Loans and Allowance for Loan Losses (Age Analysis of Past Due Loans by Portfolio Class) (Details) - USD ($) $ in Thousands	Mar. 31, 2019	Dec. 31, 2018	Mar. 31, 2018
Financing Receivable, Recorded Investment, Past Due [Line Items]
Total Past Due	$ 230,462	$ 237,050
Current	19,882,376	19,789,361
Total loans	20,112,838	20,026,411	$ 19,092,504
Recorded Investment > 90 Days and Accruing	21,793	14,309
30-59 Days Past Due [Member]
Financing Receivable, Recorded Investment, Past Due [Line Items]
Total Past Due	93,303	77,690
60-89 Days Past Due [Member]
Financing Receivable, Recorded Investment, Past Due [Line Items]
Total Past Due	15,439	26,767
Greater Than 90 Days Past Due [Member]
Financing Receivable, Recorded Investment, Past Due [Line Items]
Total Past Due	121,720	132,593
Total Commercial [Member] | Commercial Real Estate - Income Producing [Member]
Financing Receivable, Recorded Investment, Past Due [Line Items]
Total Past Due	11,978	8,638
Current	2,551,416	2,333,141
Total loans	2,563,394	2,341,779	2,394,862
Recorded Investment > 90 Days and Accruing	1,876	1,844
Total Commercial [Member] | Commercial Real Estate - Income Producing [Member] | 30-59 Days Past Due [Member]
Financing Receivable, Recorded Investment, Past Due [Line Items]
Total Past Due	6,124	2,371
Total Commercial [Member] | Commercial Real Estate - Income Producing [Member] | 60-89 Days Past Due [Member]
Financing Receivable, Recorded Investment, Past Due [Line Items]
Total Past Due		772
Total Commercial [Member] | Commercial Real Estate - Income Producing [Member] | Greater Than 90 Days Past Due [Member]
Financing Receivable, Recorded Investment, Past Due [Line Items]
Total Past Due	5,854	5,495
Total Commercial [Member] | Construction and Land Development [Member]
Financing Receivable, Recorded Investment, Past Due [Line Items]
Total Past Due	10,271	10,691
Current	1,329,796	1,537,644
Total loans	1,340,067	1,548,335	1,413,878
Recorded Investment > 90 Days and Accruing	721	644
Total Commercial [Member] | Construction and Land Development [Member] | 30-59 Days Past Due [Member]
Financing Receivable, Recorded Investment, Past Due [Line Items]
Total Past Due	8,328	7,397
Total Commercial [Member] | Construction and Land Development [Member] | 60-89 Days Past Due [Member]
Financing Receivable, Recorded Investment, Past Due [Line Items]
Total Past Due	186	1,129
Total Commercial [Member] | Construction and Land Development [Member] | Greater Than 90 Days Past Due [Member]
Financing Receivable, Recorded Investment, Past Due [Line Items]
Total Past Due	1,757	2,165
Total Commercial [Member] | Total Commercial And Industrial [Member]
Financing Receivable, Recorded Investment, Past Due [Line Items]
Total Past Due	112,252	112,209
Current	11,059,502	10,966,140
Total loans	11,171,754	11,078,349	10,521,765
Recorded Investment > 90 Days and Accruing	17,857	11,203
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	23,579	14,651
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	3,088	5,465
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	85,585	92,093
Total Commercial [Member] | Total Commercial And Industrial [Member] | Commercial Non-Real Estate [Member]
Financing Receivable, Recorded Investment, Past Due [Line Items]
Total Past Due	90,812	93,703
Current	8,565,514	8,526,898
Total loans	8,656,326	8,620,601	8,336,222
Recorded Investment > 90 Days and Accruing	13,920	10,823
Total Commercial [Member] | Total Commercial And Industrial [Member] | Commercial Non-Real Estate [Member] | 30-59 Days Past Due [Member]
Financing Receivable, Recorded Investment, Past Due [Line Items]
Total Past Due	19,036	12,257
Total Commercial [Member] | Total Commercial And Industrial [Member] | Commercial Non-Real Estate [Member] | 60-89 Days Past Due [Member]
Financing Receivable, Recorded Investment, Past Due [Line Items]
Total Past Due	2,527	3,895
Total Commercial [Member] | Total Commercial And Industrial [Member] | Commercial Non-Real Estate [Member] | Greater Than 90 Days Past Due [Member]
Financing Receivable, Recorded Investment, Past Due [Line Items]
Total Past Due	69,249	77,551
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	21,440	18,506
Current	2,493,988	2,439,242
Total loans	2,515,428	2,457,748	2,185,543
Recorded Investment > 90 Days and Accruing	3,937	380
Total Commercial [Member] | Total Commercial And Industrial [Member] | Commercial Real Estate - Owner Occupied [Member] | 30-59 Days Past Due [Member]
Financing Receivable, Recorded Investment, Past Due [Line Items]
Total Past Due	4,543	2,394
Total Commercial [Member] | Total Commercial And Industrial [Member] | Commercial Real Estate - Owner Occupied [Member] | 60-89 Days Past Due [Member]
Financing Receivable, Recorded Investment, Past Due [Line Items]
Total Past Due	561	1,570
Total Commercial [Member] | Total Commercial And Industrial [Member] | Commercial Real Estate - Owner Occupied [Member] | Greater Than 90 Days Past Due [Member]
Financing Receivable, Recorded Investment, Past Due [Line Items]
Total Past Due	16,336	14,542
Residential Mortgages [Member]
Financing Receivable, Recorded Investment, Past Due [Line Items]
Total Past Due	66,878	70,750
Current	2,866,373	2,839,331
Total loans	2,933,251	2,910,081	2,732,821
Recorded Investment > 90 Days and Accruing	679
Residential Mortgages [Member] | 30-59 Days Past Due [Member]
Financing Receivable, Recorded Investment, Past Due [Line Items]
Total Past Due	39,534	32,869
Residential Mortgages [Member] | 60-89 Days Past Due [Member]
Financing Receivable, Recorded Investment, Past Due [Line Items]
Total Past Due	8,045	14,706
Residential Mortgages [Member] | Greater Than 90 Days Past Due [Member]
Financing Receivable, Recorded Investment, Past Due [Line Items]
Total Past Due	19,299	23,175
Consumer [Member]
Financing Receivable, Recorded Investment, Past Due [Line Items]
Total Past Due	29,083	34,762
Current	2,075,289	2,113,105
Total loans	2,104,372	2,147,867	$ 2,029,178
Recorded Investment > 90 Days and Accruing	660	618
Consumer [Member] | 30-59 Days Past Due [Member]
Financing Receivable, Recorded Investment, Past Due [Line Items]
Total Past Due	15,738	20,402
Consumer [Member] | 60-89 Days Past Due [Member]
Financing Receivable, Recorded Investment, Past Due [Line Items]
Total Past Due	4,120	4,695
Consumer [Member] | Greater Than 90 Days Past Due [Member]
Financing Receivable, Recorded Investment, Past Due [Line Items]
Total Past Due	$ 9,225	$ 9,665