Note 5 - Loans and the Allowance for Credit Losses - Analysis of Aging of Loans (Details) - USD ($) $ in Thousands	Sep. 30, 2023	Dec. 31, 2022
Gross loans	$ 8,188,210	$ 8,109,161
Nonaccrual	56,059	44,454
Financial Asset, 30 to 59 Days Past Due [Member]
Gross loans	660	1,965
Financial Asset, 60 to 89 Days Past Due [Member]
Gross loans	2,830	0
Financial Asset, Equal to or Greater than 90 Days Past Due [Member]
Gross loans	0	5,591
Financial Asset, Past Due [Member]
Gross loans	59,549	52,010
Financial Asset, Not Past Due [Member]
Gross loans	8,128,661	8,057,151
Commercial Portfolio Segment [Member]
Gross loans	1,475,571	1,472,734
Nonaccrual	22,159	25,257
Commercial Portfolio Segment [Member] | Financial Asset, 30 to 59 Days Past Due [Member]
Gross loans	433	306
Commercial Portfolio Segment [Member] | Financial Asset, 60 to 89 Days Past Due [Member]
Gross loans	1,979	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	24,571	25,563
Commercial Portfolio Segment [Member] | Financial Asset, Not Past Due [Member]
Gross loans	1,451,000	1,447,171
Commercial Real Estate Portfolio Segment [Member]
Gross loans	5,837,539	5,795,228
Nonaccrual	29,824	16,817
Commercial Real Estate Portfolio Segment [Member] | Financial Asset, 30 to 59 Days Past Due [Member]
Gross loans	0	90
Commercial Real Estate Portfolio Segment [Member] | Financial Asset, 60 to 89 Days Past Due [Member]
Gross loans	597	0
Commercial Real Estate Portfolio Segment [Member] | Financial Asset, Equal to or Greater than 90 Days Past Due [Member]
Gross loans	0	5,591
Commercial Real Estate Portfolio Segment [Member] | Financial Asset, Past Due [Member]
Gross loans	30,421	22,498
Commercial Real Estate Portfolio Segment [Member] | Financial Asset, Not Past Due [Member]
Gross loans	5,807,118	5,772,730
Commercial Construction Portfolio Segment [Member]
Gross loans	622,748	574,139
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	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	0	0
Commercial Construction Portfolio Segment [Member] | Financial Asset, Not Past Due [Member]
Gross loans	622,748	574,139
Residential Portfolio Segment [Member]
Gross loans	251,416	264,748
Nonaccrual	4,076	2,380
Residential Portfolio Segment [Member] | Financial Asset, 30 to 59 Days Past Due [Member]
Gross loans	227	1,569
Residential Portfolio Segment [Member] | Financial Asset, 60 to 89 Days Past Due [Member]
Gross loans	0	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	4,303	3,949
Residential Portfolio Segment [Member] | Financial Asset, Not Past Due [Member]
Gross loans	247,113	260,799
Consumer Portfolio Segment [Member]
Gross loans	936	2,312
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	254	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	254	0
Consumer Portfolio Segment [Member] | Financial Asset, Not Past Due [Member]
Gross loans	$ 682	$ 2,312