Loans and Allowance for Credit Losses (Age Analysis of Past Due Loans by Portfolio Class) (Details) - USD ($) $ in Thousands	Dec. 31, 2019	Dec. 31, 2018
Financing Receivable, Recorded Investment, Past Due [Line Items]
Total Past Due	$ 260,818	$ 237,050
Current	20,951,937	19,789,361
Total loans	21,212,755	20,026,411
Recorded Investment > 90 Days and Accruing	6,582	14,309
30-59 Days Past Due [Member]
Financing Receivable, Recorded Investment, Past Due [Line Items]
Total Past Due	83,693	77,690
60-89 Days Past Due [Member]
Financing Receivable, Recorded Investment, Past Due [Line Items]
Total Past Due	30,183	26,767
Greater Than 90 Days Past Due [Member]
Financing Receivable, Recorded Investment, Past Due [Line Items]
Total Past Due	146,942	132,593
Total Commercial [Member] | Commercial Real Estate - Income Producing [Member]
Financing Receivable, Recorded Investment, Past Due [Line Items]
Total Past Due	4,351	8,638
Current	2,990,097	2,333,141
Total loans	2,994,448	2,341,779
Recorded Investment > 90 Days and Accruing	450	1,844
Total Commercial [Member] | Construction and Land Development [Member]
Financing Receivable, Recorded Investment, Past Due [Line Items]
Total Past Due	8,907	10,691
Current	1,148,544	1,537,644
Total loans	1,157,451	1,548,335
Recorded Investment > 90 Days and Accruing	2,042	644
Total Commercial [Member] | 30-59 Days Past Due [Member] | Commercial Real Estate - Income Producing [Member]
Financing Receivable, Recorded Investment, Past Due [Line Items]
Total Past Due	738	2,371
Total Commercial [Member] | 30-59 Days Past Due [Member] | Construction and Land Development [Member]
Financing Receivable, Recorded Investment, Past Due [Line Items]
Total Past Due	5,747	7,397
Total Commercial [Member] | 60-89 Days Past Due [Member] | Commercial Real Estate - Income Producing [Member]
Financing Receivable, Recorded Investment, Past Due [Line Items]
Total Past Due	703	772
Total Commercial [Member] | 60-89 Days Past Due [Member] | Construction and Land Development [Member]
Financing Receivable, Recorded Investment, Past Due [Line Items]
Total Past Due	680	1,129
Total Commercial [Member] | Greater Than 90 Days Past Due [Member] | Commercial Real Estate - Income Producing [Member]
Financing Receivable, Recorded Investment, Past Due [Line Items]
Total Past Due	2,910	5,495
Total Commercial [Member] | Greater Than 90 Days Past Due [Member] | Construction and Land Development [Member]
Financing Receivable, Recorded Investment, Past Due [Line Items]
Total Past Due	2,480	2,165
Total Commercial [Member] | Total Commercial And Industrial [Member]
Financing Receivable, Recorded Investment, Past Due [Line Items]
Total Past Due	147,830	112,209
Current	11,757,577	10,966,140
Total loans	11,905,407	11,078,349
Recorded Investment > 90 Days and Accruing	2,367	11,203
Total Commercial [Member] | Total Commercial And Industrial [Member] | Commercial Non-Real Estate [Member]
Financing Receivable, Recorded Investment, Past Due [Line Items]
Total Past Due	135,144	93,703
Current	9,031,803	8,526,898
Total loans	9,166,947	8,620,601
Recorded Investment > 90 Days and Accruing	1,537	10,823
Total Commercial [Member] | Total Commercial And Industrial [Member] | Commercial Real Estate - Owner Occupied [Member]
Financing Receivable, Recorded Investment, Past Due [Line Items]
Total Past Due	12,686	18,506
Current	2,725,774	2,439,242
Total loans	2,738,460	2,457,748
Recorded Investment > 90 Days and Accruing	830	380
