Note 8 - Loans - Portfolio by Risk Rating (Details) - USD ($) $ in Thousands	Mar. 31, 2018	Dec. 31, 2017
Loans	$ 13,014,539	$ 12,870,290
Loans held for sale		8,000
Commercial Portfolio Segment [Member]
Loans	2,436,421	2,461,266
Real Estate Construction Portfolio Segment [Member]
Loans	587,927	678,805
Commercial Real Estate Portfolio Segment [Member]
Loans	6,610,254	6,482,695
Residential Mortgage and Equity Lines Portfolio Segment [Member]
Loans	3,375,464	3,242,354
Consumer Portfolio Segment [Member]
Loans	4,473	5,170
Pass [Member]
Loans	12,320,162	12,140,143
Loans held for sale
Pass [Member] | Commercial Portfolio Segment [Member]
Loans	2,224,463	2,281,698
Pass [Member] | Real Estate Construction Portfolio Segment [Member]
Loans	522,983	616,411
Pass [Member] | Commercial Real Estate Portfolio Segment [Member]
Loans	6,202,696	6,004,258
Pass [Member] | Residential Mortgage and Equity Lines Portfolio Segment [Member]
Loans	3,365,642	3,232,606
Pass [Member] | Consumer Portfolio Segment [Member]
Loans	4,378	5,170
Special Mention [Member]
Loans	488,543	481,189
Loans held for sale
Special Mention [Member] | Commercial Portfolio Segment [Member]
Loans	139,985	118,056
Special Mention [Member] | Real Estate Construction Portfolio Segment [Member]
Loans	55,911	54,209
Special Mention [Member] | Commercial Real Estate Portfolio Segment [Member]
Loans	292,647	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	205,834	248,949
Loans held for sale		8,000
Substandard [Member] | Commercial Portfolio Segment [Member]
Loans	71,973	61,503
Substandard [Member] | Real Estate Construction Portfolio Segment [Member]
Loans	9,033	8,185
Substandard [Member] | Commercial Real Estate Portfolio Segment [Member]
Loans	114,911	169,513
Substandard [Member] | Residential Mortgage and Equity Lines Portfolio Segment [Member]
Loans	9,822	9,748
Substandard [Member] | Consumer Portfolio Segment [Member]
Loans	95
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