Note 5 - Loans and the Allowance for Credit Losses - Analysis of Aging of Loans (Details) - USD ($) $ in Thousands	Dec. 31, 2024	Dec. 31, 2023
Gross loans	$ 8,280,482	$ 8,351,841
Nonaccrual	57,310	52,524
Financial Asset, 30 to 59 Days Past Due [Member]
Gross loans	3,331	1,357
Financial Asset, 60 to 89 Days Past Due [Member]
Gross loans	0	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	60,641	77,707
Financial Asset, Not Past Due [Member]
Gross loans	8,219,841	8,274,134
Commercial Portfolio Segment [Member]
Gross loans	1,532,730	1,578,730
Nonaccrual	16,231	12,827
Commercial Portfolio Segment [Member] | Financial Asset, 30 to 59 Days Past Due [Member]
Gross loans	1,340	555
Commercial Portfolio Segment [Member] | Financial Asset, 60 to 89 Days Past Due [Member]
Gross loans	0	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	17,571	13,382
Commercial Portfolio Segment [Member] | Financial Asset, Not Past Due [Member]
Gross loans	1,515,159	1,565,348
Commercial Real Estate Portfolio Segment [Member]
Gross loans	5,880,679	5,895,545
Nonaccrual	36,486	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	0	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	36,486	36,719
Commercial Real Estate Portfolio Segment [Member] | Financial Asset, Not Past Due [Member]
Gross loans	5,844,193	5,858,826
Commercial Construction Portfolio Segment [Member]
Gross loans	616,246	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	614,042	596,896
Residential Portfolio Segment [Member]
Gross loans	249,691	256,041
Nonaccrual	2,389	3,505
Residential Portfolio Segment [Member] | Financial Asset, 30 to 59 Days Past Due [Member]
Gross loans	1,991	275
Residential Portfolio Segment [Member] | Financial Asset, 60 to 89 Days Past Due [Member]
Gross loans	0	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	4,380	4,006
Residential Portfolio Segment [Member] | Financial Asset, Not Past Due [Member]
Gross loans	245,311	252,035
Consumer Portfolio Segment [Member]
Gross loans	1,136	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	$ 1,136	$ 1,029