Note 8 - Loans - Aging of Loan Portfolio (Details) - USD ($) $ in Thousands	Jun. 30, 2019	Dec. 31, 2018
Loans past due	$ 87,717	$ 106,057
Non-accrual loans	54,748	41,815
Loans not past due	14,505,793	13,889,731
Loans	14,593,510	13,995,788
Financial Asset, 30 to 59 Days Past Due [Member]
Loans past due	12,755	45,978
Financial Asset, 60 to 89 Days Past Due [Member]
Loans past due	5,745	14,491
Financial Asset, Equal to or Greater than 90 Days Past Due [Member]
Loans past due	14,469	3,773
Commercial Portfolio Segment [Member]
Loans past due	34,038	47,267
Non-accrual loans	28,070	18,805
Loans not past due	2,738,944	2,694,698
Loans	2,772,982	2,741,965
Commercial Portfolio Segment [Member] | Financial Asset, 30 to 59 Days Past Due [Member]
Loans past due	4,998	25,494
Commercial Portfolio Segment [Member] | Financial Asset, 60 to 89 Days Past Due [Member]
Loans past due	970	2,454
Commercial Portfolio Segment [Member] | Financial Asset, Equal to or Greater than 90 Days Past Due [Member]
Loans past due	0	514
Real Estate Construction Portfolio Segment [Member]
Loans past due	7,529	8,028
Non-accrual loans	4,702	4,872
Loans not past due	591,320	573,426
Loans	598,849	581,454
Real Estate Construction Portfolio Segment [Member] | Financial Asset, 30 to 59 Days Past Due [Member]
Loans past due	2,827	0
Real Estate Construction Portfolio Segment [Member] | Financial Asset, 60 to 89 Days Past Due [Member]
Loans past due	0	3,156
Real Estate Construction Portfolio Segment [Member] | Financial Asset, Equal to or Greater than 90 Days Past Due [Member]
Loans past due	0	0
Commercial Real Estate Portfolio Segment [Member]
Loans past due	38,178	33,212
Non-accrual loans	14,515	10,611
Loans not past due	6,907,384	6,690,988
Loans	6,945,562	6,724,200
Commercial Real Estate Portfolio Segment [Member] | Financial Asset, 30 to 59 Days Past Due [Member]
Loans past due	4,930	10,797
Commercial Real Estate Portfolio Segment [Member] | Financial Asset, 60 to 89 Days Past Due [Member]
Loans past due	4,264	8,545
Commercial Real Estate Portfolio Segment [Member] | Financial Asset, Equal to or Greater than 90 Days Past Due [Member]
Loans past due	14,469	3,259
Residential Mortgage and Equity Lines Portfolio Segment [Member]
Loans past due	7,972	17,550
Non-accrual loans	7,461	7,527
Loans not past due	4,261,514	3,926,270
Loans	4,269,486	3,943,820
Residential Mortgage and Equity Lines Portfolio Segment [Member] | Financial Asset, 30 to 59 Days Past Due [Member]
Loans past due	0	9,687
Residential Mortgage and Equity Lines Portfolio Segment [Member] | Financial Asset, 60 to 89 Days Past Due [Member]
Loans past due	511	336
Residential Mortgage and Equity Lines Portfolio Segment [Member] | Financial Asset, Equal to or Greater than 90 Days Past Due [Member]
Loans past due	0	0
Installment and Other Loans [Member ]
Loans past due	0	0
Non-accrual loans	0	0
Loans not past due	6,631	4,349
Loans	6,631	4,349
Installment and Other Loans [Member ] | Financial Asset, 30 to 59 Days Past Due [Member]
Loans past due	0	0
Installment and Other Loans [Member ] | Financial Asset, 60 to 89 Days Past Due [Member]
Loans past due	0	0
Installment and Other Loans [Member ] | Financial Asset, Equal to or Greater than 90 Days Past Due [Member]
Loans past due	$ 0	$ 0