Loans and Allowance for Loan Losses (Narrative) (Details) $ in Thousands	3 Months Ended		6 Months Ended
	Jun. 30, 2018 USD ($) loan	Jun. 30, 2017 USD ($) loan	Jun. 30, 2018 USD ($) loan	Jun. 30, 2017 USD ($) loan	Dec. 31, 2017 USD ($)
Accounts, Notes, Loans and Financing Receivable [Line Items]
Nonaccrual loans	$ 241,681		$ 241,681		$ 252,800
TDRs both accruing and nonaccruing	251,300		251,300		219,700
Post-Modification outstanding recorded investment	6,552	$ 59,244	69,772	$ 104,336
Number of TDRs subsequently defaulted | loan		0		0
Unfunded commitment to borrowers related to modified TDR	9,700		9,700		7,300
TDRs and loans impaired with minimum aggregate relationship balances			$ 1,000
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	$ 98,800		$ 98,800		99,200
Number of TDRs subsequently defaulted | loan	1		1
Recorded investment	$ 200		$ 200
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			49,600	$ 28,400
Troubled Debt Restructurings [Member] | Loans With Significant Covenant Waivers [Member]
Accounts, Notes, Loans and Financing Receivable [Line Items]
Convenant waivers			14,600	40,200
Troubled Debt Restructurings [Member] | Loans With Other Modifications [Member]
Accounts, Notes, Loans and Financing Receivable [Line Items]
Post-Modification outstanding recorded investment			5,600
Other modifications				35,700
Consumer [Member]
Accounts, Notes, Loans and Financing Receivable [Line Items]
Nonaccrual loans	14,347		14,347		15,087
Post-Modification outstanding recorded investment		$ 42	222	$ 42
Real estate in process of foreclosure	6,200		6,200		7,500
Real estate acquired through foreclosure	$ 2,500		$ 2,500		$ 3,400