Note 8 - Loans - Portfolio by Risk Rating (Details) - USD ($) $ in Thousands	Jun. 30, 2019	Dec. 31, 2018
Loans	$ 14,593,510	$ 13,995,788
Commercial Portfolio Segment [Member]
Loans	2,772,982	2,741,965
Real Estate Construction Portfolio Segment [Member]
Loans	598,849	581,454
Commercial Real Estate Portfolio Segment [Member]
Loans	6,945,562	6,724,200
Residential Mortgage and Equity Lines Portfolio Segment [Member]
Loans	4,269,486	3,943,820
Consumer Portfolio Segment [Member]
Loans	6,631	4,349
Pass [Member]
Loans	14,006,992	13,394,786
Pass [Member] | Commercial Portfolio Segment [Member]
Loans	2,568,884	2,603,901
Pass [Member] | Real Estate Construction Portfolio Segment [Member]
Loans	538,843	514,406
Pass [Member] | Commercial Real Estate Portfolio Segment [Member]
Loans	6,632,331	6,337,368
Pass [Member] | Residential Mortgage and Equity Lines Portfolio Segment [Member]
Loans	4,260,303	3,934,762
Pass [Member] | Consumer Portfolio Segment [Member]
Loans	6,631	4,349
Special Mention [Member]
Loans	390,832	454,953
Special Mention [Member] | Commercial Portfolio Segment [Member]
Loans	111,658	87,987
Special Mention [Member] | Real Estate Construction Portfolio Segment [Member]
Loans	55,303	62,175
Special Mention [Member] | Commercial Real Estate Portfolio Segment [Member]
Loans	222,932	304,791
Special Mention [Member] | Residential Mortgage and Equity Lines Portfolio Segment [Member]
Loans	939	0
Special Mention [Member] | Consumer Portfolio Segment [Member]
Loans	0	0
Substandard [Member]
Loans	195,686	146,049
Substandard [Member] | Commercial Portfolio Segment [Member]
Loans	92,440	50,077
Substandard [Member] | Real Estate Construction Portfolio Segment [Member]
Loans	4,703	4,873
Substandard [Member] | Commercial Real Estate Portfolio Segment [Member]
Loans	90,299	82,041
Substandard [Member] | Residential Mortgage and Equity Lines Portfolio Segment [Member]
Loans	8,244	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