Loans and Allowance for Loan Losses (Narrative) (Details) - USD ($)	3 Months Ended		12 Months Ended
	Mar. 31, 2018	Mar. 31, 2017	Dec. 31, 2017
Accounts, Notes, Loans and Financing Receivable [Line Items]
Average recorded investment in impaired loans	$ 198,131,000	$ 235,600,000	$ 223,009,000
Interest income recognized	1,430,000	0	6,961,000
Interest income recognized for accruing TDRs		1,700,000
Non-accrual status	62,200,000		49,000,000
Provision for loan losses	12,776,000	$ 8,674,000
Accruing TDRs With Modifications And Renewals Completed
Accounts, Notes, Loans and Financing Receivable [Line Items]
Accruing troubled debt restructuring	129,400,000
Provision for loan losses	$ 6,100,000		8,700,000
Substandard
Accounts, Notes, Loans and Financing Receivable [Line Items]
Retail loan substandard period (in days)	90 days
Loss And Charged Off
Accounts, Notes, Loans and Financing Receivable [Line Items]
Retail loans downgraded to loss (in days)	120 days
Accruing TDRs With Modifications And Renewals Completed
Accounts, Notes, Loans and Financing Receivable [Line Items]
Accruing troubled debt restructuring			$ 151,300,000
Accruing TDRs With Modifications And Renewals Completed | Minimum
Accounts, Notes, Loans and Financing Receivable [Line Items]
Commercial-type impaired loans	$ 1,000,000