Note 4 - Loans - Allowance for Loan Losses by Portfolio Segment and Based on Impairment Method (Details) - USD ($) $ in Thousands	Dec. 31, 2019	Dec. 31, 2018
Loans individually evaluated for impairment, allowance	$ 3,236	$ 3,802
Loans individually evaluated for impairment, balance	75,859	106,886
Loans collectively evaluated for impairment, allowance	119,988	118,589
Loans collectively evaluated for impairment, balance	14,999,622	13,888,902
Loans, allowance	123,224	122,391
Loans	15,075,481	13,995,788
Commercial Portfolio Segment [Member]
Loans individually evaluated for impairment, allowance	2,543	1,837
Loans individually evaluated for impairment, balance	24,596	36,940
Loans collectively evaluated for impairment, allowance	54,478	53,141
Loans collectively evaluated for impairment, balance	2,754,148	2,705,025
Loans, allowance	57,021	54,978
Loans	2,778,744	2,741,965
Real Estate Construction Portfolio Segment [Member]
Loans individually evaluated for impairment, allowance	0	0
Loans individually evaluated for impairment, balance	4,580	4,873
Loans collectively evaluated for impairment, allowance	19,474	19,626
Loans collectively evaluated for impairment, balance	575,284	576,581
Loans, allowance	19,474	19,626
Loans	579,864	581,454
Commercial Real Estate Portfolio Segment [Member]
Loans individually evaluated for impairment, allowance	473	877
Loans individually evaluated for impairment, balance	35,070	51,471
Loans collectively evaluated for impairment, allowance	33,129	32,610
Loans collectively evaluated for impairment, balance	7,240,192	6,672,729
Loans, allowance	33,602	33,487
Loans	7,275,262	6,724,200
Residential Mortgage and Equity Lines Portfolio Segment [Member]
Loans individually evaluated for impairment, allowance	220	1,088
Loans individually evaluated for impairment, balance	11,613	13,602
Loans collectively evaluated for impairment, allowance	12,888	13,194
Loans collectively evaluated for impairment, balance	4,424,948	3,930,218
Loans, allowance	13,108	14,282
Loans	4,436,561	3,943,820
Consumer Portfolio Segment [Member]
Loans individually evaluated for impairment, allowance	0	0
Loans individually evaluated for impairment, balance	0	0
Loans collectively evaluated for impairment, allowance	19	18
Loans collectively evaluated for impairment, balance	5,050	4,349
Loans, allowance	19	18
Loans	$ 5,050	$ 4,349

The valuation allowance for financing receivables that are expected to be uncollectible that were collectively evaluated for impairment.

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-Name Accounting Standards Codification
-Topic 310
-SubTopic 10
-Section 50
-Paragraph 11B
-Subparagraph (g)
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Amount of valuation allowance for financing receivables that are expected to be uncollectible that were individually evaluated for impairment.

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Amount of allowance to cover probable credit losses on loans and leases. Includes carryover of or adjustments to the allowance for loan losses in connection with business combinations. Excludes allowance for loans and leases covered under loss sharing agreements.

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Amount before allowance of loans and leases held in portfolio, including but not limited to, commercial and consumer loans. Includes deferred interest and fees, undisbursed portion of loan balance, unamortized costs and premiums and discounts from face amounts. Excludes loans and leases covered under loss sharing agreements.

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