Note 4 - Loans - Portfolio by Risk Rating (Details) - USD ($) $ in Thousands	Dec. 31, 2019	Dec. 31, 2018
Loans	$ 15,075,481	$ 13,995,788
Commercial Portfolio Segment [Member]
Loans	2,778,744	2,741,965
Real Estate Construction Portfolio Segment [Member]
Loans	579,864	581,454
Commercial Real Estate Portfolio Segment [Member]
Loans	7,275,262	6,724,200
Residential Mortgage and Equity Lines Portfolio Segment [Member]
Loans	4,436,561	3,943,820
Consumer Portfolio Segment [Member]
Loans	5,050	4,349
Pass [Member]
Loans	14,415,729	13,394,786
Pass [Member] | Commercial Portfolio Segment [Member]
Loans	2,528,944	2,603,901
Pass [Member] | Real Estate Construction Portfolio Segment [Member]
Loans	461,597	514,406
Pass [Member] | Commercial Real Estate Portfolio Segment [Member]
Loans	6,992,933	6,337,368
Pass [Member] | Residential Mortgage and Equity Lines Portfolio Segment [Member]
Loans	4,427,205	3,934,762
Pass [Member] | Consumer Portfolio Segment [Member]
Loans	5,050	4,349
Special Mention [Member]
Loans	477,071	454,953
Special Mention [Member] | Commercial Portfolio Segment [Member]
Loans	166,016	87,987
Special Mention [Member] | Real Estate Construction Portfolio Segment [Member]
Loans	113,687	62,175
Special Mention [Member] | Commercial Real Estate Portfolio Segment [Member]
Loans	196,454	304,791
Special Mention [Member] | Residential Mortgage and Equity Lines Portfolio Segment [Member]
Loans	914	0
Special Mention [Member] | Consumer Portfolio Segment [Member]
Loans	0	0
Substandard [Member]
Loans	182,681	146,049
Substandard [Member] | Commercial Portfolio Segment [Member]
Loans	83,784	50,077
Substandard [Member] | Real Estate Construction Portfolio Segment [Member]
Loans	4,580	4,873
Substandard [Member] | Commercial Real Estate Portfolio Segment [Member]
Loans	85,875	82,041
Substandard [Member] | Residential Mortgage and Equity Lines Portfolio Segment [Member]
Loans	8,442	9,058
Substandard [Member] | Consumer Portfolio Segment [Member]
Loans	0	0
Doubtful [Member]
Loans	0	0
Doubtful [Member] | Commercial Portfolio Segment [Member]
Loans	0	0
Doubtful [Member] | Real Estate Construction Portfolio Segment [Member]
Loans	0	0
Doubtful [Member] | Commercial Real Estate Portfolio Segment [Member]
Loans	0	0
Doubtful [Member] | Residential Mortgage and Equity Lines Portfolio Segment [Member]
Loans	0	0
Doubtful [Member] | Consumer Portfolio Segment [Member]
Loans	$ 0	$ 0