Loans and Allowance for Loan Losses (Narrative) (Details) $ in Thousands	12 Months Ended
	Dec. 31, 2017 USD ($) agreement loan	Dec. 31, 2016 USD ($) loan	Dec. 31, 2015 USD ($) loan
Accounts, Notes, Loans and Financing Receivable [Line Items]
Nonaccrual loans	$ 252,800	$ 317,970
TDRs both accruing and nonaccruing	219,700	121,700
Post-Modification outstanding recorded investment	$ 177,070	$ 132,234	$ 5,107
Number of TDRs subsequently defaulted | loan	0	4	0
Recorded investment		$ 20,800
Unfunded commitment to borrowers related to modified TDR	$ 7,300	6,800
TDRs and loans impaired with minimum aggregate relationship balances	1,000
Loans covered by loss share agreement		149,000
Related party balances of loans	33,600	15,300
Related party new loans	25,800
Related party repayments	7,500
Loss on termination of loss share agreements	(6,603)
Cash received from FDIC for final settlement of agreements	(3,234)
Loans held for sale	39,865	34,064
Short-term borrowings	1,703,890	1,225,406
FHLB Borrowings [Member]
Accounts, Notes, Loans and Financing Receivable [Line Items]
Short-term borrowings	1,132,567	865,000
Troubled Debt Restructurings [Member]
Accounts, Notes, Loans and Financing Receivable [Line Items]
Nonaccrual loans	99,200	81,900
Troubled Debt Restructurings [Member] | Loans With Extended Amortization Terms Or Other Payment Concessions [Member]
Accounts, Notes, Loans and Financing Receivable [Line Items]
Post-Modification outstanding recorded investment	98,100	108,900	$ 5,000
Troubled Debt Restructurings [Member] | Loans With Significant Covenant Waivers [Member]
Accounts, Notes, Loans and Financing Receivable [Line Items]
Convenant waivers	76,200	22,800
Troubled Debt Restructurings [Member] | Loans With Other Modifications [Member]
Accounts, Notes, Loans and Financing Receivable [Line Items]
Other modifications	$ 2,800	500	100
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	$ 15,087	12,351
Post-Modification outstanding recorded investment	40		$ 20
Real estate in process of foreclosure	7,500	10,100
Real estate acquired through foreclosure	$ 3,400	3,100
Consumer [Member] | FDIC Loss Share Agreement [Member]
Accounts, Notes, Loans and Financing Receivable [Line Items]
Real estate in process of foreclosure		4,900
Real estate acquired through foreclosure		$ 900