Note 8 - Loans - Portfolio by Risk Rating (Details) - USD ($) $ in Thousands	Jun. 30, 2018	Dec. 31, 2017
Loans	$ 13,348,737	$ 12,870,290
Loans held for sale		8,000
Commercial Portfolio Segment [Member]
Loans	2,576,649	2,461,266
Real Estate Construction Portfolio Segment [Member]
Loans	581,917	678,805
Commercial Real Estate Portfolio Segment [Member]
Loans	6,615,791	6,482,695
Residential Mortgage and Equity Lines Portfolio Segment [Member]
Loans	3,570,320	3,242,354
Consumer Portfolio Segment [Member]
Loans	4,060	5,170
Pass [Member]
Loans	12,657,666	12,140,143
Loans held for sale
Pass [Member] | Commercial Portfolio Segment [Member]
Loans	2,374,736	2,281,698
Pass [Member] | Real Estate Construction Portfolio Segment [Member]
Loans	527,600	616,411
Pass [Member] | Commercial Real Estate Portfolio Segment [Member]
Loans	6,193,626	6,004,258
Pass [Member] | Residential Mortgage and Equity Lines Portfolio Segment [Member]
Loans	3,557,644	3,232,606
Pass [Member] | Consumer Portfolio Segment [Member]
Loans	4,060	5,170
Special Mention [Member]
Loans	476,589	481,189
Loans held for sale
Special Mention [Member] | Commercial Portfolio Segment [Member]
Loans	117,809	118,056
Special Mention [Member] | Real Estate Construction Portfolio Segment [Member]
Loans	46,277	54,209
Special Mention [Member] | Commercial Real Estate Portfolio Segment [Member]
Loans	312,503	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	214,482	248,949
Loans held for sale		8,000
Substandard [Member] | Commercial Portfolio Segment [Member]
Loans	84,104	61,503
Substandard [Member] | Real Estate Construction Portfolio Segment [Member]
Loans	8,040	8,185
Substandard [Member] | Commercial Real Estate Portfolio Segment [Member]
Loans	109,662	169,513
Substandard [Member] | Residential Mortgage and Equity Lines Portfolio Segment [Member]
Loans	12,676	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