Loans And Allowance For Loan Losses (Narrative) (Details)	3 Months Ended								12 Months Ended
	Dec. 31, 2018 USD ($)	Sep. 30, 2018 USD ($)	Jun. 30, 2018 USD ($)	Mar. 31, 2018 USD ($)	Dec. 31, 2017 USD ($)	Sep. 30, 2017 USD ($)	Jun. 30, 2017 USD ($)	Mar. 31, 2017 USD ($)	Dec. 31, 2018 USD ($) contract	Dec. 31, 2017 USD ($) contract	Dec. 31, 2016 USD ($) contract
Accounts, Notes, Loans and Financing Receivable [Line Items]
Loans and leases receivable, impaired, interest lost on nonaccrual loans									$ 7,300,000	$ 9,100,000
Interest income recognized									7,216,000	7,777,000	$ 9,207,000
Loans pledged as collateral	$ 8,400,000,000				$ 7,930,000,000				8,400,000,000	7,930,000,000
Average recorded investment in impaired loans									181,869,000	212,969,000	264,608,000
Investments income recognized in impairment loans, excluding TDRs										0	0
Impaired financing receivable, recorded investment, nonaccrual status	51,300,000				49,000,000				51,300,000	49,000,000	53,700,000
Modifications, post-modification recorded investment									49,827,000	36,723,000	52,994,000
Provision for losses on loans	12,149,000	$ 14,982,000	$ 11,790,000	$ 12,776,000	8,565,000	$ 39,686,000	$ 10,260,000	$ 8,674,000	51,697,000	67,185,000	$ 28,000,000
Accruing TDRs With Modifications And Renewals Completed
Accounts, Notes, Loans and Financing Receivable [Line Items]
Accruing troubled debt restructuring	$ 115,600,000				$ 151,300,000				115,600,000	151,300,000
Provision for losses on loans									$ 6,100,000	$ 8,700,000
Troubled Debt Restructuring That Subsequently Defaulted
Accounts, Notes, Loans and Financing Receivable [Line Items]
Subsequent default, number of contracts | contract									8	8	2
Modifications, post-modification recorded investment									$ 10,500,000	$ 4,000,000	$ 181,000
Minimum
Accounts, Notes, Loans and Financing Receivable [Line Items]
Commercial-type impaired loans									1,000,000
Interest Income Recorded
Accounts, Notes, Loans and Financing Receivable [Line Items]
Interest income recognized									$ 3,200,000	$ 2,700,000
Loss And Charged Off
Accounts, Notes, Loans and Financing Receivable [Line Items]
Retail loan charge-off period (in days)									120 days
Substandard
Accounts, Notes, Loans and Financing Receivable [Line Items]
Retail loan substandard period (in days)									90 days