Note 8 - Loans - Portfolio by Risk Rating (Details) - USD ($) $ in Thousands	Mar. 31, 2019	Dec. 31, 2018
Loans	$ 14,277,422	$ 13,995,788
Commercial Portfolio Segment [Member]
Loans	2,736,195	2,741,965
Real Estate Construction Portfolio Segment [Member]
Loans	567,789	581,454
Commercial Real Estate Portfolio Segment [Member]
Loans	6,888,898	6,724,200
Residential Mortgage and Equity Lines Portfolio Segment [Member]
Loans	4,076,907	3,943,820
Consumer Portfolio Segment [Member]
Loans	7,633	4,349
Pass [Member]
Loans	13,697,253	13,394,786
Pass [Member] | Commercial Portfolio Segment [Member]
Loans	2,547,294	2,603,901
Pass [Member] | Real Estate Construction Portfolio Segment [Member]
Loans	518,290	514,406
Pass [Member] | Commercial Real Estate Portfolio Segment [Member]
Loans	6,556,203	6,337,368
Pass [Member] | Residential Mortgage and Equity Lines Portfolio Segment [Member]
Loans	4,067,833	3,934,762
Pass [Member] | Consumer Portfolio Segment [Member]
Loans	7,633	4,349
Special Mention [Member]
Loans	409,251	454,953
Special Mention [Member] | Commercial Portfolio Segment [Member]
Loans	113,451	87,987
Special Mention [Member] | Real Estate Construction Portfolio Segment [Member]
Loans	44,699	62,175
Special Mention [Member] | Commercial Real Estate Portfolio Segment [Member]
Loans	250,331	304,791
Special Mention [Member] | Residential Mortgage and Equity Lines Portfolio Segment [Member]
Loans	770
Special Mention [Member] | Consumer Portfolio Segment [Member]
Loans
Substandard [Member]
Loans	170,918	146,049
Substandard [Member] | Commercial Portfolio Segment [Member]
Loans	75,450	50,077
Substandard [Member] | Real Estate Construction Portfolio Segment [Member]
Loans	4,800	4,873
Substandard [Member] | Commercial Real Estate Portfolio Segment [Member]
Loans	82,364	82,041
Substandard [Member] | Residential Mortgage and Equity Lines Portfolio Segment [Member]
Loans	8,304	9,058
Substandard [Member] | Consumer Portfolio Segment [Member]
Loans
Doubtful [Member]
Loans
Doubtful [Member] | Commercial Portfolio Segment [Member]
Loans
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