Note 5 - Loans and the Allowance for Credit Losses - Analysis of Aging of Loans (Details) - USD ($) $ in Thousands	Jun. 30, 2023	Dec. 31, 2022
Gross loans	$ 8,156,217	$ 8,109,161
Nonaccrual	51,496	44,454
Financial Asset, 30 to 59 Days Past Due [Member]
Gross loans	508	1,965
Financial Asset, 60 to 89 Days Past Due [Member]
Gross loans	2,347	0
Financial Asset, Equal to or Greater than 90 Days Past Due [Member]
Gross loans	5,739	5,591
Financial Asset, Past Due [Member]
Gross loans	60,090	52,010
Financial Asset, Not Past Due [Member]
Gross loans	8,096,127	8,057,151
Commercial Portfolio Segment [Member]
Gross loans	1,472,795	1,472,734
Nonaccrual	24,653	25,257
Commercial Portfolio Segment [Member] | Financial Asset, 30 to 59 Days Past Due [Member]
Gross loans	457	306
Commercial Portfolio Segment [Member] | Financial Asset, 60 to 89 Days Past Due [Member]
Gross loans	1,375	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	26,485	25,563
Commercial Portfolio Segment [Member] | Financial Asset, Not Past Due [Member]
Gross loans	1,446,310	1,447,171
Commercial Real Estate Portfolio Segment [Member]
Gross loans	5,831,382	5,795,228
Nonaccrual	23,529	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	534	0
Commercial Real Estate Portfolio Segment [Member] | Financial Asset, Equal to or Greater than 90 Days Past Due [Member]
Gross loans	5,739	5,591
Commercial Real Estate Portfolio Segment [Member] | Financial Asset, Past Due [Member]
Gross loans	29,802	22,498
Commercial Real Estate Portfolio Segment [Member] | Financial Asset, Not Past Due [Member]
Gross loans	5,801,580	5,772,730
Commercial Construction Portfolio Segment [Member]
Gross loans	596,219	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	596,219	574,139
Residential Portfolio Segment [Member]
Gross loans	254,405	264,748
Nonaccrual	3,314	2,380
Residential Portfolio Segment [Member] | Financial Asset, 30 to 59 Days Past Due [Member]
Gross loans	51	1,569
Residential Portfolio Segment [Member] | Financial Asset, 60 to 89 Days Past Due [Member]
Gross loans	438	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	3,803	3,949
Residential Portfolio Segment [Member] | Financial Asset, Not Past Due [Member]
Gross loans	250,602	260,799
Consumer Portfolio Segment [Member]
Gross loans	1,416	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	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	$ 1,416	$ 2,312