrealized Losses		50
Temporarily Impaired Securities, 12 months or longer Fair Value	54,063	43,525
Temporarily Impaired Securities, 12 months or longer Unrealized Losses	937	1,475
Temporarily impaired securities, Total fair value	54,063	53,475
Temporarily impaired securities, Total unrealized losses	937	1,525
Mutual Funds [Member]
Temporarily Impaired Securities, Less than 12 months, Fair Value
Temporarily Impaired Securities, Less than 12 months, Unrealized Losses
Temporarily Impaired Securities, 12 months or longer Fair Value	5,926	5,833
Temporarily Impaired Securities, 12 months or longer Unrealized Losses	74	167
Temporarily impaired securities, Total fair value	5,926	5,833
Temporarily impaired securities, Total unrealized losses	74	167
Preferred Stock of Government Sponsored Entities [Member]
Temporarily Impaired Securities, Less than 12 months, Fair Value	2,528	2,488
Temporarily Impaired Securities, Less than 12 months, Unrealized Losses	188	228
Temporarily Impaired Securities, 12 months or longer Fair Value
Temporarily Impaired Securities, 12 months or longer Unrealized Losses
Temporarily impaired securities, Total fair value	2,528	2,488
Temporarily impaired securities, Total unrealized losses	188	228
Other Equity Securities [Member]
Temporarily Impaired Securities, Less than 12 months, Fair Value		158
Temporarily Impaired Securities, Less than 12 months, Unrealized Losses		342
Temporarily Impaired Securities, 12 months or longer Fair Value
Temporarily Impaired Securities, 12 months or longer Unrealized Losses
Temporarily impaired securities, Total fair value		158
Temporarily impaired securities, Total unrealized losses		342
Temporarily Impaired Securities, Less than 12 months, Fair Value	302,486	1,410,387
Temporarily Impaired Securities, Less than 12 months, Unrealized Losses	282	14,253
Temporarily Impaired Securities, 12 months or longer Fair Value	60,284	49,400
Temporarily Impaired Securities, 12 months or longer Unrealized Losses	1,034	1,670
Temporarily impaired securities, Total fair value	362,770	1,459,787
Temporarily impaired securities, Total unrealized losses	$ 1,316	$ 15,923

Amount of accumulated unrealized loss on investments in debt and equity securities classified as available-for-sale that have been in a continuous loss position for twelve months or longer.

Reference 1: http://www.xbrl.org/2003/role/presentationRef
-Publisher FASB
-Name Accounting Standards Codification
-Topic 320
-SubTopic 10
-Section 50
-Paragraph 6
-Subparagraph (a)(2)
-URI http://asc.fasb.org/extlink&oid=73527792&loc=d3e27290-111563

Reference 2: http://www.xbrl.org/2003/role/presentationRef
-Publisher FASB
-Name Accounting Standards Codification
-Topic 320
-SubTopic 10
-Section 50
-Paragraph 7
-URI http://asc.fasb.org/extlink&oid=73527792&loc=d3e27337-111563

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Amount of accumulated unrealized loss on investments in debt and equity securities classified as available-for-sale in a continuous loss position.

+ References

Reference 1: http://www.xbrl.org/2003/role/presentationRef
-Publisher FASB
-Name Accounting Standards Codification
-Topic 320
-SubTopic 10
-Section 50
-Paragraph 7
-URI http://asc.fasb.org/extlink&oid=73527792&loc=d3e27337-111563

Reference 2: http://www.xbrl.org/2003/role/presentationRef
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-Publisher FASB
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