Note 3 - Investment Securities (Details Textual)	12 Months Ended
Dec. 31, 2017 USD ($)	Dec. 31, 2016 USD ($)	Dec. 31, 2015 USD ($)
Other than Temporary Impairment, Credit Losses Recognized in Earnings, Additions, Additional Credit Losses	$ 0	$ 7,000	$ 3,000
Available-for-sale Securities Pledged as Collateral	555,200,000	380,100,000
Securities, Continuous Loss Position, Accumulated Loss	20,100,000	19,100,000
Securities, Continuous Unrealized Loss Position, Fair Value	836,900,000	595,000,000
Proceeds from Sale of Available-for-sale Securities	31,197,000	78,585,000	11,707,000
Available-for-sale Securities, Gross Realized Gains	652,000	680,000	396,000
Available-for-sale Securities, Gross Realized Losses	798,000	24,000	288,000
Other Comprehensive Income (Loss), Reclassification Adjustment from AOCI for Sale of Securities, Tax	$ (52,000)	$ 236,000	$ 39,000
US Government Agencies Debt Securities [Member]
Available-for-sale, Securities in Unrealized Loss Positions, Qualitative Disclosure, Number of Positions	11
Collateralized Mortgage Obligations [Member]
Available-for-sale, Securities in Unrealized Loss Positions, Qualitative Disclosure, Number of Positions	74
Number of Securities in Investment Portfolio	0	0
Collateralized Mortgage Obligations [Member] \| AltA [Member]
Number of Securities in Investment Portfolio	0	0
Collateralized Mortgage Obligations [Member] \| Subprime [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	26
Asset-backed Securities [Member]
Available-for-sale, Securities in Unrealized Loss Positions, Qualitative Disclosure, Number of Positions	0
Corporate Debt Securities [Member]
Available-for-sale, Securities in Unrealized Loss Positions, Qualitative Disclosure, Number of Positions	6
Collateralized Debt Obligations [Member]
Proceeds from Sale of Available-for-sale Securities	$ 1,500,000
Available-for-sale Securities, Gross Realized Losses	798,000
Other Comprehensive Income (Loss), Reclassification Adjustment from AOCI for Sale of Securities, Tax	(287,000)
Available-for-sale Securities, Gross Realized Gain (Loss)	$ (798,000)
Mortgage-backed Securities, Issued by Private Enterprises [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
Mortgage-backed Securities, Issued by Private Enterprises [Member] \| Subprime [Member]
Number of Securities in Investment Portfolio	0	0
US States and Political Subdivisions Debt Securities [Member]
Available-for-sale, Securities in Unrealized Loss Positions, Qualitative Disclosure, Number of Positions	12

Refers to number of securities included in investment portfolio.

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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.

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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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This item represents the difference between the gross realized gains and losses realized on the sale of debt or equity securities categorized neither as held-to-maturity nor trading securities. Additionally, this item would include any losses recognized for other than temporary impairments (OTTI) of the subject investments in debt and equity securities.

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This item represents the gross profit realized on the sale of debt or equity securities categorized neither as held-to-maturity nor trading securities.

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This item represents the gross loss realized on the sale of debt or equity securities categorized neither as held-to-maturity nor trading securities.

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- Definition

The fair value of available-for-sale securities that serve as collateral for borrowings.

+ References

Reference 1: http://www.xbrl.org/2003/role/presentationRef
-Publisher FASB
-Name Accounting Standards Codification
-Topic 310
-SubTopic 10
-Section 50
-Paragraph 5
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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://www.xbrl.org/2003/role/presentationRef
-Publisher FASB
-Name Accounting Standards Codification
-Topic 320
-SubTopic 10
-Section 50
-Paragraph 6
-Subparagraph (b)(3)
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- Definition

Amount of tax expense (benefit) of reclassification adjustment from accumulated other comprehensive income for unrealized gain (loss) realized upon the sale of available-for-sale securities.

+ References

Reference 1: http://www.xbrl.org/2003/role/presentationRef
-Publisher FASB
-Name Accounting Standards Codification
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-SubTopic 10
-Section 50
-Paragraph 9
-Subparagraph (d)
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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

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-Topic 320
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-Section 50
-Paragraph 8B
-Subparagraph (e)
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- Definition

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

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Reference 1: http://www.xbrl.org/2003/role/presentationRef
-Publisher FASB
-Name Accounting Standards Codification
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