Note 5 - Loans and the Allowance for Credit Losses - Analysis of Aging of Loans (Details) - USD ($) $ in Thousands	Jun. 30, 2024	Dec. 31, 2023
Gross loans	$ 8,162,500	$ 8,351,841
Nonaccrual	46,026	52,524
Financial Asset, 30 to 59 Days Past Due [Member]
Gross loans	1,667	1,357
Financial Asset, 60 to 89 Days Past Due [Member]
Gross loans	7,116	23,826
Financial Asset, Equal to or Greater than 90 Days Past Due [Member]
Gross loans	0	0
Financial Asset, Past Due [Member]
Gross loans	54,809	77,707
Financial Asset, Not Past Due [Member]
Gross loans	8,107,691	8,274,134
Commercial Portfolio Segment [Member]
Gross loans	1,501,732	1,578,730
Nonaccrual	12,778	12,827
Commercial Portfolio Segment [Member] | Financial Asset, 30 to 59 Days Past Due [Member]
Gross loans	1,667	555
Commercial Portfolio Segment [Member] | Financial Asset, 60 to 89 Days Past Due [Member]
Gross loans	427	0
Commercial Portfolio Segment [Member] | Financial Asset, Equal to or Greater than 90 Days Past Due [Member]
Gross loans	0	0
Commercial Portfolio Segment [Member] | Financial Asset, Past Due [Member]
Gross loans	14,872	13,382
Commercial Portfolio Segment [Member] | Financial Asset, Not Past Due [Member]
Gross loans	1,486,860	1,565,348
Commercial Real Estate Portfolio Segment [Member]
Gross loans	5,763,869	5,895,545
Nonaccrual	29,585	36,192
Commercial Real Estate Portfolio Segment [Member] | Financial Asset, 30 to 59 Days Past Due [Member]
Gross loans	0	527
Commercial Real Estate Portfolio Segment [Member] | Financial Asset, 60 to 89 Days Past Due [Member]
Gross loans	4,876	0
Commercial Real Estate Portfolio Segment [Member] | Financial Asset, Equal to or Greater than 90 Days Past Due [Member]
Gross loans	0	0
Commercial Real Estate Portfolio Segment [Member] | Financial Asset, Past Due [Member]
Gross loans	34,461	36,719
Commercial Real Estate Portfolio Segment [Member] | Financial Asset, Not Past Due [Member]
Gross loans	5,729,408	5,858,826
Commercial Construction Portfolio Segment [Member]
Gross loans	639,168	620,496
Nonaccrual	2,204	0
Commercial Construction Portfolio Segment [Member] | Financial Asset, 30 to 59 Days Past Due [Member]
Gross loans	0	0
Commercial Construction Portfolio Segment [Member] | Financial Asset, 60 to 89 Days Past Due [Member]
Gross loans	0	23,600
Commercial Construction Portfolio Segment [Member] | Financial Asset, Equal to or Greater than 90 Days Past Due [Member]
Gross loans	0	0
Commercial Construction Portfolio Segment [Member] | Financial Asset, Past Due [Member]
Gross loans	2,204	23,600
Commercial Construction Portfolio Segment [Member] | Financial Asset, Not Past Due [Member]
Gross loans	636,964	596,896
Residential Portfolio Segment [Member]
Gross loans	256,786	256,041
Nonaccrual	1,459	3,505
Residential Portfolio Segment [Member] | Financial Asset, 30 to 59 Days Past Due [Member]
Gross loans	0	275
Residential Portfolio Segment [Member] | Financial Asset, 60 to 89 Days Past Due [Member]
Gross loans	1,813	226
Residential Portfolio Segment [Member] | Financial Asset, Equal to or Greater than 90 Days Past Due [Member]
Gross loans	0	0
Residential Portfolio Segment [Member] | Financial Asset, Past Due [Member]
Gross loans	3,272	4,006
Residential Portfolio Segment [Member] | Financial Asset, Not Past Due [Member]
Gross loans	253,514	252,035
Consumer Portfolio Segment [Member]
Gross loans	945	1,029
Nonaccrual	0	0
Consumer Portfolio Segment [Member] | Financial Asset, 30 to 59 Days Past Due [Member]
Gross loans	0	0
Consumer Portfolio Segment [Member] | Financial Asset, 60 to 89 Days Past Due [Member]
Gross loans	0	0
Consumer Portfolio Segment [Member] | Financial Asset, Equal to or Greater than 90 Days Past Due [Member]
Gross loans	0	0
Consumer Portfolio Segment [Member] | Financial Asset, Past Due [Member]
Gross loans	0	0
Consumer Portfolio Segment [Member] | Financial Asset, Not Past Due [Member]
Gross loans	$ 945	$ 1,029