Note 8 - Loans - Aging of Loan Portfolio (Details) - USD ($) $ in Thousands	Mar. 31, 2019	Dec. 31, 2018
Loans past due	$ 128,946	$ 106,057
Non-accrual loans	56,683	41,815
Loans not past due	14,148,476	13,889,731
Loans	14,277,422	13,995,788
Financial Asset, 30 to 59 Days Past Due [Member]
Loans past due	66,846	45,978
Financial Asset, 60 to 89 Days Past Due [Member]
Loans past due	5,417	14,491
Financial Asset, Equal to or Greater than 90 Days Past Due [Member]
Loans past due		3,773
Commercial Portfolio Segment [Member]
Loans past due	39,210	47,267
Non-accrual loans	26,499	18,805
Loans not past due	2,696,985	2,694,698
Loans	2,736,195	2,741,965
Commercial Portfolio Segment [Member] | Financial Asset, 30 to 59 Days Past Due [Member]
Loans past due	10,618	25,494
Commercial Portfolio Segment [Member] | Financial Asset, 60 to 89 Days Past Due [Member]
Loans past due	2,093	2,454
Commercial Portfolio Segment [Member] | Financial Asset, Equal to or Greater than 90 Days Past Due [Member]
Loans past due		514
Real Estate Construction Portfolio Segment [Member]
Loans past due	24,624	8,028
Non-accrual loans	4,801	4,872
Loans not past due	543,165	573,426
Loans	567,789	581,454
Real Estate Construction Portfolio Segment [Member] | Financial Asset, 30 to 59 Days Past Due [Member]
Loans past due	19,823
Real Estate Construction Portfolio Segment [Member] | Financial Asset, 60 to 89 Days Past Due [Member]
Loans past due		3,156
Real Estate Construction Portfolio Segment [Member] | Financial Asset, Equal to or Greater than 90 Days Past Due [Member]
Loans past due
Commercial Real Estate Portfolio Segment [Member]
Loans past due	45,371	33,212
Non-accrual loans	17,940	10,611
Loans not past due	6,843,527	6,690,988
Loans	6,888,898	6,724,200
Commercial Real Estate Portfolio Segment [Member] | Financial Asset, 30 to 59 Days Past Due [Member]
Loans past due	24,107	10,797
Commercial Real Estate Portfolio Segment [Member] | Financial Asset, 60 to 89 Days Past Due [Member]
Loans past due	3,324	8,545
Commercial Real Estate Portfolio Segment [Member] | Financial Asset, Equal to or Greater than 90 Days Past Due [Member]
Loans past due		3,259
Residential Mortgage and Equity Lines Portfolio Segment [Member]
Loans past due	19,741	17,550
Non-accrual loans	7,443	7,527
Loans not past due	4,057,166	3,926,270
Loans	4,076,907	3,943,820
Residential Mortgage and Equity Lines Portfolio Segment [Member] | Financial Asset, 30 to 59 Days Past Due [Member]
Loans past due	12,298	9,687
Residential Mortgage and Equity Lines Portfolio Segment [Member] | Financial Asset, 60 to 89 Days Past Due [Member]
Loans past due		336
Residential Mortgage and Equity Lines Portfolio Segment [Member] | Financial Asset, Equal to or Greater than 90 Days Past Due [Member]
Loans past due
Installment and Other Loans [Member ]
Loans past due
Non-accrual loans
Loans not past due	7,633	4,349
Loans	7,633	4,349
Installment and Other Loans [Member ] | Financial Asset, 30 to 59 Days Past Due [Member]
Loans past due
Installment and Other Loans [Member ] | Financial Asset, 60 to 89 Days Past Due [Member]
Loans past due
Installment and Other Loans [Member ] | Financial Asset, Equal to or Greater than 90 Days Past Due [Member]
Loans past due