Note 5 - Loans - Portfolio by Risk Rating (Details) - USD ($) $ in Thousands	Dec. 31, 2017	Dec. 31, 2016
Loans	$ 12,870,290	$ 11,201,275
Loans held for sale	8,000	7,500
Commercial Portfolio Segment [Member]
Loans	2,461,266	2,248,187
Real Estate Construction Portfolio Segment [Member]
Loans	678,805	548,088
Commercial Real Estate Portfolio Segment [Member]
Loans	6,482,695	5,785,248
Residential Mortgage and Equity Lines Portfolio Segment [Member]
Loans	3,242,354	2,615,759
Consumer Portfolio Segment [Member]
Loans	5,170	3,993
Pass [Member]
Loans	12,140,143	10,513,473
Loans held for sale
Pass [Member] | Commercial Portfolio Segment [Member]
Loans	2,281,698	2,023,114
Pass [Member] | Real Estate Construction Portfolio Segment [Member]
Loans	616,411	469,909
Pass [Member] | Commercial Real Estate Portfolio Segment [Member]
Loans	6,004,258	5,410,623
Pass [Member] | Residential Mortgage and Equity Lines Portfolio Segment [Member]
Loans	3,232,606	2,605,834
Pass [Member] | Consumer Portfolio Segment [Member]
Loans	5,170	3,993
Special Mention [Member]
Loans	481,189	435,032
Loans held for sale
Special Mention [Member] | Commercial Portfolio Segment [Member]
Loans	118,056	140,682
Special Mention [Member] | Real Estate Construction Portfolio Segment [Member]
Loans	54,209	44,129
Special Mention [Member] | Commercial Real Estate Portfolio Segment [Member]
Loans	308,924	250,221
Special Mention [Member] | Residential Mortgage and Equity Lines Portfolio Segment [Member]
Loans
Special Mention [Member] | Consumer Portfolio Segment [Member]
Loans
Substandard [Member]
Loans	248,949	252,672
Loans held for sale	8,000	7,500
Substandard [Member] | Commercial Portfolio Segment [Member]
Loans	61,503	84,293
Substandard [Member] | Real Estate Construction Portfolio Segment [Member]
Loans	8,185	34,050
Substandard [Member] | Commercial Real Estate Portfolio Segment [Member]
Loans	169,513	124,404
Substandard [Member] | Residential Mortgage and Equity Lines Portfolio Segment [Member]
Loans	9,748	9,925
Substandard [Member] | Consumer Portfolio Segment [Member]
Loans
Doubtful [Member]
Loans	9	98
Loans held for sale
Doubtful [Member] | Commercial Portfolio Segment [Member]
Loans	9	98
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