Note 7 - Loans (Details) - Portfolio by Risk Rating - USD ($)	Jun. 30, 2015	Dec. 31, 2014
Financing Receivable, Recorded Investment [Line Items]
Loans	$ 9,502,008,000	$ 8,914,080,000
Loans held for sale	0	973,000
Pass [Member]
Financing Receivable, Recorded Investment [Line Items]
Loans	9,063,634,000	8,483,654,000
Special Mention [Member]
Financing Receivable, Recorded Investment [Line Items]
Loans	179,318,000	153,589,000
Substandard [Member]
Financing Receivable, Recorded Investment [Line Items]
Loans	247,494,000	274,498,000
Loans held for sale		973,000
Doubtful [Member]
Financing Receivable, Recorded Investment [Line Items]
Loans	11,562,000	2,339,000
Commercial Portfolio Segment [Member]
Financing Receivable, Recorded Investment [Line Items]
Loans	2,387,450,000	2,382,493,000
Commercial Portfolio Segment [Member] | Pass [Member]
Financing Receivable, Recorded Investment [Line Items]
Loans	2,251,083,000	2,260,474,000
Commercial Portfolio Segment [Member] | Special Mention [Member]
Financing Receivable, Recorded Investment [Line Items]
Loans	64,655,000	47,619,000
Commercial Portfolio Segment [Member] | Substandard [Member]
Financing Receivable, Recorded Investment [Line Items]
Loans	70,240,000	72,561,000
Commercial Portfolio Segment [Member] | Doubtful [Member]
Financing Receivable, Recorded Investment [Line Items]
Loans	1,472,000	1,839,000
Real Estate Construction Portfolio Segment [Member]
Financing Receivable, Recorded Investment [Line Items]
Loans	370,828,000	298,654,000
Real Estate Construction Portfolio Segment [Member] | Pass [Member]
Financing Receivable, Recorded Investment [Line Items]
Loans	348,242,000	272,927,000
Real Estate Construction Portfolio Segment [Member] | Substandard [Member]
Financing Receivable, Recorded Investment [Line Items]
Loans	22,086,000	25,227,000
Real Estate Construction Portfolio Segment [Member] | Doubtful [Member]
Financing Receivable, Recorded Investment [Line Items]
Loans	500,000	500,000
Commercial Real Estate Portfolio Segment [Member]
Financing Receivable, Recorded Investment [Line Items]
Loans	4,849,381,000	4,486,443,000
Commercial Real Estate Portfolio Segment [Member] | Pass [Member]
Financing Receivable, Recorded Investment [Line Items]
Loans	4,580,231,000	4,213,453,000
Commercial Real Estate Portfolio Segment [Member] | Special Mention [Member]
Financing Receivable, Recorded Investment [Line Items]
Loans	114,663,000	105,970,000
Commercial Real Estate Portfolio Segment [Member] | Substandard [Member]
Financing Receivable, Recorded Investment [Line Items]
Loans	144,897,000	167,020,000
Commercial Real Estate Portfolio Segment [Member] | Doubtful [Member]
Financing Receivable, Recorded Investment [Line Items]
Loans	9,590,000
Residential Mortgage and Equity Lines Portfolio Segment [Member]
Financing Receivable, Recorded Investment [Line Items]
Loans	1,889,379,000	1,742,938,000
Residential Mortgage and Equity Lines Portfolio Segment [Member] | Pass [Member]
Financing Receivable, Recorded Investment [Line Items]
Loans	1,879,108,000	1,733,248,000
Residential Mortgage and Equity Lines Portfolio Segment [Member] | Substandard [Member]
Financing Receivable, Recorded Investment [Line Items]
Loans	10,271,000	9,690,000
Consumer Portfolio Segment [Member]
Financing Receivable, Recorded Investment [Line Items]
Loans	4,970,000	3,552,000
Consumer Portfolio Segment [Member] | Pass [Member]
Financing Receivable, Recorded Investment [Line Items]
Loans	$ 4,970,000	$ 3,552,000