Note 8 - Loans - Portfolio by Risk Rating (Details) - USD ($) $ in Thousands	Jun. 30, 2021	Dec. 31, 2020
Loans	$ 15,690,689	$ 15,644,396
Commercial Portfolio Segment [Member]
Loans	2,867,437	2,836,833
Real Estate Construction Portfolio Segment [Member]
Loans	664,495	679,492
Commercial Real Estate Portfolio Segment [Member]
Loans	7,615,088	7,555,027
Residential Mortgage and Equity Lines Portfolio Segment [Member]
Loans	4,540,537	4,569,944
Installment and Other Loans [Member ]
Loans	$ 3,132	3,100
Pass [Member]
Loans		14,927,044
Pass [Member] | Commercial Portfolio Segment [Member]
Loans		2,581,128
Pass [Member] | Real Estate Construction Portfolio Segment [Member]
Loans		593,196
Pass [Member] | Commercial Real Estate Portfolio Segment [Member]
Loans		7,202,568
Pass [Member] | Residential Mortgage and Equity Lines Portfolio Segment [Member]
Loans		4,547,052
Pass [Member] | Installment and Other Loans [Member ]
Loans		3,100
Special Mention [Member]
Loans		421,284
Special Mention [Member] | Commercial Portfolio Segment [Member]
Loans		141,344
Special Mention [Member] | Real Estate Construction Portfolio Segment [Member]
Loans		82,010
Special Mention [Member] | Commercial Real Estate Portfolio Segment [Member]
Loans		186,283
Special Mention [Member] | Residential Mortgage and Equity Lines Portfolio Segment [Member]
Loans		11,647
Special Mention [Member] | Installment and Other Loans [Member ]
Loans		0
Substandard [Member]
Loans		290,495
Substandard [Member] | Commercial Portfolio Segment [Member]
Loans		108,788
Substandard [Member] | Real Estate Construction Portfolio Segment [Member]
Loans		4,286
Substandard [Member] | Commercial Real Estate Portfolio Segment [Member]
Loans		166,176
Substandard [Member] | Residential Mortgage and Equity Lines Portfolio Segment [Member]
Loans		11,245
Substandard [Member] | Installment and Other Loans [Member ]
Loans		0
Doubtful [Member]
Loans		5,573
Doubtful [Member] | Commercial Portfolio Segment [Member]
Loans		5,573
Doubtful [Member] | Real Estate Construction Portfolio Segment [Member]
Loans		0
Doubtful [Member] | Commercial Real Estate Portfolio Segment [Member]
Loans		0
Doubtful [Member] | Residential Mortgage and Equity Lines Portfolio Segment [Member]
Loans		0
Doubtful [Member] | Installment and Other Loans [Member ]
Loans		$ 0