Note 8 - Loans - Portfolio by Risk Rating (Details) - USD ($) $ in Thousands	Jun. 30, 2020	Dec. 31, 2019
Loans	$ 15,608,283	$ 15,075,481
Commercial Portfolio Segment [Member]
Loans	3,007,966	2,778,744
Real Estate Construction Portfolio Segment [Member]
Loans	624,199	579,864
Commercial Real Estate Portfolio Segment [Member]
Loans	7,391,502	7,275,262
Residential Mortgage and Equity Lines Portfolio Segment [Member]
Loans	4,583,928	4,436,561
Consumer Portfolio Segment [Member]
Loans	688	5,050
Pass [Member]
Loans	14,965,924	14,415,729
Pass [Member] | Commercial Portfolio Segment [Member]
Loans	2,760,857	2,528,944
Pass [Member] | Real Estate Construction Portfolio Segment [Member]
Loans	490,388	461,597
Pass [Member] | Commercial Real Estate Portfolio Segment [Member]
Loans	7,155,796	6,992,933
Pass [Member] | Residential Mortgage and Equity Lines Portfolio Segment [Member]
Loans	4,558,199	4,427,205
Pass [Member] | Consumer Portfolio Segment [Member]
Loans	684	5,050
Special Mention [Member]
Loans	413,580	477,071
Special Mention [Member] | Commercial Portfolio Segment [Member]
Loans	138,410	166,016
Special Mention [Member] | Real Estate Construction Portfolio Segment [Member]
Loans	129,378	113,687
Special Mention [Member] | Commercial Real Estate Portfolio Segment [Member]
Loans	144,903	196,454
Special Mention [Member] | Residential Mortgage and Equity Lines Portfolio Segment [Member]
Loans	889	914
Special Mention [Member] | Consumer Portfolio Segment [Member]
Loans	0	0
Substandard [Member]
Loans	228,779	182,681
Substandard [Member] | Commercial Portfolio Segment [Member]
Loans	108,699	83,784
Substandard [Member] | Real Estate Construction Portfolio Segment [Member]
Loans	4,433	4,580
Substandard [Member] | Commercial Real Estate Portfolio Segment [Member]
Loans	90,803	85,875
Substandard [Member] | Residential Mortgage and Equity Lines Portfolio Segment [Member]
Loans	24,840	8,442
Substandard [Member] | Consumer Portfolio Segment [Member]
Loans	4	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