Loans and Allowance for Credit Losses (Loans, Net of Unearned Income) (Details) - USD ($) $ in Thousands	Jun. 30, 2020	Dec. 31, 2019	Jun. 30, 2019
Accounts Notes And Loans Receivable [Line Items]
Total loans	$ 22,628,377	$ 21,212,755	$ 20,175,812
Residential Mortgages [Member]
Accounts Notes And Loans Receivable [Line Items]
Total loans	2,877,316	2,990,631	2,968,271
Consumer [Member]
Accounts Notes And Loans Receivable [Line Items]
Total loans	2,044,264	2,164,818	2,088,923
Commercial Real Estate - Income Producing [Member] | Total Commercial [Member]
Accounts Notes And Loans Receivable [Line Items]
Total loans	3,350,299	2,994,448	2,895,468
Construction and Land Development [Member] | Total Commercial [Member]
Accounts Notes And Loans Receivable [Line Items]
Total loans	1,128,959	1,157,451	1,144,062
Total Commercial And Industrial [Member] | Total Commercial [Member]
Accounts Notes And Loans Receivable [Line Items]
Total loans	13,227,539	11,905,407	11,079,088
Total Commercial And Industrial [Member] | Commercial Non-Real Estate [Member] | Total Commercial [Member]
Accounts Notes And Loans Receivable [Line Items]
Total loans	10,465,280	9,166,947	8,559,118
Total Commercial And Industrial [Member] | Commercial Real Estate - Owner Occupied [Member] | Total Commercial [Member]
Accounts Notes And Loans Receivable [Line Items]
Total loans	$ 2,762,259	$ 2,738,460	$ 2,519,970