Note 8 - Loans - Portfolio by Risk Rating (Details) - USD ($) $ in Thousands	Sep. 30, 2018	Dec. 31, 2017
Loans	$ 13,647,646	$ 12,870,290
Loans held for sale		8,000
Commercial Portfolio Segment [Member]
Loans	2,674,089	2,461,266
Real Estate Construction Portfolio Segment [Member]
Loans	597,018	678,805
Commercial Real Estate Portfolio Segment [Member]
Loans	6,580,254	6,482,695
Residential Mortgage and Equity Lines Portfolio Segment [Member]
Loans	3,790,710	3,242,354
Consumer Portfolio Segment [Member]
Loans	5,575	5,170
Pass [Member]
Loans	12,995,238	12,140,143
Loans held for sale
Pass [Member] | Commercial Portfolio Segment [Member]
Loans	2,494,780	2,281,698
Pass [Member] | Real Estate Construction Portfolio Segment [Member]
Loans	531,579	616,411
Pass [Member] | Commercial Real Estate Portfolio Segment [Member]
Loans	6,181,227	6,004,258
Pass [Member] | Residential Mortgage and Equity Lines Portfolio Segment [Member]
Loans	3,782,077	3,232,606
Pass [Member] | Consumer Portfolio Segment [Member]
Loans	5,575	5,170
Special Mention [Member]
Loans	500,900	481,189
Loans held for sale
Special Mention [Member] | Commercial Portfolio Segment [Member]
Loans	125,373	118,056
Special Mention [Member] | Real Estate Construction Portfolio Segment [Member]
Loans	60,517	54,209
Special Mention [Member] | Commercial Real Estate Portfolio Segment [Member]
Loans	315,010	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	151,508	248,949
Loans held for sale		8,000
Substandard [Member] | Commercial Portfolio Segment [Member]
Loans	53,936	61,503
Substandard [Member] | Real Estate Construction Portfolio Segment [Member]
Loans	4,922	8,185
Substandard [Member] | Commercial Real Estate Portfolio Segment [Member]
Loans	84,017	169,513
Substandard [Member] | Residential Mortgage and Equity Lines Portfolio Segment [Member]
Loans	8,633	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