Total Commercial [Member] | Total Commercial And Industrial [Member] | 30-59 Days Past Due [Member]
Financing Receivable, Recorded Investment, Past Due [Line Items]
Total Past Due	25,755	14,651
Total Commercial [Member] | Total Commercial And Industrial [Member] | 30-59 Days Past Due [Member] | Commercial Non-Real Estate [Member]
Financing Receivable, Recorded Investment, Past Due [Line Items]
Total Past Due	20,893	12,257
Total Commercial [Member] | Total Commercial And Industrial [Member] | 30-59 Days Past Due [Member] | Commercial Real Estate - Owner Occupied [Member]
Financing Receivable, Recorded Investment, Past Due [Line Items]
Total Past Due	4,862	2,394
Total Commercial [Member] | Total Commercial And Industrial [Member] | 60-89 Days Past Due [Member]
Financing Receivable, Recorded Investment, Past Due [Line Items]
Total Past Due	14,001	5,465
Total Commercial [Member] | Total Commercial And Industrial [Member] | 60-89 Days Past Due [Member] | Commercial Non-Real Estate [Member]
Financing Receivable, Recorded Investment, Past Due [Line Items]
Total Past Due	13,445	3,895
Total Commercial [Member] | Total Commercial And Industrial [Member] | 60-89 Days Past Due [Member] | Commercial Real Estate - Owner Occupied [Member]
Financing Receivable, Recorded Investment, Past Due [Line Items]
Total Past Due	556	1,570
Total Commercial [Member] | Total Commercial And Industrial [Member] | Greater Than 90 Days Past Due [Member]
Financing Receivable, Recorded Investment, Past Due [Line Items]
Total Past Due	108,074	92,093
Total Commercial [Member] | Total Commercial And Industrial [Member] | Greater Than 90 Days Past Due [Member] | Commercial Non-Real Estate [Member]
Financing Receivable, Recorded Investment, Past Due [Line Items]
Total Past Due	100,806	77,551
Total Commercial [Member] | Total Commercial And Industrial [Member] | Greater Than 90 Days Past Due [Member] | Commercial Real Estate - Owner Occupied [Member]
Financing Receivable, Recorded Investment, Past Due [Line Items]
Total Past Due	7,268	14,542
Residential Mortgages [Member]
Financing Receivable, Recorded Investment, Past Due [Line Items]
Total Past Due	65,028	70,750
Current	2,925,603	2,839,331
Total loans	2,990,631	2,910,081
Recorded Investment > 90 Days and Accruing	85
Residential Mortgages [Member] | 30-59 Days Past Due [Member]
Financing Receivable, Recorded Investment, Past Due [Line Items]
Total Past Due	32,867	32,869
Residential Mortgages [Member] | 60-89 Days Past Due [Member]
Financing Receivable, Recorded Investment, Past Due [Line Items]
Total Past Due	8,584	14,706
Residential Mortgages [Member] | Greater Than 90 Days Past Due [Member]
Financing Receivable, Recorded Investment, Past Due [Line Items]
Total Past Due	23,577	23,175
Consumer [Member]
Financing Receivable, Recorded Investment, Past Due [Line Items]
Total Past Due	34,702	34,762
Current	2,130,116	2,113,105
Total loans	2,164,818	2,147,867
Recorded Investment > 90 Days and Accruing	1,638	618
Consumer [Member] | 30-59 Days Past Due [Member]
Financing Receivable, Recorded Investment, Past Due [Line Items]
Total Past Due	18,586	20,402
Consumer [Member] | 60-89 Days Past Due [Member]
Financing Receivable, Recorded Investment, Past Due [Line Items]
Total Past Due	6,215	4,695
Consumer [Member] | Greater Than 90 Days Past Due [Member]
Financing Receivable, Recorded Investment, Past Due [Line Items]
Total Past Due	$ 9,901	$ 9,665