Loans And Allowance For Loan Losses (Narrative) (Details)	3 Months Ended								12 Months Ended
	Dec. 31, 2017 USD ($)	Sep. 30, 2017 USD ($)	Jun. 30, 2017 USD ($)	Mar. 31, 2017 USD ($)	Dec. 31, 2016 USD ($)	Sep. 30, 2016 USD ($)	Jun. 30, 2016 USD ($)	Mar. 31, 2016 USD ($)	Dec. 31, 2017 USD ($) Contract	Dec. 31, 2016 USD ($) Contract	Dec. 31, 2015 USD ($) Contract
Accounts, Notes, Loans and Financing Receivable [Line Items]
Loans and leases receivable, impaired, interest lost on nonaccrual loans									$ 9,100,000	$ 8,900,000
Interest income recognized									6,961,000	8,196,000
Average recorded investment in impaired loans									223,009,000	274,515,000	$ 358,300,000
Accrued interest income recognized											9,500,000
Investments income recognized in impairment loans, excluding TDRs									0	0	0
Impaired financing receivable, recorded investment, nonaccrual status	$ 49,000,000				$ 53,700,000				$ 49,000,000	$ 53,700,000	$ 77,900,000
Subsequent default, number of contracts | Contract									8	2	7
Accruing troubled debt restructuring	151,300,000				195,800,000				$ 151,300,000	$ 195,800,000
Provision for losses on loans	$ 8,565,000	$ 39,686,000	$ 10,260,000	$ 8,674,000	$ 6,259,000	$ 5,671,000	$ 6,693,000	$ 9,377,000	67,185,000	28,000,000	$ 19,010,000
Troubled Debt Restructurings That Subsequently Defaulted
Accounts, Notes, Loans and Financing Receivable [Line Items]
Modifications, post-modification recorded investment									4,000,000	181,000	$ 12,500,000
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									$ 2,700,000	3,500,000
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
Accruing TDRs With Modifications And Renewals Completed
Accounts, Notes, Loans and Financing Receivable [Line Items]
Provision for losses on loans									$ 8,700,000	$ 9,800,000