Note 6 - Loans and the Allowance for Credit Losses - Analysis of Aging of Loans (Details) - USD ($) $ in Thousands	Sep. 30, 2024	Dec. 31, 2023
Gross loans	$ 8,116,332	$ 8,351,841
Nonaccrual	51,300	52,524
Financial Asset, 30 to 59 Days Past Due [Member]
Gross loans	5,119	1,357
Financial Asset, 60 to 89 Days Past Due [Member]
Gross loans	7,870	23,826
Financial Asset, Equal to or Greater than 90 Days Past Due [Member]
Gross loans	3,165	0
Financial Asset, Past Due [Member]
Gross loans	67,454	77,707
Financial Asset, Not Past Due [Member]
Gross loans	8,048,878	8,274,134
Commercial Portfolio Segment [Member]
Gross loans	1,513,991	1,578,730
Nonaccrual	12,693	12,827
Commercial Portfolio Segment [Member] \| Financial Asset, 30 to 59 Days Past Due [Member]
Gross loans	5,047	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	17,740	13,382
Commercial Portfolio Segment [Member] \| Financial Asset, Not Past Due [Member]
Gross loans	1,496,251	1,565,348
Commercial Real Estate Portfolio Segment [Member]
Gross loans	5,735,170	5,895,545
Nonaccrual	33,219	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	7,870	0
Commercial Real Estate Portfolio Segment [Member] \| Financial Asset, Equal to or Greater than 90 Days Past Due [Member]
Gross loans	3,165	0
Commercial Real Estate Portfolio Segment [Member] \| Financial Asset, Past Due [Member]
Gross loans	44,254	36,719
Commercial Real Estate Portfolio Segment [Member] \| Financial Asset, Not Past Due [Member]
Gross loans	5,690,916	5,858,826
Commercial Construction Portfolio Segment [Member]
Gross loans	616,087	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	613,883	596,896
Residential Portfolio Segment [Member]
Gross loans	250,249	256,041
Nonaccrual	3,184	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	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	3,184	4,006
Residential Portfolio Segment [Member] \| Financial Asset, Not Past Due [Member]
Gross loans	247,065	252,035
Consumer Portfolio Segment [Member]
Gross loans	835	1,029
Nonaccrual	0	0
Consumer Portfolio Segment [Member] \| Financial Asset, 30 to 59 Days Past Due [Member]
Gross loans	72	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	72	0
Consumer Portfolio Segment [Member] \| Financial Asset, Not Past Due [Member]
Gross loans	$ 763	$ 1,029