Loans and Allowance for Credit Losses (Narrative) (Details) $ in Thousands	3 Months Ended
	Mar. 31, 2020 USD ($) loan Customer	Mar. 31, 2019 USD ($) loan	Dec. 31, 2019 USD ($)
Accounts Notes And Loans Receivable [Line Items]
Accrued interest	$ 72,200		$ 67,700
Weighted average percentage of forecast	80.00%
Nonaccrual loans	$ 254,058		245,833
Estimated interest income from nonaccrual loans not assigned to nonaccrual status	4,300	$ 2,900
TDRs both accruing and nonaccruing	153,100		193,700
Unfunded commitment to borrowers related to modified TDR	8,100		2,400
TDRs and loans impaired with minimum aggregate relationship balances	$ 1,000
Number of customer loans excluded from TDR | Customer	1,618
Loans excluded from TDR disclosure	$ 839,400
Total Past Due	307,348		260,818
Recorded Investment > 90 Days and Accruing	17,790		6,582
Purchased with credit deterioration, increase	19,800
Consumer [Member]
Accounts Notes And Loans Receivable [Line Items]
Nonaccrual loans	17,903		16,374
Total Past Due	41,323		34,702
Recorded Investment > 90 Days and Accruing	1,259		1,638
Real estate in process of foreclosure			8,600
Real estate acquired through foreclosure	5,600		6,300
30-59 Days Past Due [Member]
Accounts Notes And Loans Receivable [Line Items]
Total Past Due	114,485		83,693
30-59 Days Past Due [Member] | Consumer [Member]
Accounts Notes And Loans Receivable [Line Items]
Total Past Due	24,002		18,586
60-89 Days Past Due [Member]
Accounts Notes And Loans Receivable [Line Items]
Total Past Due	18,031		30,183
60-89 Days Past Due [Member] | Consumer [Member]
Accounts Notes And Loans Receivable [Line Items]
Total Past Due	7,870		6,215
Greater Than 90 Days Past Due [Member]
Accounts Notes And Loans Receivable [Line Items]
Total Past Due	174,832		146,942
Greater Than 90 Days Past Due [Member] | Consumer [Member]
Accounts Notes And Loans Receivable [Line Items]
Total Past Due	9,451		9,901
Troubled Debt Restructurings [Member]
Accounts Notes And Loans Receivable [Line Items]
Nonaccrual loans	$ 117,900		132,500
Number of TDRs subsequently defaulted | loan	0	0
Troubled Debt Restructurings [Member] | Loans With Extended Amortization Terms Or Other Payment Concessions [Member]
Accounts Notes And Loans Receivable [Line Items]
Extended terms and other payment concessions	$ 300	$ 100
Troubled Debt Restructurings [Member] | Loans With Significant Covenant Waivers [Member]
Accounts Notes And Loans Receivable [Line Items]
Covenant waivers	400	8,800
Troubled Debt Restructurings [Member] | Loans With Other Modifications [Member]
Accounts Notes And Loans Receivable [Line Items]
Other modifications		$ 6,400
Prior to Adoption of CEFL [member]
Accounts Notes And Loans Receivable [Line Items]
Nonaccrual loans	$ 17,500
Recorded Investment > 90 Days and Accruing			8,300
Prior to Adoption of CEFL [member] | 30-59 Days Past Due [Member]
Accounts Notes And Loans Receivable [Line Items]
Total Past Due			6,100
Prior to Adoption of CEFL [member] | 60-89 Days Past Due [Member]
Accounts Notes And Loans Receivable [Line Items]
Total Past Due			2,000
Prior to Adoption of CEFL [member] | Greater Than 90 Days Past Due [Member]
Accounts Notes And Loans Receivable [Line Items]
Total Past Due			$ 8,300
Downside Scenario S-3 [Member]
Accounts Notes And Loans Receivable [Line Items]
Weighted average percentage of forecast	15.00%
Downside Scenario S-4 [Member]
Accounts Notes And Loans Receivable [Line Items]
Weighted average percentage of forecast	5.00%