Note 4 - Loans and Allowance for Loan Loss - Nonperforming Assets (Details) - USD ($)	Mar. 31, 2020	Dec. 31, 2019
Nonaccrual loans	$ 3,029,000	$ 2,901,000
Accruing loans past due 90 days or more		222,000
Nonperforming loans	2,900,000	3,000,000
Total Nonperforming Loans	974,650,000	952,496,000
Total Nonperforming Assets	$ 1,313,173,000	$ 1,321,537,000
Nonperforming Loans to Total Loans	0.54%	0.57%
Nonperforming Assets to Total Assets	0.42%	0.42%
Nonperforming Financial Instruments [Member]
Accruing loans past due 90 days or more	$ 3,029,000	$ 3,123,000
Nonperforming loans	2,203,000	2,259,000
Total Nonperforming Loans	5,232,000	5,382,000
Total Real Estate Owned	291,000	233,000
Total Nonperforming Assets	5,523,000	5,615,000
Residential Portfolio Segment [Member] \| Real Estate Sector [Member]
Nonaccrual loans	1,997,000	1,817,000
Accruing loans past due 90 days or more		196,000
Total Nonperforming Loans	346,864,000	347,766,000
Residential Portfolio Segment [Member] \| Real Estate Sector [Member] \| Nonperforming Financial Instruments [Member]
Nonperforming loans	503,000	511,000
Total Real Estate Owned	117,000	41,000
Commercial Portfolio Segment [Member] \| Real Estate Sector [Member]
Nonaccrual loans	161,000	234,000
Total Nonperforming Loans	354,374,000	351,360,000
Commercial Portfolio Segment [Member] \| Real Estate Sector [Member] \| Nonperforming Financial Instruments [Member]
Nonperforming loans	1,621,000	1,648,000
Total Real Estate Owned	174,000	192,000
Commercial Portfolio Segment [Member] \| Commercial and Industrial Sector [Member]
Nonaccrual loans	714,000	740,000
Total Nonperforming Loans	80,721,000	85,586,000
Commercial Portfolio Segment [Member] \| Commercial and Industrial Sector [Member] \| Nonperforming Financial Instruments [Member]
Nonaccrual loans	79,000	100,000
Consumer Portfolio Segment [Member]
Nonaccrual loans	157,000	110,000
Accruing loans past due 90 days or more		26,000
Total Nonperforming Loans	$ 121,494,000	$ 113,637,000

Reflects the percentage derived from dividing nonperforming assets by total assets.

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Sum of the carrying amounts as of the balance sheet date of all assets that are recognized. Assets are probable future economic benefits obtained or controlled by an entity as a result of past transactions or events.

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Amount of financing receivable modified as troubled debt restructuring.

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Carrying amount as of the balance sheet date of land and buildings obtained through foreclosure proceedings or defeasance in full or partial satisfaction of a debt arrangement.

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