Note 6 - Loans and the Allowance for Credit Losses - Analysis of Aging of Loans (Details) - USD ($) $ in Thousands	Mar. 31, 2025	Dec. 31, 2024
Gross loans	$ 8,206,343	$ 8,280,482
Nonaccrual	49,860	57,310
Financial Asset, 30 to 59 Days Past Due [Member]
Gross loans	14,829	3,331
Financial Asset, 60 to 89 Days Past Due [Member]
Gross loans	133	0
Financial Asset, Equal to or Greater than 90 Days Past Due [Member]
Gross loans	0	0
Financial Asset, Past Due [Member]
Gross loans	64,822	60,641
Financial Asset, Not Past Due [Member]
Gross loans	8,141,521	8,219,841
Commercial Portfolio Segment [Member]
Gross loans	1,492,920	1,532,730
Nonaccrual	16,181	16,231
Commercial Portfolio Segment [Member] \| Financial Asset, 30 to 59 Days Past Due [Member]
Gross loans	4,915	1,340
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	21,096	17,571
Commercial Portfolio Segment [Member] \| Financial Asset, Not Past Due [Member]
Gross loans	1,471,824	1,515,159
Commercial Real Estate Portfolio Segment [Member]
Gross loans	5,837,671	5,880,679
Nonaccrual	29,109	36,486
Commercial Real Estate Portfolio Segment [Member] \| Financial Asset, 30 to 59 Days Past Due [Member]
Gross loans	8,740	0
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	37,849	36,486
Commercial Real Estate Portfolio Segment [Member] \| Financial Asset, Not Past Due [Member]
Gross loans	5,799,822	5,844,193
Commercial Construction Portfolio Segment [Member]
Gross loans	617,593	616,246
Nonaccrual	2,204	2,204
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	0
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	2,204
Commercial Construction Portfolio Segment [Member] \| Financial Asset, Not Past Due [Member]
Gross loans	615,389	614,042
Residential Portfolio Segment [Member]
Gross loans	256,555	249,691
Nonaccrual	2,366	2,389
Residential Portfolio Segment [Member] \| Financial Asset, 30 to 59 Days Past Due [Member]
Gross loans	1,174	1,991
Residential Portfolio Segment [Member] \| Financial Asset, 60 to 89 Days Past Due [Member]
Gross loans	133	0
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	3,673	4,380
Residential Portfolio Segment [Member] \| Financial Asset, Not Past Due [Member]
Gross loans	252,882	245,311
Consumer Portfolio Segment [Member]
Gross loans	1,604	1,136
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	$ 1,604	$ 1,136