Loans and Allowance for Loan Losses (Age Analysis of Past Due Loans by Portfolio Class) (Details) - USD ($) $ in Thousands	Sep. 30, 2017	Dec. 31, 2016	Sep. 30, 2016
Financing Receivable, Recorded Investment, Past Due [Line Items]
Total past due	$ 292,318	$ 195,107
Current	18,493,967	16,557,044
Total loans	18,786,285	16,752,151	$ 16,070,821
Recorded investment > 90 days and still accruing	28,850	3,039
30-59 Days Past Due [Member]
Financing Receivable, Recorded Investment, Past Due [Line Items]
Total past due	111,426	67,482
60-89 Days Past Due [Member]
Financing Receivable, Recorded Investment, Past Due [Line Items]
Total past due	26,946	18,968
Greater Than 90 Days Past Due [Member]
Financing Receivable, Recorded Investment, Past Due [Line Items]
Total past due	153,946	108,657
Total Commercial [Member]
Financing Receivable, Recorded Investment, Past Due [Line Items]
Total loans	14,090,299	12,545,507
Total Commercial [Member] | Commercial Real Estate - Income Producing [Member]
Financing Receivable, Recorded Investment, Past Due [Line Items]
Total past due	10,947	5,914
Current	2,500,861	2,007,976
Total loans	2,511,808	2,013,890	1,990,309
Recorded investment > 90 days and still accruing	2,907	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	1,540	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	3,731	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	5,676	5,026
Total Commercial [Member] | Construction and Land Development [Member]
Financing Receivable, Recorded Investment, Past Due [Line Items]
Total past due	8,910	6,165
Current	1,364,138	1,004,714
Total loans	1,373,048	1,010,879	946,592
Recorded investment > 90 days and still accruing	417	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	5,018	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	1,031	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	2,861	5,300
Total Commercial [Member] | Total Commercial & Industrial [Member]
Financing Receivable, Recorded Investment, Past Due [Line Items]
Total past due	167,680	100,035
Current	10,037,763	9,420,703
Total loans	10,205,443	9,520,738	9,035,753
Recorded investment > 90 days and still accruing	25,167	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	50,213	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	4,183	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	113,284	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	139,848	90,136
Current	7,989,581	7,523,781
Total loans	8,129,429	7,613,917	7,133,928
Recorded investment > 90 days and still accruing	24,400	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	31,634	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	3,880	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	104,334	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	27,832	9,899
Current	2,048,182	1,896,922
Total loans	2,076,014	1,906,821	1,901,825
Recorded investment > 90 days and still accruing	767	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	18,579	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	303	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	8,950	6,310
Residential Mortgages [Member]
Financing Receivable, Recorded Investment, Past Due [Line Items]
Total past due	74,071	47,784
Current	2,522,621	2,098,929
Total loans	2,596,692	2,146,713	2,037,162
Recorded investment > 90 days and still accruing	41	1
Residential Mortgages [Member] | 30-59 Days Past Due [Member]
Financing Receivable, Recorded Investment, Past Due [Line Items]
Total past due	39,081	24,599
Residential Mortgages [Member] | 60-89 Days Past Due [Member]
Financing Receivable, Recorded Investment, Past Due [Line Items]
Total past due	10,575	8,816
Residential Mortgages [Member] | Greater Than 90 Days Past Due [Member]
Financing Receivable, Recorded Investment, Past Due [Line Items]
Total past due	24,415	14,369
Consumer [Member]
Financing Receivable, Recorded Investment, Past Due [Line Items]
Total past due	30,710	35,209
Current	2,068,584	2,024,722
Total loans	2,099,294	2,059,931	$ 2,061,005
Recorded investment > 90 days and still accruing	318	823
Consumer [Member] | 30-59 Days Past Due [Member]
Financing Receivable, Recorded Investment, Past Due [Line Items]
Total past due	15,574	18,621
Consumer [Member] | 60-89 Days Past Due [Member]
Financing Receivable, Recorded Investment, Past Due [Line Items]
Total past due	7,426	7,441
Consumer [Member] | Greater Than 90 Days Past Due [Member]
Financing Receivable, Recorded Investment, Past Due [Line Items]
Total past due	$ 7,710	$ 9,147