Note 8 - Loans - Aging of Loan Portfolio (Details) - USD ($) $ in Thousands	Sep. 30, 2017	Dec. 31, 2016
Loans past due	$ 92,569	$ 126,826
Non-accrual loans	65,313	49,682
Loans not past due	12,504,865	11,074,449
Loans	12,597,434	11,201,275
Financing Receivables, 30 to 59 Days Past Due [Member]
Loans past due	8,412	43,419
Financing Receivables, 60 to 89 Days Past Due [Member]
Loans past due	14,944	33,725
Financing Receivables, Equal to Greater than 90 Days Past Due [Member]
Loans past due	3,900
Commercial Portfolio Segment [Member]
Loans past due	43,109	65,653
Non-accrual loans	15,942	15,710
Loans not past due	2,376,782	2,182,534
Loans	2,419,891	2,248,187
Commercial Portfolio Segment [Member] | Financing Receivables, 30 to 59 Days Past Due [Member]
Loans past due	8,412	22,753
Commercial Portfolio Segment [Member] | Financing Receivables, 60 to 89 Days Past Due [Member]
Loans past due	14,855	27,190
Commercial Portfolio Segment [Member] | Financing Receivables, Equal to Greater than 90 Days Past Due [Member]
Loans past due	3,900
Real Estate Construction Portfolio Segment [Member]
Loans past due	14,267	21,683
Non-accrual loans	14,267	5,458
Loans not past due	677,219	526,405
Loans	691,486	548,088
Real Estate Construction Portfolio Segment [Member] | Financing Receivables, 30 to 59 Days Past Due [Member]
Loans past due		10,390
Real Estate Construction Portfolio Segment [Member] | Financing Receivables, 60 to 89 Days Past Due [Member]
Loans past due		5,835
Real Estate Construction Portfolio Segment [Member] | Financing Receivables, Equal to Greater than 90 Days Past Due [Member]
Loans past due
Commercial Real Estate Portfolio Segment [Member]
Loans past due	28,379	26,664
Non-accrual loans	28,379	20,078
Loans not past due	6,348,668	5,758,584
Loans	6,377,047	5,785,248
Commercial Real Estate Portfolio Segment [Member] | Financing Receivables, 30 to 59 Days Past Due [Member]
Loans past due		5,886
Commercial Real Estate Portfolio Segment [Member] | Financing Receivables, 60 to 89 Days Past Due [Member]
Loans past due		700
Commercial Real Estate Portfolio Segment [Member] | Financing Receivables, Equal to Greater than 90 Days Past Due [Member]
Loans past due
Residential Mortgage and Equity Lines Portfolio Segment [Member]
Loans past due	6,814	12,826
Non-accrual loans	6,725	8,436
Loans not past due	3,097,474	2,602,933
Loans	3,104,288	2,615,759
Residential Mortgage and Equity Lines Portfolio Segment [Member] | Financing Receivables, 30 to 59 Days Past Due [Member]
Loans past due		4,390
Residential Mortgage and Equity Lines Portfolio Segment [Member] | Financing Receivables, 60 to 89 Days Past Due [Member]
Loans past due	89
Residential Mortgage and Equity Lines Portfolio Segment [Member] | Financing Receivables, Equal to 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	4,722	3,993
Loans	4,722	3,993
Installment and Other Loans [Member ] | Financing Receivables, 30 to 59 Days Past Due [Member]
Loans past due
Installment and Other Loans [Member ] | Financing Receivables, 60 to 89 Days Past Due [Member]
Loans past due
Installment and Other Loans [Member ] | Financing Receivables, Equal to Greater than 90 Days Past Due [Member]
Loans past due