Note 9 - Loans - Aging of Loan Portfolio (Details) - USD ($) $ in Thousands	Jun. 30, 2023	Dec. 31, 2022
Loans	$ 18,952,794	$ 18,254,024
Non-accrual loans	69,004	68,854
Financial Asset, 30 to 59 Days Past Due [Member]
Loans	14,467	81,012
Financial Asset, 60 to 89 Days Past Due [Member]
Loans	12,535	8,921
Financial Asset, Equal to or Greater than 90 Days Past Due [Member]
Loans	5,968	11,580
Financial Asset, Past Due [Member]
Loans	101,974	170,367
Non-accrual loans	69,004	68,854
Financial Asset, Not Past Due [Member]
Loans	18,850,820	18,083,657
Commercial Portfolio Segment [Member]
Loans	3,317,868	3,318,778
Commercial Portfolio Segment [Member] | Financial Asset, 30 to 59 Days Past Due [Member]
Loans	1,767	8,192
Commercial Portfolio Segment [Member] | Financial Asset, 60 to 89 Days Past Due [Member]
Loans	1,033	3,235
Commercial Portfolio Segment [Member] | Financial Asset, Equal to or Greater than 90 Days Past Due [Member]
Loans	194	10,208
Commercial Portfolio Segment [Member] | Financial Asset, Past Due [Member]
Loans	20,568	47,407
Non-accrual loans	17,574	25,772
Commercial Portfolio Segment [Member] | Financial Asset, Not Past Due [Member]
Loans	3,297,300	3,271,371
Real Estate Construction Portfolio Segment [Member]
Loans	521,673	559,372
Real Estate Construction Portfolio Segment [Member] | Financial Asset, 30 to 59 Days Past Due [Member]
Loans	9,255	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	9,255	0
Non-accrual loans	0	0
Real Estate Construction Portfolio Segment [Member] | Financial Asset, Not Past Due [Member]
Loans	512,418	559,372
Commercial Real Estate Portfolio Segment [Member]
Loans	9,293,475	8,793,685
Commercial Real Estate Portfolio Segment [Member] | Financial Asset, 30 to 59 Days Past Due [Member]
Loans	1,591	25,772
Commercial Real Estate Portfolio Segment [Member] | Financial Asset, 60 to 89 Days Past Due [Member]
Loans	3,793	0
Commercial Real Estate Portfolio Segment [Member] | Financial Asset, Equal to or Greater than 90 Days Past Due [Member]
Loans	5,774	1,372
Commercial Real Estate Portfolio Segment [Member] | Financial Asset, Past Due [Member]
Loans	50,716	61,240
Non-accrual loans	39,558	34,096
Commercial Real Estate Portfolio Segment [Member] | Financial Asset, Not Past Due [Member]
Loans	9,242,759	8,732,445
Residential Mortgage and Equity Lines Portfolio Segment [Member]
Loans	5,814,521	5,577,500
Residential Mortgage and Equity Lines Portfolio Segment [Member] | Financial Asset, 30 to 59 Days Past Due [Member]
Loans	1,854	47,043
Residential Mortgage and Equity Lines Portfolio Segment [Member] | Financial Asset, 60 to 89 Days Past Due [Member]
Loans	7,701	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	21,427	61,706
Non-accrual loans	11,872	8,978
Residential Mortgage and Equity Lines Portfolio Segment [Member] | Financial Asset, Not Past Due [Member]
Loans	5,793,094	5,515,794
Installment and Other Loans [Member ]
Loans	5,257	4,689
Installment and Other Loans [Member ] | Financial Asset, 30 to 59 Days Past Due [Member]
Loans	0	5
Installment and Other Loans [Member ] | Financial Asset, 60 to 89 Days Past Due [Member]
Loans	8	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	8	14
Non-accrual loans	0	8
Installment and Other Loans [Member ] | Financial Asset, Not Past Due [Member]
Loans	$ 5,249	$ 4,675