Note 6 - Temporarily Impaired Securities (Details) - USD ($) $ in Thousands	Jun. 30, 2016	Dec. 31, 2015
Collateralized Mortgage Backed Securities [Member]
Temporarily Impaired Securities, Less than 12 months, Fair Value	$ 1,724	$ 1,025,342
Temporarily Impaired Securities, Less than 12 months, Unrealized Losses	5	11,398
Temporarily Impaired Securities, 12 months or longer Fair Value	39	6
Temporarily Impaired Securities, 12 months or longer Unrealized Losses	1	1
Temporarily impaired securities, Total fair value	1,763	1,025,348
Temporarily impaired securities, Total unrealized losses	6	11,399
US Treasury Securities [Member]
Temporarily Impaired Securities, Less than 12 months, Fair Value		224,289
Temporarily Impaired Securities, Less than 12 months, Unrealized Losses		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		224,289
Temporarily impaired securities, Total unrealized losses		395
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	32	36
Temporarily Impaired Securities, 12 months or longer Unrealized Losses	24	27
Temporarily impaired securities, Total fair value	32	36
Temporarily impaired securities, Total unrealized losses	24	27
US Government-sponsored Enterprises Debt Securities [Member]
Temporarily Impaired Securities, Less than 12 months, Fair Value		148,160
Temporarily Impaired Securities, Less than 12 months, Unrealized Losses		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		148,160
Temporarily impaired securities, Total unrealized losses		1,840
Corporate Debt Securities [Member]
Temporarily Impaired Securities, Less than 12 months, Fair Value	9,847	9,950
Temporarily Impaired Securities, Less than 12 months, Unrealized Losses	153	50
Temporarily Impaired Securities, 12 months or longer Fair Value	43,374	43,525
Temporarily Impaired Securities, 12 months or longer Unrealized Losses	1,626	1,475
Temporarily impaired securities, Total fair value	53,221	53,475
Temporarily impaired securities, Total unrealized losses	1,779	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	5,953	5,833
Temporarily Impaired Securities, 12 months or longer Unrealized Losses	47	167
Temporarily impaired securities, Total fair value	5,953	5,833
Temporarily impaired securities, Total unrealized losses	47	167
Preferred Stock of Government Sponsored Entities [Member]
Temporarily Impaired Securities, Less than 12 months, Fair Value		2,488
Temporarily Impaired Securities, Less than 12 months, Unrealized Losses		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		2,488
Temporarily impaired securities, Total unrealized losses		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	11,571	1,410,387
Temporarily Impaired Securities, Less than 12 months, Unrealized Losses	158	14,253
Temporarily Impaired Securities, 12 months or longer Fair Value	49,398	49,400
Temporarily Impaired Securities, 12 months or longer Unrealized Losses	1,698	1,670
Temporarily impaired securities, Total fair value	60,969	1,459,787
Temporarily impaired securities, Total unrealized losses	$ 1,856	$ 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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Reference 1: http://www.xbrl.org/2003/role/presentationRef
-Publisher FASB
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-Section 50
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-URI http://asc.fasb.org/extlink&oid=73527792&loc=d3e27337-111563

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