Loans, Allowance for Credit Losses, and Credit Quality (Details Textuals) - USD ($) $ in Thousands	3 Months Ended		9 Months Ended
	Sep. 30, 2015	Sep. 30, 2014	Sep. 30, 2015	Sep. 30, 2014	Dec. 31, 2014	Dec. 31, 2013
Receivables [Abstract]
Reclassified Loans	$ 500,000		$ 500,000
Balance Prior to Reclassification, Consumer, Home Equity					$ 1,600,000
Balance Prior to Reclassification, Consumer, Mortgage					4,500,000
Home equity	1,014,465		1,014,465		1,051,927
Residential mortgage	5,682,178		5,682,178		5,056,891
Financing Receivable, Allowance for Credit Losses [Line Items]
Loans and Leases Receivable, Allowance	262,536		262,536		266,302	$ 268,315
Recorded Investment	5,056	$ 18,504	17,713	$ 26,373
Restructured Loans Subsequently Accruing	2,000		2,000
YTD Restructured Loans Still On Nonaccrual	16,000		16,000
Commercial and Industrial [Member]
Financing Receivable, Allowance for Credit Losses [Line Items]
Loans and Leases Receivable, Allowance	118,494		118,494		116,025	$ 104,501
Commercial and Industrial [Member] | Oil and Gas Industry [Member]
Financing Receivable, Allowance for Credit Losses [Line Items]
Loans and Leases Receivable, Allowance	$ 29,000		$ 29,000		$ 17,000
Allocated allowance for loan losses, percent	3.83%		3.83%		2.26%