Note 7 - Loans (Details) - Portfolio by Risk Rating (USD $) In Thousands, unless otherwise specified	Sep. 30, 2014	Dec. 31, 2013
Financing Receivable, Recorded Investment [Line Items]
Loans	$ 8,858,254	$ 8,084,563
Commercial Loans [Member] | Pass [Member]
Financing Receivable, Recorded Investment [Line Items]
Loans	2,283,837	2,108,191
Commercial Loans [Member] | Special Mention [Member]
Financing Receivable, Recorded Investment [Line Items]
Loans	82,731	84,786
Commercial Loans [Member] | Substandard [Member]
Financing Receivable, Recorded Investment [Line Items]
Loans	80,180	102,088
Commercial Loans [Member] | Doubtful [Member]
Financing Receivable, Recorded Investment [Line Items]
Loans	3,370	3,659
Commercial Loans [Member]
Financing Receivable, Recorded Investment [Line Items]
Loans	2,450,118	2,298,724
Real Estate Construction Loans [Member] | Pass [Member]
Financing Receivable, Recorded Investment [Line Items]
Loans	267,760	184,449
Real Estate Construction Loans [Member] | Substandard [Member]
Financing Receivable, Recorded Investment [Line Items]
Loans	32,199	33,939
Real Estate Construction Loans [Member] | Doubtful [Member]
Financing Receivable, Recorded Investment [Line Items]
Loans	1,500	3,313
Real Estate Construction Loans [Member]
Financing Receivable, Recorded Investment [Line Items]
Loans	301,459	221,701
Commercial Mortgage Loans [Member] | Pass [Member]
Financing Receivable, Recorded Investment [Line Items]
Loans	4,124,943	3,686,788
Commercial Mortgage Loans [Member] | Special Mention [Member]
Financing Receivable, Recorded Investment [Line Items]
Loans	112,825	127,436
Commercial Mortgage Loans [Member] | Substandard [Member]
Financing Receivable, Recorded Investment [Line Items]
Loans	176,299	208,827
Commercial Mortgage Loans [Member]
Financing Receivable, Recorded Investment [Line Items]
Loans	4,414,067	4,023,051
Residential Mortgage And Equity Lines Member | Pass [Member]
Financing Receivable, Recorded Investment [Line Items]
Loans	1,679,920	1,510,647
Residential Mortgage And Equity Lines Member | Substandard [Member]
Financing Receivable, Recorded Investment [Line Items]
Loans	9,014	15,885
Residential Mortgage And Equity Lines Member
Financing Receivable, Recorded Investment [Line Items]
Loans	1,688,934	1,526,532
Installment And Other Loans [Member] | Pass [Member]
Financing Receivable, Recorded Investment [Line Items]
Loans	3,676	14,555
Installment And Other Loans [Member]
Financing Receivable, Recorded Investment [Line Items]
Loans	3,676	14,555
Pass [Member]
Financing Receivable, Recorded Investment [Line Items]
Loans	8,360,136	7,504,630
Special Mention [Member]
Financing Receivable, Recorded Investment [Line Items]
Loans	195,556	212,222
Substandard [Member]
Financing Receivable, Recorded Investment [Line Items]
Loans	297,692	360,739
Doubtful [Member]
Financing Receivable, Recorded Investment [Line Items]
Loans	$ 4,870	$ 6,972