Loans and Leases (Loans Acquired By Loan Class) (Details) - USD ($) $ in Thousands	Dec. 31, 2019	Dec. 31, 2018	Dec. 31, 2017	Dec. 31, 2016
Accounts, Notes, Loans and Financing Receivable [Line Items]
Loans and leases, not acquired in a transfer accounted for as debt securities	$ 28,322,780	$ 24,916,700
PCI Loans	558,716	606,576	$ 762,998	$ 809,169
Commercial
Accounts, Notes, Loans and Financing Receivable [Line Items]
Loans and leases, not acquired in a transfer accounted for as debt securities	18,552,002	16,137,227
PCI Loans	284,329	296,672
Commercial | Construction and land development
Accounts, Notes, Loans and Financing Receivable [Line Items]
Loans and leases, not acquired in a transfer accounted for as debt securities	1,013,454	757,854
Commercial | Mortgage
Accounts, Notes, Loans and Financing Receivable [Line Items]
Loans and leases, not acquired in a transfer accounted for as debt securities	12,282,635	10,717,234
Commercial | Other commercial real estate
Accounts, Notes, Loans and Financing Receivable [Line Items]
Loans and leases, not acquired in a transfer accounted for as debt securities	542,028	426,985
Commercial | Commercial and industrial
Accounts, Notes, Loans and Financing Receivable [Line Items]
Loans and leases, not acquired in a transfer accounted for as debt securities	4,403,792	3,938,730
Commercial | Other
Accounts, Notes, Loans and Financing Receivable [Line Items]
Loans and leases, not acquired in a transfer accounted for as debt securities	310,093	296,424
Noncommercial
Accounts, Notes, Loans and Financing Receivable [Line Items]
Loans and leases, not acquired in a transfer accounted for as debt securities	9,770,778	8,779,473
Noncommercial | Construction and land development
Accounts, Notes, Loans and Financing Receivable [Line Items]
Loans and leases, not acquired in a transfer accounted for as debt securities	357,385	257,030
Noncommercial | Mortgage
Accounts, Notes, Loans and Financing Receivable [Line Items]
Loans and leases, not acquired in a transfer accounted for as debt securities	5,293,917	4,265,687
Noncommercial | Revolving mortgage
Accounts, Notes, Loans and Financing Receivable [Line Items]
Loans and leases, not acquired in a transfer accounted for as debt securities	2,339,072	2,542,975
Noncommercial | Consumer
Accounts, Notes, Loans and Financing Receivable [Line Items]
Loans and leases, not acquired in a transfer accounted for as debt securities	1,780,404	1,713,781
Pass | Commercial
Accounts, Notes, Loans and Financing Receivable [Line Items]
Loans and leases, not acquired in a transfer accounted for as debt securities	18,157,655	15,757,669
PCI Loans	148,412	141,922
Pass | Commercial | Construction and land development
Accounts, Notes, Loans and Financing Receivable [Line Items]
Loans and leases, not acquired in a transfer accounted for as debt securities	1,004,922	753,985
Pass | Commercial | Mortgage
Accounts, Notes, Loans and Financing Receivable [Line Items]
Loans and leases, not acquired in a transfer accounted for as debt securities	12,050,799	10,507,687
Pass | Commercial | Other commercial real estate
Accounts, Notes, Loans and Financing Receivable [Line Items]
Loans and leases, not acquired in a transfer accounted for as debt securities	536,682	422,500
Pass | Commercial | Commercial and industrial
Accounts, Notes, Loans and Financing Receivable [Line Items]
Loans and leases, not acquired in a transfer accounted for as debt securities	4,256,456	3,778,797
Pass | Commercial | Other
Accounts, Notes, Loans and Financing Receivable [Line Items]
Loans and leases, not acquired in a transfer accounted for as debt securities	308,796	294,700
Special mention | Commercial
Accounts, Notes, Loans and Financing Receivable [Line Items]
Loans and leases, not acquired in a transfer accounted for as debt securities	166,866	174,700
PCI Loans	44,290	48,475
Special mention | Commercial | Construction and land development
Accounts, Notes, Loans and Financing Receivable [Line Items]
Loans and leases, not acquired in a transfer accounted for as debt securities	2,577	1,369
Special mention | Commercial | Mortgage
Accounts, Notes, Loans and Financing Receivable [Line Items]
