Loans and Allowance for Loan Losses (Age Analysis of Past Due Loans by Portfolio Class) (Details) - USD ($) $ in Thousands	Mar. 31, 2017	Dec. 31, 2016	Mar. 31, 2016
Financing Receivable, Recorded Investment, Past Due [Line Items]
Total past due	$ 237,535	$ 195,107
Current	17,967,333	16,557,044
Total loans	18,204,868	16,752,151	$ 15,978,124
Recorded investment > 90 days and accruing	590	3,039
30-59 Days Past Due [Member]
Financing Receivable, Recorded Investment, Past Due [Line Items]
Total past due	110,344	67,482
60-89 Days Past Due [Member]
Financing Receivable, Recorded Investment, Past Due [Line Items]
Total past due	29,928	18,968
Greater Than 90 Days Past Due [Member]
Financing Receivable, Recorded Investment, Past Due [Line Items]
Total past due	97,263	108,657
Total Commercial [Member]
Financing Receivable, Recorded Investment, Past Due [Line Items]
Total loans	13,879,509	12,545,507
Total Commercial [Member] | Commercial Real Estate - Income Producing [Member]
Financing Receivable, Recorded Investment, Past Due [Line Items]
Total past due	10,867	5,914
Current	2,494,237	2,007,976
Total loans	2,505,104	2,013,890	1,752,745
Recorded investment > 90 days and accruing	185	216
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	4,365	838
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	1,688	50
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	4,814	5,026
Total Commercial [Member] | Construction and Land Development [Member]
Financing Receivable, Recorded Investment, Past Due [Line Items]
Total past due	18,132	6,165
Current	1,234,535	1,004,714
Total loans	1,252,667	1,010,879	1,095,414
Recorded investment > 90 days and accruing	25	1,563
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	14,845	694
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	343	171
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	2,944	5,300
Total Commercial [Member] | Total Commercial & Industrial [Member]
Financing Receivable, Recorded Investment, Past Due [Line Items]
Total past due	139,954	100,035
Current	9,981,784	9,420,703
Total loans	10,121,738	9,520,738	9,068,753
Recorded investment > 90 days and accruing	280	436
Total Commercial [Member] | Total Commercial & Industrial [Member] | 30-59 Days Past Due [Member]
Financing Receivable, Recorded Investment, Past Due [Line Items]
Total past due	56,584	22,730
Total Commercial [Member] | Total Commercial & Industrial [Member] | 60-89 Days Past Due [Member]
Financing Receivable, Recorded Investment, Past Due [Line Items]
Total past due	17,256	2,490
Total Commercial [Member] | Total Commercial & Industrial [Member] | Greater Than 90 Days Past Due [Member]
Financing Receivable, Recorded Investment, Past Due [Line Items]
Total past due	66,114	74,815
Total Commercial [Member] | Total Commercial & Industrial [Member] | Commercial Non-Real Estate [Member]
Financing Receivable, Recorded Investment, Past Due [Line Items]
Total past due	128,743	90,136
Current	7,945,544	7,523,781
Total loans	8,074,287	7,613,917	7,145,406
Recorded investment > 90 days and accruing	245	384
Total Commercial [Member] | Total Commercial & Industrial [Member] | Commercial Non-Real Estate [Member] | 30-59 Days Past Due [Member]
Financing Receivable, Recorded Investment, Past Due [Line Items]
Total past due	52,677	19,722
Total Commercial [Member] | Total Commercial & Industrial [Member] | Commercial Non-Real Estate [Member] | 60-89 Days Past Due [Member]
Financing Receivable, Recorded Investment, Past Due [Line Items]
Total past due	15,530	1,909
Total Commercial [Member] | Total Commercial & 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	60,536	68,505
Total Commercial [Member] | Total Commercial & Industrial [Member] | Commercial Real Estate - Owner Occupied [Member]
Financing Receivable, Recorded Investment, Past Due [Line Items]
Total past due	11,211	9,899
Current	2,036,240	1,896,922
Total loans	2,047,451	1,906,821	1,923,347
Recorded investment > 90 days and accruing	35	52
Total Commercial [Member] | Total Commercial & 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	3,907	3,008
Total Commercial [Member] | Total Commercial & 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	1,726	581
Total Commercial [Member] | Total Commercial & 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	5,578	6,310
Residential Mortgages [Member]
Financing Receivable, Recorded Investment, Past Due [Line Items]
Total past due	38,863	47,784
Current	2,227,400	2,098,929
Total loans	2,266,263	2,146,713	2,000,967
Recorded investment > 90 days and accruing		1
Residential Mortgages [Member] | 30-59 Days Past Due [Member]
Financing Receivable, Recorded Investment, Past Due [Line Items]
Total past due	18,104	24,599
Residential Mortgages [Member] | 60-89 Days Past Due [Member]
Financing Receivable, Recorded Investment, Past Due [Line Items]
Total past due	5,104	8,816
Residential Mortgages [Member] | Greater Than 90 Days Past Due [Member]
Financing Receivable, Recorded Investment, Past Due [Line Items]
Total past due	15,655	14,369
Consumer [Member]
Financing Receivable, Recorded Investment, Past Due [Line Items]
Total past due	29,719	35,209
Current	2,029,377	2,024,722
Total loans	2,059,096	2,059,931	$ 2,060,245
Recorded investment > 90 days and accruing	100	823
Consumer [Member] | 30-59 Days Past Due [Member]
Financing Receivable, Recorded Investment, Past Due [Line Items]
Total past due	16,446	18,621
Consumer [Member] | 60-89 Days Past Due [Member]
Financing Receivable, Recorded Investment, Past Due [Line Items]
Total past due	5,537	7,441
Consumer [Member] | Greater Than 90 Days Past Due [Member]
Financing Receivable, Recorded Investment, Past Due [Line Items]
Total past due	$ 7,736	$ 9,147