Note 5 - Loans and the Allowance for Credit Losses - Analysis of Aging of Loans (Details) - USD ($) $ in Thousands	Mar. 31, 2023	Dec. 31, 2022
Gross loans	$ 8,141,176	$ 8,109,161
Nonaccrual	47,667	44,454
Financial Asset, 30 to 59 Days Past Due [Member]
Gross loans	13,079	1,965
Financial Asset, 60 to 89 Days Past Due [Member]
Gross loans	810	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	61,556	52,010
Financial Asset, Not Past Due [Member]
Gross loans	8,079,620	8,057,151
Commercial Portfolio Segment [Member]
Gross loans	1,414,226	1,472,734
Nonaccrual	19,321	25,257
Commercial Portfolio Segment [Member] | Financial Asset, 30 to 59 Days Past Due [Member]
Gross loans	1,929	306
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	21,250	25,563
Commercial Portfolio Segment [Member] | Financial Asset, Not Past Due [Member]
Gross loans	1,392,976	1,447,171
Commercial Real Estate Portfolio Segment [Member]
Gross loans	5,835,880	5,795,228
Nonaccrual	25,486	16,817
Commercial Real Estate Portfolio Segment [Member] | Financial Asset, 30 to 59 Days Past Due [Member]
Gross loans	5,740	90
Commercial Real Estate Portfolio Segment [Member] | Financial Asset, 60 to 89 Days Past Due [Member]
Gross loans	810	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	32,036	22,498
Commercial Real Estate Portfolio Segment [Member] | Financial Asset, Not Past Due [Member]
Gross loans	5,803,844	5,772,730
Commercial Construction Portfolio Segment [Member]
Gross loans	630,469	574,139
Nonaccrual	0	0
Commercial Construction Portfolio Segment [Member] | Financial Asset, 30 to 59 Days Past Due [Member]
Gross loans	4,707	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	4,707	0
Commercial Construction Portfolio Segment [Member] | Financial Asset, Not Past Due [Member]
Gross loans	625,762	574,139
Residential Portfolio Segment [Member]
Gross loans	259,166	264,748
Nonaccrual	2,860	2,380
Residential Portfolio Segment [Member] | Financial Asset, 30 to 59 Days Past Due [Member]
Gross loans	703	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	3,563	3,949
Residential Portfolio Segment [Member] | Financial Asset, Not Past Due [Member]
Gross loans	255,603	260,799
Consumer Portfolio Segment [Member]
Gross loans	1,435	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	$ 1,435	$ 2,312