Loans and leases, not acquired in a transfer accounted for as debt securities	115,164	114,219
Special mention | Commercial | Other commercial real estate
Accounts, Notes, Loans and Financing Receivable [Line Items]
Loans and leases, not acquired in a transfer accounted for as debt securities	3,899	3,193
Special mention | Commercial | Commercial and industrial
Accounts, Notes, Loans and Financing Receivable [Line Items]
Loans and leases, not acquired in a transfer accounted for as debt securities	44,604	54,814
Special mention | Commercial | Other
Accounts, Notes, Loans and Financing Receivable [Line Items]
Loans and leases, not acquired in a transfer accounted for as debt securities	622	1,105
Substandard | Commercial
Accounts, Notes, Loans and Financing Receivable [Line Items]
Loans and leases, not acquired in a transfer accounted for as debt securities	158,897	127,842
PCI Loans	87,970	101,447
Substandard | Commercial | Construction and land development
Accounts, Notes, Loans and Financing Receivable [Line Items]
Loans and leases, not acquired in a transfer accounted for as debt securities	5,955	2,500
Substandard | Commercial | Mortgage
Accounts, Notes, Loans and Financing Receivable [Line Items]
Loans and leases, not acquired in a transfer accounted for as debt securities	116,672	92,743
Substandard | Commercial | Other commercial real estate
Accounts, Notes, Loans and Financing Receivable [Line Items]
Loans and leases, not acquired in a transfer accounted for as debt securities	1,447	1,292
Substandard | Commercial | Commercial and industrial
Accounts, Notes, Loans and Financing Receivable [Line Items]
Loans and leases, not acquired in a transfer accounted for as debt securities	34,148	30,688
Substandard | Commercial | Other
Accounts, Notes, Loans and Financing Receivable [Line Items]
Loans and leases, not acquired in a transfer accounted for as debt securities	675	619
Doubtful | Commercial
Accounts, Notes, Loans and Financing Receivable [Line Items]
Loans and leases, not acquired in a transfer accounted for as debt securities	3	354
PCI Loans	3,657	4,828
Doubtful | Commercial | Construction and land development
Accounts, Notes, Loans and Financing Receivable [Line Items]
Loans and leases, not acquired in a transfer accounted for as debt securities	0	0
Doubtful | Commercial | Mortgage
Accounts, Notes, Loans and Financing Receivable [Line Items]
Loans and leases, not acquired in a transfer accounted for as debt securities	0	0
Doubtful | Commercial | Other commercial real estate
Accounts, Notes, Loans and Financing Receivable [Line Items]
Loans and leases, not acquired in a transfer accounted for as debt securities	0	0
Doubtful | Commercial | Commercial and industrial
Accounts, Notes, Loans and Financing Receivable [Line Items]
Loans and leases, not acquired in a transfer accounted for as debt securities	3	354
Doubtful | Commercial | Other
Accounts, Notes, Loans and Financing Receivable [Line Items]
Loans and leases, not acquired in a transfer accounted for as debt securities	0	0
Ungraded | Commercial
Accounts, Notes, Loans and Financing Receivable [Line Items]
Loans and leases, not acquired in a transfer accounted for as debt securities	68,581	76,662
PCI Loans	0	0
Ungraded | Commercial | Construction and land development
Accounts, Notes, Loans and Financing Receivable [Line Items]
Loans and leases, not acquired in a transfer accounted for as debt securities	0	0
Ungraded | Commercial | Mortgage
Accounts, Notes, Loans and Financing Receivable [Line Items]
Loans and leases, not acquired in a transfer accounted for as debt securities	0	2,585
Ungraded | Commercial | Other commercial real estate
Accounts, Notes, Loans and Financing Receivable [Line Items]
Loans and leases, not acquired in a transfer accounted for as debt securities	0	0
Ungraded | Commercial | Commercial and industrial
Accounts, Notes, Loans and Financing Receivable [Line Items]
Loans and leases, not acquired in a transfer accounted for as debt securities	68,581	74,077
Ungraded | Commercial | Other
Accounts, Notes, Loans and Financing Receivable [Line Items]
Loans and leases, not acquired in a transfer accounted for as debt securities	$ 0	$ 0