Note 5 - Loans - Portfolio by Risk Rating (Details) - USD ($) $ in Thousands	Dec. 31, 2018	Dec. 31, 2017
Loans	$ 13,995,788	$ 12,870,290
Loans held for sale		8,000
Commercial Portfolio Segment [Member]
Loans	2,741,965	2,461,266
Real Estate Construction Portfolio Segment [Member]
Loans	581,454	678,805
Commercial Real Estate Portfolio Segment [Member]
Loans	6,724,200	6,482,695
Residential Mortgage and Equity Lines Portfolio Segment [Member]
Loans	3,943,820	3,242,354
Consumer Portfolio Segment [Member]
Loans	4,349	5,170
Pass [Member]
Loans	13,394,786	12,140,143
Loans held for sale
Pass [Member] | Commercial Portfolio Segment [Member]
Loans	2,603,901	2,281,698
Pass [Member] | Real Estate Construction Portfolio Segment [Member]
Loans	514,406	616,411
Pass [Member] | Commercial Real Estate Portfolio Segment [Member]
Loans	6,337,368	6,004,258
Pass [Member] | Residential Mortgage and Equity Lines Portfolio Segment [Member]
Loans	3,934,762	3,232,606
Pass [Member] | Consumer Portfolio Segment [Member]
Loans	4,349	5,170
Special Mention [Member]
Loans	454,953	481,189
Loans held for sale
Special Mention [Member] | Commercial Portfolio Segment [Member]
Loans	87,987	118,056
Special Mention [Member] | Real Estate Construction Portfolio Segment [Member]
Loans	62,175	54,209
Special Mention [Member] | Commercial Real Estate Portfolio Segment [Member]
Loans	304,791	308,924
Special Mention [Member] | Residential Mortgage and Equity Lines Portfolio Segment [Member]
Loans
Special Mention [Member] | Consumer Portfolio Segment [Member]
Loans
Substandard [Member]
Loans	146,049	248,949
Loans held for sale		8,000
Substandard [Member] | Commercial Portfolio Segment [Member]
Loans	50,077	61,503
Substandard [Member] | Real Estate Construction Portfolio Segment [Member]
Loans	4,873	8,185
Substandard [Member] | Commercial Real Estate Portfolio Segment [Member]
Loans	82,041	169,513
Substandard [Member] | Residential Mortgage and Equity Lines Portfolio Segment [Member]
Loans	9,058	9,748
Substandard [Member] | Consumer Portfolio Segment [Member]
Loans
Doubtful [Member]
Loans		9
Loans held for sale
Doubtful [Member] | Commercial Portfolio Segment [Member]
Loans		9
Doubtful [Member] | Real Estate Construction Portfolio Segment [Member]
Loans
Doubtful [Member] | Commercial Real Estate Portfolio Segment [Member]
Loans
Doubtful [Member] | Residential Mortgage and Equity Lines Portfolio Segment [Member]
Loans
Doubtful [Member] | Consumer Portfolio Segment [Member]
Loans