Note 8 - Loans - Aging of Loan Portfolio (Details) - USD ($) $ in Thousands	Sep. 30, 2021	Dec. 31, 2020
Loans	$ 15,976,781	$ 15,644,396
Financial Asset, 30 to 59 Days Past Due [Member]
Loans	15,857	118,402
Financial Asset, 60 to 89 Days Past Due [Member]
Loans	4,777	25,474
Financial Asset, Equal to or Greater than 90 Days Past Due [Member]
Loans	4,333	4,982
Financial Asset, Past Due [Member]
Loans	93,649	216,542
Non-accrual loans	68,682	67,684
Financial Asset, Not Past Due [Member]
Loans	15,883,132	15,427,854
Commercial Portfolio Segment [Member]
Loans	2,871,693	2,836,833
Commercial Portfolio Segment [Member] | Financial Asset, 30 to 59 Days Past Due [Member]
Loans	15,391	52,601
Commercial Portfolio Segment [Member] | Financial Asset, 60 to 89 Days Past Due [Member]
Loans	2,326	3,182
Commercial Portfolio Segment [Member] | Financial Asset, Equal to or Greater than 90 Days Past Due [Member]
Loans	2,861	2,947
Commercial Portfolio Segment [Member] | Financial Asset, Past Due [Member]
Loans	37,676	81,817
Non-accrual loans	17,098	23,087
Commercial Portfolio Segment [Member] | Financial Asset, Not Past Due [Member]
Loans	2,834,017	2,755,016
Real Estate Construction Portfolio Segment [Member]
Loans	688,195	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	5,491	10,543
Non-accrual loans	5,491	4,286
Real Estate Construction Portfolio Segment [Member] | Financial Asset, Not Past Due [Member]
Loans	682,704	668,949
Commercial Real Estate Portfolio Segment [Member]
Loans	7,835,528	7,555,027
Commercial Real Estate Portfolio Segment [Member] | Financial Asset, 30 to 59 Days Past Due [Member]
Loans	458	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	1,472	2,035
Commercial Real Estate Portfolio Segment [Member] | Financial Asset, Past Due [Member]
Loans	38,898	99,005
Non-accrual loans	36,968	33,715
Commercial Real Estate Portfolio Segment [Member] | Financial Asset, Not Past Due [Member]
Loans	7,796,630	7,456,022
Residential Mortgage and Equity Lines Portfolio Segment [Member]
Loans	4,577,995	4,569,944
Residential Mortgage and Equity Lines Portfolio Segment [Member] | Financial Asset, 30 to 59 Days Past Due [Member]
Loans	0	14,315
Residential Mortgage and Equity Lines Portfolio Segment [Member] | Financial Asset, 60 to 89 Days Past Due [Member]
Loans	2,451	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	11,576	25,134
Non-accrual loans	9,125	6,596
Residential Mortgage and Equity Lines Portfolio Segment [Member] | Financial Asset, Not Past Due [Member]
Loans	4,566,419	4,544,810
Installment and Other Loans [Member ]
Loans	3,370	3,100
Installment and Other Loans [Member ] | Financial Asset, 30 to 59 Days Past Due [Member]
Loans	8	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	8	43
Non-accrual loans	0	0
Installment and Other Loans [Member ] | Financial Asset, Not Past Due [Member]
Loans	$ 3,362	$ 3,057