Loans and Allowance for Loan Losses (Age Analysis of Past Due Loans by Portfolio Class) (Details) - USD ($) $ in Thousands	Jun. 30, 2017	Dec. 31, 2016	Jun. 30, 2016
Financing Receivable, Recorded Investment, Past Due [Line Items]
Total past due	$ 268,267	$ 195,107
Current	18,205,574	16,557,044
Total loans	18,473,841	16,752,151	$ 16,035,796
Recorded investment > 90 days and accruing	18,390	3,039
30-59 Days Past Due [Member]
Financing Receivable, Recorded Investment, Past Due [Line Items]
Total past due	83,099	67,482
60-89 Days Past Due [Member]
Financing Receivable, Recorded Investment, Past Due [Line Items]
Total past due	50,152	18,968
Greater Than 90 Days Past Due [Member]
Financing Receivable, Recorded Investment, Past Due [Line Items]
Total past due	135,016	108,657
Total Commercial [Member]
Financing Receivable, Recorded Investment, Past Due [Line Items]
Total loans	13,886,631	12,545,507
Total Commercial [Member] | Commercial Real Estate - Income Producing [Member]
Financing Receivable, Recorded Investment, Past Due [Line Items]
Total past due	10,728	5,914
Current	2,390,945	2,007,976
Total loans	2,401,673	2,013,890	2,024,471
Recorded investment > 90 days and accruing	1,989	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	3,369	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	2,319	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	5,040	5,026
Total Commercial [Member] | Construction and Land Development [Member]
Financing Receivable, Recorded Investment, Past Due [Line Items]
Total past due	8,849	6,165
Current	1,304,673	1,004,714
Total loans	1,313,522	1,010,879	880,588
Recorded investment > 90 days and accruing		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	6,250	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	619	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	1,980	5,300
Total Commercial [Member] | Total Commercial & Industrial [Member]
Financing Receivable, Recorded Investment, Past Due [Line Items]
Total past due	159,754	100,035
Current	10,011,682	9,420,703
Total loans	10,171,436	9,520,738	9,048,719
Recorded investment > 90 days and accruing	13,512	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	32,283	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	29,163	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	98,308	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	147,712	90,136
Current	7,945,392	7,523,781
Total loans	8,093,104	7,613,917	7,132,519
Recorded investment > 90 days and accruing	13,088	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	27,751	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	27,974	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	91,987	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	12,042	9,899
Current	2,066,290	1,896,922
Total loans	2,078,332	1,906,821	1,916,200
Recorded investment > 90 days and accruing	424	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	4,532	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	1,189	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	6,321	6,310
Residential Mortgages [Member]
Financing Receivable, Recorded Investment, Past Due [Line Items]
Total past due	59,729	47,784
Current	2,434,194	2,098,929
Total loans	2,493,923	2,146,713	2,017,650
Recorded investment > 90 days and accruing	2,801	1
Residential Mortgages [Member] | 30-59 Days Past Due [Member]
Financing Receivable, Recorded Investment, Past Due [Line Items]
Total past due	25,433	24,599
Residential Mortgages [Member] | 60-89 Days Past Due [Member]
Financing Receivable, Recorded Investment, Past Due [Line Items]
Total past due	12,208	8,816
Residential Mortgages [Member] | Greater Than 90 Days Past Due [Member]
Financing Receivable, Recorded Investment, Past Due [Line Items]
Total past due	22,088	14,369
Consumer [Member]
Financing Receivable, Recorded Investment, Past Due [Line Items]
Total past due	29,207	35,209
Current	2,064,080	2,024,722
Total loans	2,093,287	2,059,931	$ 2,064,368
Recorded investment > 90 days and accruing	88	823
Consumer [Member] | 30-59 Days Past Due [Member]
Financing Receivable, Recorded Investment, Past Due [Line Items]
Total past due	15,764	18,621
Consumer [Member] | 60-89 Days Past Due [Member]
Financing Receivable, Recorded Investment, Past Due [Line Items]
Total past due	5,843	7,441
Consumer [Member] | Greater Than 90 Days Past Due [Member]
Financing Receivable, Recorded Investment, Past Due [Line Items]
Total past due	$ 7,600	$ 9,147