Note 5 - Loans and the Allowance for Credit Losses - Analysis of Aging of Loans (Details) - USD ($) $ in Thousands	Mar. 31, 2024	Dec. 31, 2023
Gross loans	$ 8,304,101	$ 8,351,841
Nonaccrual	47,438	52,524
Financial Asset, 30 to 59 Days Past Due [Member]
Gross loans	3,061	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	23,600	0
Financial Asset, Past Due [Member]
Gross loans	74,099	77,707
Financial Asset, Not Past Due [Member]
Gross loans	8,230,002	8,274,134
Commercial Portfolio Segment [Member]
Gross loans	1,572,494	1,578,730
Nonaccrual	12,640	12,827
Commercial Portfolio Segment [Member] \| Financial Asset, 30 to 59 Days Past Due [Member]
Gross loans	495	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	13,135	13,382
Commercial Portfolio Segment [Member] \| Financial Asset, Not Past Due [Member]
Gross loans	1,559,359	1,565,348
Commercial Real Estate Portfolio Segment [Member]
Gross loans	5,829,950	5,895,545
Nonaccrual	33,275	36,192
Commercial Real Estate Portfolio Segment [Member] \| Financial Asset, 30 to 59 Days Past Due [Member]
Gross loans	525	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	33,800	36,719
Commercial Real Estate Portfolio Segment [Member] \| Financial Asset, Not Past Due [Member]
Gross loans	5,796,150	5,858,826
Commercial Construction Portfolio Segment [Member]
Gross loans	646,593	620,496
Nonaccrual	0	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	23,600	0
Commercial Construction Portfolio Segment [Member] \| Financial Asset, Past Due [Member]
Gross loans	23,600	23,600
Commercial Construction Portfolio Segment [Member] \| Financial Asset, Not Past Due [Member]
Gross loans	622,993	596,896
Residential Portfolio Segment [Member]
Gross loans	254,214	256,041
Nonaccrual	1,523	3,505
Residential Portfolio Segment [Member] \| Financial Asset, 30 to 59 Days Past Due [Member]
Gross loans	1,942	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	3,465	4,006
Residential Portfolio Segment [Member] \| Financial Asset, Not Past Due [Member]
Gross loans	250,749	252,035
Consumer Portfolio Segment [Member]
Gross loans	850	1,029
Nonaccrual	0	0
Consumer Portfolio Segment [Member] \| Financial Asset, 30 to 59 Days Past Due [Member]
Gross loans	99	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	99	0
Consumer Portfolio Segment [Member] \| Financial Asset, Not Past Due [Member]
Gross loans	$ 751	$ 1,029