Note 4 - Loans and the Allowance for Credit Losses - Analysis of Aging of Loans (Details) - USD ($) $ in Thousands	Dec. 31, 2023	Dec. 31, 2022
Financing Receivable, before Allowance for Credit Loss, Fee and Loan in Process	$ 8,351,841	$ 8,109,161
Nonaccrual	52,524	44,454
Financial Asset, 30 to 59 Days Past Due [Member]
Financing Receivable, before Allowance for Credit Loss, Fee and Loan in Process	1,357	1,965
Financial Asset, 60 to 89 Days Past Due [Member]
Financing Receivable, before Allowance for Credit Loss, Fee and Loan in Process	23,826	0
Financial Asset, Equal to or Greater than 90 Days Past Due [Member]
Financing Receivable, before Allowance for Credit Loss, Fee and Loan in Process	0	5,591
Financial Asset, Past Due [Member]
Financing Receivable, before Allowance for Credit Loss, Fee and Loan in Process	77,707	52,010
Financial Asset, Not Past Due [Member]
Financing Receivable, before Allowance for Credit Loss, Fee and Loan in Process	8,274,134	8,057,151
Commercial Portfolio Segment [Member]
Financing Receivable, before Allowance for Credit Loss, Fee and Loan in Process	1,578,730	1,472,734
Nonaccrual	12,827	25,257
Commercial Portfolio Segment [Member] | Financial Asset, 30 to 59 Days Past Due [Member]
Financing Receivable, before Allowance for Credit Loss, Fee and Loan in Process	555	306
Commercial Portfolio Segment [Member] | Financial Asset, 60 to 89 Days Past Due [Member]
Financing Receivable, before Allowance for Credit Loss, Fee and Loan in Process	0	0
Commercial Portfolio Segment [Member] | Financial Asset, Equal to or Greater than 90 Days Past Due [Member]
Financing Receivable, before Allowance for Credit Loss, Fee and Loan in Process	0	0
Commercial Portfolio Segment [Member] | Financial Asset, Past Due [Member]
Financing Receivable, before Allowance for Credit Loss, Fee and Loan in Process	13,382	25,563
Commercial Portfolio Segment [Member] | Financial Asset, Not Past Due [Member]
Financing Receivable, before Allowance for Credit Loss, Fee and Loan in Process	1,565,348	1,447,171
Commercial Real Estate Portfolio Segment [Member]
Financing Receivable, before Allowance for Credit Loss, Fee and Loan in Process	5,895,545	5,795,228
Nonaccrual	36,192	16,817
Commercial Real Estate Portfolio Segment [Member] | Financial Asset, 30 to 59 Days Past Due [Member]
Financing Receivable, before Allowance for Credit Loss, Fee and Loan in Process	527	90
Commercial Real Estate Portfolio Segment [Member] | Financial Asset, 60 to 89 Days Past Due [Member]
Financing Receivable, before Allowance for Credit Loss, Fee and Loan in Process	0	0
Commercial Real Estate Portfolio Segment [Member] | Financial Asset, Equal to or Greater than 90 Days Past Due [Member]
Financing Receivable, before Allowance for Credit Loss, Fee and Loan in Process	0	5,591
Commercial Real Estate Portfolio Segment [Member] | Financial Asset, Past Due [Member]
Financing Receivable, before Allowance for Credit Loss, Fee and Loan in Process	36,719	22,498
Commercial Real Estate Portfolio Segment [Member] | Financial Asset, Not Past Due [Member]
Financing Receivable, before Allowance for Credit Loss, Fee and Loan in Process	5,858,826	5,772,730
Commercial Construction Portfolio Segment [Member]
Financing Receivable, before Allowance for Credit Loss, Fee and Loan in Process	620,496	574,139
Nonaccrual	0	0
Commercial Construction Portfolio Segment [Member] | Financial Asset, 30 to 59 Days Past Due [Member]
Financing Receivable, before Allowance for Credit Loss, Fee and Loan in Process	0	0
Commercial Construction Portfolio Segment [Member] | Financial Asset, 60 to 89 Days Past Due [Member]
Financing Receivable, before Allowance for Credit Loss, Fee and Loan in Process	23,600	0
Commercial Construction Portfolio Segment [Member] | Financial Asset, Equal to or Greater than 90 Days Past Due [Member]
Financing Receivable, before Allowance for Credit Loss, Fee and Loan in Process	0	0
Commercial Construction Portfolio Segment [Member] | Financial Asset, Past Due [Member]
Financing Receivable, before Allowance for Credit Loss, Fee and Loan in Process	23,600	0
Commercial Construction Portfolio Segment [Member] | Financial Asset, Not Past Due [Member]
Financing Receivable, before Allowance for Credit Loss, Fee and Loan in Process	596,896	574,139
Residential Portfolio Segment [Member]
Financing Receivable, before Allowance for Credit Loss, Fee and Loan in Process	256,041	264,748
Nonaccrual	3,505	2,380
Residential Portfolio Segment [Member] | Financial Asset, 30 to 59 Days Past Due [Member]
Financing Receivable, before Allowance for Credit Loss, Fee and Loan in Process	275	1,569
Residential Portfolio Segment [Member] | Financial Asset, 60 to 89 Days Past Due [Member]
Financing Receivable, before Allowance for Credit Loss, Fee and Loan in Process	226	0
Residential Portfolio Segment [Member] | Financial Asset, Equal to or Greater than 90 Days Past Due [Member]
Financing Receivable, before Allowance for Credit Loss, Fee and Loan in Process	0	0
Residential Portfolio Segment [Member] | Financial Asset, Past Due [Member]
Financing Receivable, before Allowance for Credit Loss, Fee and Loan in Process	4,006	3,949
Residential Portfolio Segment [Member] | Financial Asset, Not Past Due [Member]
Financing Receivable, before Allowance for Credit Loss, Fee and Loan in Process	252,035	260,799
Consumer Portfolio Segment [Member]
Financing Receivable, before Allowance for Credit Loss, Fee and Loan in Process	1,029	2,312
Nonaccrual	0	0
Consumer Portfolio Segment [Member] | Financial Asset, 30 to 59 Days Past Due [Member]
Financing Receivable, before Allowance for Credit Loss, Fee and Loan in Process	0	0
Consumer Portfolio Segment [Member] | Financial Asset, 60 to 89 Days Past Due [Member]
Financing Receivable, before Allowance for Credit Loss, Fee and Loan in Process	0	0
Consumer Portfolio Segment [Member] | Financial Asset, Equal to or Greater than 90 Days Past Due [Member]
Financing Receivable, before Allowance for Credit Loss, Fee and Loan in Process	0	0
Consumer Portfolio Segment [Member] | Financial Asset, Past Due [Member]
Financing Receivable, before Allowance for Credit Loss, Fee and Loan in Process	0	0
Consumer Portfolio Segment [Member] | Financial Asset, Not Past Due [Member]
Financing Receivable, before Allowance for Credit Loss, Fee and Loan in Process	$ 1,029	$ 2,312