Note 9 - Loans - Aging of Loan Portfolio (Details) - USD ($) $ in Thousands	Mar. 31, 2023	Dec. 31, 2022
Loans	$ 18,317,339	$ 18,254,024
Financial Asset, 30 to 59 Days Past Due [Member]
Loans	59,500	81,012
Financial Asset, 60 to 89 Days Past Due [Member]
Loans	282	8,921
Financial Asset, Equal to or Greater than 90 Days Past Due [Member]
Loans	12,756	11,580
Financial Asset, Past Due [Member]
Loans	146,118	170,367
Non-accrual loans	73,580	68,854
Financial Asset, Not Past Due [Member]
Loans	18,171,221	18,083,657
Commercial Portfolio Segment [Member]
Loans	3,153,039	3,318,778
Commercial Portfolio Segment [Member] | Financial Asset, 30 to 59 Days Past Due [Member]
Loans	7,623	8,192
Commercial Portfolio Segment [Member] | Financial Asset, 60 to 89 Days Past Due [Member]
Loans	272	3,235
Commercial Portfolio Segment [Member] | Financial Asset, Equal to or Greater than 90 Days Past Due [Member]
Loans	100	10,208
Commercial Portfolio Segment [Member] | Financial Asset, Past Due [Member]
Loans	30,074	47,407
Non-accrual loans	22,079	25,772
Commercial Portfolio Segment [Member] | Financial Asset, Not Past Due [Member]
Loans	3,122,965	3,271,371
Real Estate Construction Portfolio Segment [Member]
Loans	558,967	559,372
Real Estate Construction Portfolio Segment [Member] | Financial Asset, 30 to 59 Days Past Due [Member]
Loans	0	0
Real Estate Construction Portfolio Segment [Member] | Financial Asset, 60 to 89 Days Past Due [Member]
Loans	0	0
Real Estate Construction Portfolio Segment [Member] | Financial Asset, Equal to or Greater than 90 Days Past Due [Member]
Loans	0	0
Real Estate Construction Portfolio Segment [Member] | Financial Asset, Past Due [Member]
Loans	0	0
Non-accrual loans	0	0
Real Estate Construction Portfolio Segment [Member] | Financial Asset, Not Past Due [Member]
Loans	558,967	559,372
Commercial Real Estate Portfolio Segment [Member]
Loans	8,916,766	8,793,685
Commercial Real Estate Portfolio Segment [Member] | Financial Asset, 30 to 59 Days Past Due [Member]
Loans	19,870	25,772
Commercial Real Estate Portfolio Segment [Member] | Financial Asset, 60 to 89 Days Past Due [Member]
Loans	0	0
Commercial Real Estate Portfolio Segment [Member] | Financial Asset, Equal to or Greater than 90 Days Past Due [Member]
Loans	12,656	1,372
Commercial Real Estate Portfolio Segment [Member] | Financial Asset, Past Due [Member]
Loans	72,744	61,240
Non-accrual loans	40,218	34,096
Commercial Real Estate Portfolio Segment [Member] | Financial Asset, Not Past Due [Member]
Loans	8,844,022	8,732,445
Residential Mortgage and Equity Lines Portfolio Segment [Member]
Loans	5,682,850	5,577,500
Residential Mortgage and Equity Lines Portfolio Segment [Member] | Financial Asset, 30 to 59 Days Past Due [Member]
Loans	31,998	47,043
Residential Mortgage and Equity Lines Portfolio Segment [Member] | Financial Asset, 60 to 89 Days Past Due [Member]
Loans	0	5,685
Residential Mortgage and Equity Lines Portfolio Segment [Member] | Financial Asset, Equal to or Greater than 90 Days Past Due [Member]
Loans	0	0
Residential Mortgage and Equity Lines Portfolio Segment [Member] | Financial Asset, Past Due [Member]
Loans	43,281	61,706
Non-accrual loans	11,283	8,978
Residential Mortgage and Equity Lines Portfolio Segment [Member] | Financial Asset, Not Past Due [Member]
Loans	5,639,569	5,515,794
Installment and Other Loans [Member ]
Loans	5,717	4,689
Installment and Other Loans [Member ] | Financial Asset, 30 to 59 Days Past Due [Member]
Loans	9	5
Installment and Other Loans [Member ] | Financial Asset, 60 to 89 Days Past Due [Member]
Loans	10	1
Installment and Other Loans [Member ] | Financial Asset, Equal to or Greater than 90 Days Past Due [Member]
Loans	0	0
Installment and Other Loans [Member ] | Financial Asset, Past Due [Member]
Loans	19	14
Non-accrual loans	0	8
Installment and Other Loans [Member ] | Financial Asset, Not Past Due [Member]
Loans	$ 5,698	$ 4,675