Loans and Allowance for Loan Losses (Narrative) (Details)	3 Months Ended		9 Months Ended
	Sep. 30, 2018 USD ($)	Sep. 30, 2017 USD ($)	Sep. 30, 2018 USD ($) loan	Sep. 30, 2017 USD ($) loan	Dec. 31, 2017 USD ($)
Accounts, Notes, Loans and Financing Receivable [Line Items]
Nonaccrual loans	$ 201,646,000		$ 201,646,000		$ 252,800,000
TDRs both accruing and nonaccruing	254,900,000		254,900,000		219,700,000
Post-Modification outstanding recorded investment	24,595,000	$ 43,118,000	94,367,000	$ 147,454,000
Unfunded commitment to borrowers related to modified TDR	8,200,000		8,200,000		7,300,000
TDRs and loans impaired with minimum aggregate relationship balances			$ 1,000,000
Performing [Member]
Accounts, Notes, Loans and Financing Receivable [Line Items]
Period for which payments of principal and interest are past due			less than 90 days
Troubled Debt Restructurings [Member]
Accounts, Notes, Loans and Financing Receivable [Line Items]
Nonaccrual loans	92,700,000		$ 92,700,000		99,200,000
Number of TDRs subsequently defaulted | loan			1	0
Recorded investment			$ 200,000
Troubled Debt Restructurings [Member] | Loans With Extended Amortization Terms Or Other Payment Concessions [Member]
Accounts, Notes, Loans and Financing Receivable [Line Items]
Extended terms and other payment concessions			50,700,000	$ 96,100,000
Troubled Debt Restructurings [Member] | Loans With Significant Covenant Waivers [Member]
Accounts, Notes, Loans and Financing Receivable [Line Items]
Convenant waivers			14,600,000	50,100,000
Troubled Debt Restructurings [Member] | Loans With Other Modifications [Member]
Accounts, Notes, Loans and Financing Receivable [Line Items]
Post-Modification outstanding recorded investment			29,100,000
Other modifications				1,300,000
Consumer [Member]
Accounts, Notes, Loans and Financing Receivable [Line Items]
Nonaccrual loans	15,576,000		15,576,000		15,087,000
Post-Modification outstanding recorded investment	89,000		311,000	$ 42,000
Real estate in process of foreclosure	6,900,000		6,900,000		7,500,000
Real estate acquired through foreclosure	$ 1,900,000		$ 1,900,000		$ 3,400,000