Loans and Allowance for Loan Losses (Narrative) (Details) $ in Thousands	3 Months Ended
	Mar. 31, 2018 USD ($) loan agreement	Mar. 31, 2017 USD ($) loan	Dec. 31, 2017 USD ($)
Accounts, Notes, Loans and Financing Receivable [Line Items]
Nonaccrual loans	$ 275,179		$ 252,800
TDRs both accruing and nonaccruing	284,500		219,700
Post-Modification outstanding recorded investment	$ 63,220	$ 45,092
Number of TDRs subsequently defaulted | loan	0	0
Unfunded commitment to borrowers related to modified TDR	$ 8,500		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	$ 118,000		99,200
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	48,400	$ 27,400
Troubled Debt Restructurings [Member] | Loans With Significant Covenant Waivers [Member]
Accounts, Notes, Loans and Financing Receivable [Line Items]
Convenant waivers	14,600	10,700
Troubled Debt Restructurings [Member] | Loans With Other Modifications [Member]
Accounts, Notes, Loans and Financing Receivable [Line Items]
Post-Modification outstanding recorded investment	$ 200
Other modifications		$ 6,900
FDIC Loss Share Agreement [Member]
Accounts, Notes, Loans and Financing Receivable [Line Items]
Number of loss share agreements | agreement	2
Consumer [Member]
Accounts, Notes, Loans and Financing Receivable [Line Items]
Nonaccrual loans	$ 14,163		15,087
Post-Modification outstanding recorded investment	222
Real estate in process of foreclosure	7,800		7,500
Real estate acquired through foreclosure	$ 3,700		$ 3,400