Note 4 - Loans - Aging of Loan Portfolio (Details) - USD ($) $ in Thousands	Dec. 31, 2021	Dec. 31, 2020
Loans	$ 16,342,479	$ 15,644,396
Financial Asset, 30 to 59 Days Past Due [Member]
Loans	32,812	118,402
Financial Asset, 60 to 89 Days Past Due [Member]
Loans	13,015	25,474
Financial Asset, Equal to or Greater than 90 Days Past Due [Member]
Loans	1,439	4,982
Financial Asset, Past Due [Member]
Loans	113,112	216,542
Non-accrual loans	65,846	67,684
Financial Asset, Not Past Due [Member]
Loans	16,229,367	15,427,854
Commercial Portfolio Segment [Member]
Loans	2,982,399	2,836,833
Commercial Portfolio Segment [Member] | Financial Asset, 30 to 59 Days Past Due [Member]
Loans	4,294	52,601
Commercial Portfolio Segment [Member] | Financial Asset, 60 to 89 Days Past Due [Member]
Loans	9,877	3,182
Commercial Portfolio Segment [Member] | Financial Asset, Equal to or Greater than 90 Days Past Due [Member]
Loans	1,439	2,947
Commercial Portfolio Segment [Member] | Financial Asset, Past Due [Member]
Loans	32,168	81,817
Non-accrual loans	16,558	23,087
Commercial Portfolio Segment [Member] | Financial Asset, Not Past Due [Member]
Loans	2,950,231	2,755,016
Real Estate Construction Portfolio Segment [Member]
Loans	611,031	679,492
Real Estate Construction Portfolio Segment [Member] | Financial Asset, 30 to 59 Days Past Due [Member]
Loans	0	6,257
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	10,543
Non-accrual loans	0	4,286
Real Estate Construction Portfolio Segment [Member] | Financial Asset, Not Past Due [Member]
Loans	611,031	668,949
Commercial Real Estate Portfolio Segment [Member]
Loans	8,143,272	7,555,027
Commercial Real Estate Portfolio Segment [Member] | Financial Asset, 30 to 59 Days Past Due [Member]
Loans	8,389	45,186
Commercial Real Estate Portfolio Segment [Member] | Financial Asset, 60 to 89 Days Past Due [Member]
Loans	0	18,069
Commercial Real Estate Portfolio Segment [Member] | Financial Asset, Equal to or Greater than 90 Days Past Due [Member]
Loans	0	2,035
Commercial Real Estate Portfolio Segment [Member] | Financial Asset, Past Due [Member]
Loans	46,562	99,005
Non-accrual loans	38,173	33,715
Commercial Real Estate Portfolio Segment [Member] | Financial Asset, Not Past Due [Member]
Loans	8,096,710	7,456,022
Residential Mortgage and Equity Lines Portfolio Segment [Member]
Loans	4,601,493	4,569,944
Residential Mortgage and Equity Lines Portfolio Segment [Member] | Financial Asset, 30 to 59 Days Past Due [Member]
Loans	20,129	14,315
Residential Mortgage and Equity Lines Portfolio Segment [Member] | Financial Asset, 60 to 89 Days Past Due [Member]
Loans	3,138	4,223
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	34,382	25,134
Non-accrual loans	11,115	6,596
Residential Mortgage and Equity Lines Portfolio Segment [Member] | Financial Asset, Not Past Due [Member]
Loans	4,567,111	4,544,810
Installment and Other Loans [Member ]
Loans	4,284	3,100
Installment and Other Loans [Member ] | Financial Asset, 30 to 59 Days Past Due [Member]
Loans	0	43
Installment and Other Loans [Member ] | Financial Asset, 60 to 89 Days Past Due [Member]
Loans	0	0
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	0	43
Non-accrual loans	0	0
Installment and Other Loans [Member ] | Financial Asset, Not Past Due [Member]
Loans	$ 4,284	$ 3,057