Note 8 - Loans (Details Textual) - USD ($) $ in Thousands	6 Months Ended
	Jun. 30, 2020	Dec. 31, 2019	Jun. 30, 2019
Impaired Financing Receivable, Recorded Investment, Total	$ 88,129	$ 75,859
Percentage Of Charge Off To Contractual Balances For Impaired Loans	0.30%	2.10%
Financing Receivables, Impaired, Troubled Debt Restructuring, Specific Reserve	$ 86		$ 37
Financing Receivable, Troubled Debt Restructuring, Subsequent Default	0
Financing Receivable, Troubled Debt Restructuring, Commitment to Lend		$ 0
Loans and Leases Receivable, Gross, Total	15,608,283	15,075,481
Commercial Real Estate Portfolio Segment [Member]
Loans and Leases Receivable, Gross, Total	$ 7,391,502	7,275,262
Financing Receivable, Number of Contracts with Modifications	723
Loans and Leases Receivable with Modifications, Gross	$ 1,500,000
Financing Receivable with Modifications, Percentage of Total Commercial Real Estate Loans	21.00%
Commercial Portfolio Segment [Member]
Financing Receivables, Impaired, Troubled Debt Restructuring, Specific Reserve	$ 86		$ 37
Loans and Leases Receivable, Gross, Total	$ 3,007,966	2,778,744
Financing Receivable, Number of Contracts with Modifications	81
Loans and Leases Receivable with Modifications, Gross	$ 141,600
Financing Receivable, Percentage of Total Modified Commercial Loans	4.70%
Residential Portfolio Segment [Member]
Loans and Leases Receivable, Gross, Total	$ 4,184,721	4,088,586
Financing Receivable, Number of Contracts with Approved Forbearance Requests	1,198
Loans and Leases Receivable with Approved Forbearance Requests, Gross	$ 518,100
Financing Receivable, Approved Forbearance Percentage of Total Residential Mortgage Loans	12.40%
SBA's Paycheck Protection Program [Member]
Financing Receivable, Number of Contracts	1,381
Loans and Leases Receivable, Gross, Total	$ 261,700
Minimum [Member]
Period Loan Is In Payment Default (Day)	60 days
Maximum [Member]
Period Loan Is In Payment Default (Day)	90 days
Nonaccrual Loans [Member]
Impaired Financing Receivable, Recorded Investment, Total	$ 56,400	40,500
Accruing Troubled Debt Restructuring [Member]
Impaired Financing Receivable, Recorded Investment, Total	31,700	35,400
Financing Receivable, Troubled Debt Restructuring	31,700	35,300
Troubled Debt Restructuring, Specific Reserves	432,000
Financing Receivables, Impaired, Troubled Debt Restructuring, Specific Reserve	822
Non-accruing Troubled Debt Restructuring [Member]
Financing Receivable, Troubled Debt Restructuring	12,700	18,000
Troubled Debt Restructuring, Specific Reserves	$ 53,000
Financing Receivables, Impaired, Troubled Debt Restructuring, Specific Reserve		$ 2,200