Loans and Allowance for Loan Losses (Age Analysis of Past Due Loans by Portfolio Class) (Details) - USD ($) $ in Thousands	Jun. 30, 2016	Dec. 31, 2015	Jun. 30, 2015
Financing Receivable, Recorded Investment, Past Due [Line Items]
Total past due	$ 190,482	$ 153,691
Current	15,845,314	15,549,623
Total loans	16,035,796	15,703,314	$ 14,344,752
Recorded investment > 90 days and still accruing	7,982	7,653
30-59 Days Past Due [Member]
Financing Receivable, Recorded Investment, Past Due [Line Items]
Total past due	81,399	79,027
60-89 Days Past Due [Member]
Financing Receivable, Recorded Investment, Past Due [Line Items]
Total past due	43,854	12,101
Greater Than 90 Days Past Due [Member]
Financing Receivable, Recorded Investment, Past Due [Line Items]
Total past due	65,229	62,563
Total Commercial [Member]
Financing Receivable, Recorded Investment, Past Due [Line Items]
Total loans	11,953,778	11,560,325
Total Commercial [Member] | Commercial Real Estate - Income Producing [Member]
Financing Receivable, Recorded Investment, Past Due [Line Items]
Total past due	5,827	7,856
Current	2,018,644	1,545,226
Total loans	2,024,471	1,553,082	1,452,091
Recorded investment > 90 days and still accruing	194	499
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	2,583	871
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	467	603
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	2,777	6,382
Total Commercial [Member] | Construction and Land Development [Member]
Financing Receivable, Recorded Investment, Past Due [Line Items]
Total past due	9,971	24,365
Current	870,617	1,127,585
Total loans	880,588	1,151,950	1,120,947
Recorded investment > 90 days and still accruing	4,759	1,230
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	1,386	19,886
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	938	436
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	7,647	4,043
Total Commercial [Member] | Total Commercial & Industrial [Member]
Financing Receivable, Recorded Investment, Past Due [Line Items]
Total past due	117,156	57,227
Current	8,931,563	8,798,066
Total loans	9,048,719	8,855,293	7,946,426
Recorded investment > 90 days and still accruing	2,062	3,595
Total Commercial [Member] | Total Commercial & Industrial [Member] | 30-59 Days Past Due [Member]
Financing Receivable, Recorded Investment, Past Due [Line Items]
Total past due	50,310	23,304
Total Commercial [Member] | Total Commercial & Industrial [Member] | 60-89 Days Past Due [Member]
Financing Receivable, Recorded Investment, Past Due [Line Items]
Total past due	30,697	2,270
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	36,149	31,653
Total Commercial [Member] | Total Commercial & Industrial [Member] | Commercial Non-Real Estate [Member]
Financing Receivable, Recorded Investment, Past Due [Line Items]
Total past due	105,450	43,881
Current	7,027,069	6,951,943
Total loans	7,132,519	6,995,824	6,185,684
Recorded investment > 90 days and still accruing	567	3,060
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	47,859	17,406
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	28,591	1,468
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	29,000	25,007
Total Commercial [Member] | Total Commercial & Industrial [Member] | Commercial Real Estate - Owner Occupied [Member]
Financing Receivable, Recorded Investment, Past Due [Line Items]
Total past due	11,706	13,346
Current	1,904,494	1,846,123
Total loans	1,916,200	1,859,469	1,760,742
Recorded investment > 90 days and still accruing	1,495	535
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	2,451	5,898
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	2,106	802
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	7,149	6,646
Residential Mortgages [Member]
Financing Receivable, Recorded Investment, Past Due [Line Items]
Total past due	34,950	34,857
Current	1,982,700	2,014,667
Total loans	2,017,650	2,049,524	1,955,837
Recorded investment > 90 days and still accruing	143	163
Residential Mortgages [Member] | 30-59 Days Past Due [Member]
Financing Receivable, Recorded Investment, Past Due [Line Items]
Total past due	15,108	18,657
Residential Mortgages [Member] | 60-89 Days Past Due [Member]
Financing Receivable, Recorded Investment, Past Due [Line Items]
Total past due	7,293	4,360
Residential Mortgages [Member] | Greater Than 90 Days Past Due [Member]
Financing Receivable, Recorded Investment, Past Due [Line Items]
Total past due	12,549	11,840
Consumer [Member]
Financing Receivable, Recorded Investment, Past Due [Line Items]
Total past due	22,578	29,386
Current	2,041,790	2,064,079
Total loans	2,064,368	2,093,465	$ 1,869,451
Recorded investment > 90 days and still accruing	824	2,166
Consumer [Member] | 30-59 Days Past Due [Member]
Financing Receivable, Recorded Investment, Past Due [Line Items]
Total past due	12,012	16,309
Consumer [Member] | 60-89 Days Past Due [Member]
Financing Receivable, Recorded Investment, Past Due [Line Items]
Total past due	4,459	4,432
Consumer [Member] | Greater Than 90 Days Past Due [Member]
Financing Receivable, Recorded Investment, Past Due [Line Items]
Total past due	$ 6,107	$ 8,645