Note 3 - Investment Securities (Details Textual)	1 Months Ended	12 Months Ended
Dec. 31, 2018 USD ($)	Dec. 31, 2019 USD ($)	Dec. 31, 2018 USD ($)	Dec. 31, 2017 USD ($)
Other than Temporary Impairment, Credit Losses Recognized in Earnings, Additions, Additional Credit Losses		$ 0	$ 0	$ 0
Debt Securities, Available-for-sale, Restricted	$ 710,700,000	847,100,000	710,700,000
Securities, Continuous Loss Position, Accumulated Loss	21,300,000	5,900,000	21,300,000
Securities, Continuous Unrealized Loss Position, Fair Value	674,300,000	353,200,000	674,300,000
Proceeds from Sale of Available-for-sale Securities, Total		54,742,000	6,439,000	31,197,000
Debt Securities, Available-for-sale, Realized Gain		1,200,000
Debt Securities, Available-for-sale, Realized Loss		67,000
Debt Securities, Available-for-sale, Realized Gain (Loss), Total		1,100,000
Other Comprehensive Income (Loss), Reclassification Adjustment from AOCI for Sale of Securities, Tax, Total		280,000	18,000	(52,000)
Available-for-sale Securities, Gross Realized Losses			67,000	798,000
Available-for-sale Securities, Gross Realized Gains				652,000
Debt Securities, Available-for-sale, Transfer, Amount	230,100,000		230,100,000
Other Comprehensive Income (Loss), Available-for-sale Securities, Transferred to Held-to-maturity, before Tax	$ 9,400,000	0	$ (9,362,000)	0
Unrealized Loss Associated with Transferred Securities		$ 8,100,000
Mortgage-backed Securities, Issued by Private Enterprises [Member]
Number of Securities in Investment Portfolio	0	0	0
Mortgage-backed Securities, Issued by Private Enterprises [Member] \| Subprime [Member]
Number of Securities in Investment Portfolio	0	0	0
Mortgage-backed Securities, Issued by Private Enterprises [Member] \| AltA [Member]
Number of Securities in Investment Portfolio	0	0	0
Collateralized Mortgage Obligations [Member]
Number of Securities in Investment Portfolio	0	0	0
Available-for-sale, Securities in Unrealized Loss Positions, Qualitative Disclosure, Number of Positions, Total	23	32	23
Proceeds from Sale of Available-for-sale Securities, Total			$ 660,000	1,500,000
Other Comprehensive Income (Loss), Reclassification Adjustment from AOCI for Sale of Securities, Tax, Total			17,000	(287,000)
Available-for-sale Securities, Gross Realized Losses			$ 66,000	$ 798,000
Collateralized Mortgage Obligations [Member] \| Subprime [Member]
Number of Securities in Investment Portfolio	0	0	0
Collateralized Mortgage Obligations [Member] \| AltA [Member]
Number of Securities in Investment Portfolio	0	0	0
US Government Agencies Debt Securities [Member]
Available-for-sale, Securities in Unrealized Loss Positions, Qualitative Disclosure, Number of Positions, Total		9
Collateralized Mortgage Backed Securities [Member]
Available-for-sale, Securities in Unrealized Loss Positions, Qualitative Disclosure, Number of Positions, Total	2	17	2
US States and Political Subdivisions Debt Securities [Member]
Available-for-sale, Securities in Unrealized Loss Positions, Qualitative Disclosure, Number of Positions, Total		0
Asset-backed Securities [Member]
Available-for-sale, Securities in Unrealized Loss Positions, Qualitative Disclosure, Number of Positions, Total		7
Corporate Debt Securities [Member]
Available-for-sale, Securities in Unrealized Loss Positions, Qualitative Disclosure, Number of Positions, Total	1		1

Fair value amount of available-for-sale securities transferred to held-to-maturity.

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Refers to number of securities included in investment portfolio.

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Amount before tax, after reclassification adjustments, of appreciation (loss) in value of available-for-sale securities transferred to held-to-maturity, attributable to parent entity.

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

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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.

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The amount of unrealized loss associated with the transferred 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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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.

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Amount of realized gain on investment in debt security measured at fair value with change in fair value recognized in other comprehensive income (available-for-sale).

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Amount of realized gain (loss) on investment in debt security measured at fair value with change in fair value recognized in other comprehensive income (available-for-sale).

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Amount of realized loss on investment in debt security measured at fair value with change in fair value recognized in other comprehensive income (available-for-sale).

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Amount of restricted investment in debt security measured at fair value with change in fair value recognized in other comprehensive income (available-for-sale).

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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.

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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.

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

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