Loans and Allowance for Credit Losses (Loans, Net of Unearned Income) (Details) - USD ($) $ in Thousands	Mar. 31, 2022	Dec. 31, 2021	Mar. 31, 2021
Accounts Notes And Loans Receivable [Line Items]
Total loans	$ 21,323,341	$ 21,134,282	$ 21,664,859
Residential Mortgages [Member]
Accounts Notes And Loans Receivable [Line Items]
Total loans	2,462,900	2,423,890	2,488,792
Consumer [Member]
Accounts Notes And Loans Receivable [Line Items]
Total loans	1,557,774	1,583,390	1,756,452
Commercial Real Estate - Income Producing [Member] | Total Commercial [Member]
Accounts Notes And Loans Receivable [Line Items]
Total loans	3,563,299	3,464,626	3,411,028
Construction and Land Development [Member] | Total Commercial [Member]
Accounts Notes And Loans Receivable [Line Items]
Total loans	1,286,655	1,228,670	1,122,141
Total Commercial And Industrial [Member] | Total Commercial [Member]
Accounts Notes And Loans Receivable [Line Items]
Total loans	12,452,713	12,433,706	12,886,446
Total Commercial And Industrial [Member] | Commercial Non-Real Estate [Member] | Total Commercial [Member]
Accounts Notes And Loans Receivable [Line Items]
Total loans	9,584,480	9,612,460	10,091,342
Total Commercial And Industrial [Member] | Commercial Real Estate - Owner Occupied [Member] | Total Commercial [Member]
Accounts Notes And Loans Receivable [Line Items]
Total loans	$ 2,868,233	$ 2,821,246	$ 2,795,104