Note 9 - Loans - Aging of Loan Portfolio (Details) - USD ($) $ in Thousands	Sep. 30, 2023	Dec. 31, 2022
Loans	$ 19,023,822	$ 18,254,024
Non-accrual loans	77,330	68,854
Financial Asset, 30 to 59 Days Past Due [Member]
Loans	14,750	81,012
Financial Asset, 60 to 89 Days Past Due [Member]
Loans	20,672	8,921
Financial Asset, Equal to or Greater than 90 Days Past Due [Member]
Loans	1,924	11,580
Financial Asset, Past Due [Member]
Loans	114,676	170,367
Non-accrual loans	77,330	68,854
Financial Asset, Not Past Due [Member]
Loans	18,909,146	18,083,657
Commercial Portfolio Segment [Member]
Loans	3,090,609	3,318,778
Commercial Portfolio Segment [Member] \| Financial Asset, 30 to 59 Days Past Due [Member]
Loans	6,835	8,192
Commercial Portfolio Segment [Member] \| Financial Asset, 60 to 89 Days Past Due [Member]
Loans	3,634	3,235
Commercial Portfolio Segment [Member] \| Financial Asset, Equal to or Greater than 90 Days Past Due [Member]
Loans	1,204	10,208
Commercial Portfolio Segment [Member] \| Financial Asset, Past Due [Member]
Loans	26,334	47,407
Non-accrual loans	14,661	25,772
Commercial Portfolio Segment [Member] \| Financial Asset, Not Past Due [Member]
Loans	3,064,275	3,271,371
Real Estate Construction Portfolio Segment [Member]
Loans	474,294	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	16,992	0
Non-accrual loans	16,992	0
Real Estate Construction Portfolio Segment [Member] \| Financial Asset, Not Past Due [Member]
Loans	457,302	559,372
Commercial Real Estate Portfolio Segment [Member]
Loans	9,511,805	8,793,685
Commercial Real Estate Portfolio Segment [Member] \| Financial Asset, 30 to 59 Days Past Due [Member]
Loans	3,246	25,772
Commercial Real Estate Portfolio Segment [Member] \| Financial Asset, 60 to 89 Days Past Due [Member]
Loans	6,357	0
Commercial Real Estate Portfolio Segment [Member] \| Financial Asset, Equal to or Greater than 90 Days Past Due [Member]
Loans	720	1,372
Commercial Real Estate Portfolio Segment [Member] \| Financial Asset, Past Due [Member]
Loans	42,862	61,240
Non-accrual loans	32,539	34,096
Commercial Real Estate Portfolio Segment [Member] \| Financial Asset, Not Past Due [Member]
Loans	9,468,943	8,732,445
Residential Mortgage and Equity Lines Portfolio Segment [Member]
Loans	5,939,670	5,577,500
Residential Mortgage and Equity Lines Portfolio Segment [Member] \| Financial Asset, 30 to 59 Days Past Due [Member]
Loans	4,663	47,043
Residential Mortgage and Equity Lines Portfolio Segment [Member] \| Financial Asset, 60 to 89 Days Past Due [Member]
Loans	10,681	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	28,482	61,706
Non-accrual loans	13,138	8,978
Residential Mortgage and Equity Lines Portfolio Segment [Member] \| Financial Asset, Not Past Due [Member]
Loans	5,911,188	5,515,794
Installment and Other Loans [Member ]
Loans	7,444	4,689
Installment and Other Loans [Member ] \| Financial Asset, 30 to 59 Days Past Due [Member]
Loans	6	5
Installment and Other Loans [Member ] \| Financial Asset, 60 to 89 Days Past Due [Member]
Loans	0	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	6	14
Non-accrual loans	0	8
Installment and Other Loans [Member ] \| Financial Asset, Not Past Due [Member]
Loans	$ 7,438	$ 4,675