Note 5 - Investment Securities (Details Textual) $ in Thousands	3 Months Ended
Mar. 31, 2018 USD ($)	Mar. 31, 2017 USD ($)	Dec. 31, 2017 USD ($)
Other than Temporary Impairment, Credit Losses Recognized in Earnings, Additions, Additional Credit Losses	$ 0	$ 0
Securities, Continuous Loss Position, Accumulated Loss	35,400		$ 20,100
Securities, Continuous Unrealized Loss Position, Fair Value	970,400		$ 836,900
Proceeds from Sale of Available-for-sale Securities, Total	$ 0	$ 0
Mortgage-backed Securities, Issued by Private Enterprises [Member]
Number of Securities in Investment Portfolio	0		0
Mortgage-backed Securities, Issued by Private Enterprises [Member] \| Subprime [Member]
Number of Securities in Investment Portfolio	0		0
Mortgage-backed Securities, Issued by Private Enterprises [Member] \| AltA [Member]
Number of Securities in Investment Portfolio	0		0
US Government Agencies Debt Securities [Member]
Available-for-sale, Securities in Unrealized Loss Positions, Qualitative Disclosure, Number of Positions, Total	14
Collateralized Mortgage Obligations [Member]
Number of Securities in Investment Portfolio	0		0
Available-for-sale, Securities in Unrealized Loss Positions, Qualitative Disclosure, Number of Positions, Total	85
Collateralized Mortgage Obligations [Member] \| Subprime [Member]
Number of Securities in Investment Portfolio	0		0
Collateralized Mortgage Obligations [Member] \| AltA [Member]
Number of Securities in Investment Portfolio	0		0
Collateralized Mortgage Backed Securities [Member]
Available-for-sale, Securities in Unrealized Loss Positions, Qualitative Disclosure, Number of Positions, Total	29
US States and Political Subdivisions Debt Securities [Member]
Available-for-sale, Securities in Unrealized Loss Positions, Qualitative Disclosure, Number of Positions, Total	20
Asset-backed Securities [Member]
Available-for-sale, Securities in Unrealized Loss Positions, Qualitative Disclosure, Number of Positions, Total	2
Corporate Debt Securities [Member]
Available-for-sale, Securities in Unrealized Loss Positions, Qualitative Disclosure, Number of Positions, Total	7

Refers to number of securities included in investment portfolio.

No definition available.

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- Definition

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

+ References

No definition available.

+ Details

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- Definition

This item represents the fair value of securities categorized as held-to-maturity and available-for-sale which are in an unrealized loss position.

+ References

No definition available.

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- Definition

Number of investment positions in available-for-sale investments in a continuous unrealized loss position for which an other-than-temporary impairment (OTTI) has not been recognized in the income statement.

+ References

Reference 1: http://fasb.org/us-gaap/role/ref/legacyRef
-Publisher FASB
-Name Accounting Standards Codification
-Topic 320
-SubTopic 10
-Section 50
-Paragraph 6
-Subparagraph (b)(3)
-URI http://asc.fasb.org/extlink&oid=82897076&loc=d3e27290-111563

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This item represents an increase to the cumulative amount of credit losses recognized in earnings for an other than temporary impairment (OTTI) of a debt security held for which a previous OTTI was recognized and the investor does not intend to sell the debt security and it is not more likely than not that the investor will be required to sell the debt security before recovery of its amortized cost basis.

+ References

Reference 1: http://fasb.org/us-gaap/role/ref/legacyRef
-Publisher FASB
-Name Accounting Standards Codification
-Topic 320
-SubTopic 10
-Section 50
-Paragraph 8B
-Subparagraph (e)
-URI http://asc.fasb.org/extlink&oid=82897076&loc=SL6284393-111563

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- Definition

The cash inflow associated with the sale of debt and equity securities classified as available-for-sale securities.

+ References

Reference 1: http://fasb.org/us-gaap/role/ref/legacyRef
-Publisher FASB
-Name Accounting Standards Codification
-Topic 320
-SubTopic 10
-Section 45
-Paragraph 11
-URI http://asc.fasb.org/extlink&oid=109979856&loc=d3e26853-111562

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-Publisher FASB
-Name Accounting Standards Codification
-Topic 230
-SubTopic 10
-Section 45
-Paragraph 12
-Subparagraph (a),(b)
-URI http://asc.fasb.org/extlink&oid=109223946&loc=d3e3179-108585

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