Note 8 - Loans - Portfolio by Risk Rating (Details) - USD ($) $ in Thousands	Sep. 30, 2019	Dec. 31, 2018
Loans	$ 14,728,554	$ 13,995,788
Commercial Portfolio Segment [Member]
Loans	2,668,061	2,741,965
Real Estate Construction Portfolio Segment [Member]
Loans	593,816	581,454
Commercial Real Estate Portfolio Segment [Member]
Loans	7,135,599	6,724,200
Residential Mortgage and Equity Lines Portfolio Segment [Member]
Loans	4,325,991	3,943,820
Consumer Portfolio Segment [Member]
Loans	5,087	4,349
Pass [Member]
Loans	14,094,469	13,394,786
Pass [Member] | Commercial Portfolio Segment [Member]
Loans	2,432,623	2,603,901
Pass [Member] | Real Estate Construction Portfolio Segment [Member]
Loans	514,725	514,406
Pass [Member] | Commercial Real Estate Portfolio Segment [Member]
Loans	6,824,241	6,337,368
Pass [Member] | Residential Mortgage and Equity Lines Portfolio Segment [Member]
Loans	4,317,793	3,934,762
Pass [Member] | Consumer Portfolio Segment [Member]
Loans	5,087	4,349
Special Mention [Member]
Loans	459,809	454,953
Special Mention [Member] | Commercial Portfolio Segment [Member]
Loans	151,265	87,987
Special Mention [Member] | Real Estate Construction Portfolio Segment [Member]
Loans	74,462	62,175
Special Mention [Member] | Commercial Real Estate Portfolio Segment [Member]
Loans	233,155	304,791
Special Mention [Member] | Residential Mortgage and Equity Lines Portfolio Segment [Member]
Loans	927	0
Special Mention [Member] | Consumer Portfolio Segment [Member]
Loans	0	0
Substandard [Member]
Loans	174,276	146,049
Substandard [Member] | Commercial Portfolio Segment [Member]
Loans	84,173	50,077
Substandard [Member] | Real Estate Construction Portfolio Segment [Member]
Loans	4,629	4,873
Substandard [Member] | Commercial Real Estate Portfolio Segment [Member]
Loans	78,203	82,041
Substandard [Member] | Residential Mortgage and Equity Lines Portfolio Segment [Member]
Loans	7,271	9,058
Substandard [Member] | Consumer Portfolio Segment [Member]
Loans	0	0
Doubtful [Member]
Loans	0	0
Doubtful [Member] | Commercial Portfolio Segment [Member]
Loans	0	0
Doubtful [Member] | Real Estate Construction Portfolio Segment [Member]
Loans	0	0
Doubtful [Member] | Commercial Real Estate Portfolio Segment [Member]
Loans	0	0
Doubtful [Member] | Residential Mortgage and Equity Lines Portfolio Segment [Member]
Loans	0	0
Doubtful [Member] | Consumer Portfolio Segment [Member]
Loans	$ 0	$ 0