Loans and Allowance for Loan Losses (Age Analysis of Past Due Loans by Portfolio Class) (Details) - USD ($) $ in Thousands	Sep. 30, 2016	Dec. 31, 2015	Sep. 30, 2015
Financing Receivable, Recorded Investment, Past Due [Line Items]
Total past due	$ 201,790	$ 153,691
Current	15,869,031	15,549,623
Total loans	16,070,821	15,703,314	$ 14,763,050
Recorded investment > 90 days and still accruing	4,933	7,653
30-59 Days Past Due [Member]
Financing Receivable, Recorded Investment, Past Due [Line Items]
Total past due	60,166	79,027
60-89 Days Past Due [Member]
Financing Receivable, Recorded Investment, Past Due [Line Items]
Total past due	39,644	12,101
Greater Than 90 Days Past Due [Member]
Financing Receivable, Recorded Investment, Past Due [Line Items]
Total past due	101,980	62,563
Total Commercial [Member]
Financing Receivable, Recorded Investment, Past Due [Line Items]
Total loans	11,972,654	11,560,325
Total Commercial [Member] | Commercial Real Estate - Income Producing [Member]
Financing Receivable, Recorded Investment, Past Due [Line Items]
Total past due	6,519	7,856
Current	1,983,790	1,545,226
Total loans	1,990,309	1,553,082	1,484,232
Recorded investment > 90 days and still accruing		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	1,873	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	225	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	4,421	6,382
Total Commercial [Member] | Construction and Land Development [Member]
Financing Receivable, Recorded Investment, Past Due [Line Items]
Total past due	9,992	24,365
Current	936,600	1,127,585
Total loans	946,592	1,151,950	1,085,585
Recorded investment > 90 days and still accruing	3,501	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	1,069	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	1,565	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	7,358	4,043
Total Commercial [Member] | Total Commercial & Industrial [Member]
Financing Receivable, Recorded Investment, Past Due [Line Items]
Total past due	115,239	57,227
Current	8,920,514	8,798,066
Total loans	9,035,753	8,855,293	8,189,148
Recorded investment > 90 days and still accruing	543	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	18,507	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	25,681	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	71,051	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	103,861	43,881
Current	7,030,067	6,951,943
Total loans	7,133,928	6,995,824	6,345,994
Recorded investment > 90 days and still accruing	543	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	15,501	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	24,566	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	63,794	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	11,378	13,346
Current	1,890,447	1,846,123
Total loans	1,901,825	1,859,469	1,843,154
Recorded investment > 90 days and still accruing		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	3,006	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	1,115	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	7,257	6,646
Residential Mortgages [Member]
Financing Receivable, Recorded Investment, Past Due [Line Items]
Total past due	41,379	34,857
Current	1,995,783	2,014,667
Total loans	2,037,162	2,049,524	2,013,789
Recorded investment > 90 days and still accruing		163
Residential Mortgages [Member] | 30-59 Days Past Due [Member]
Financing Receivable, Recorded Investment, Past Due [Line Items]
Total past due	23,067	18,657
Residential Mortgages [Member] | 60-89 Days Past Due [Member]
Financing Receivable, Recorded Investment, Past Due [Line Items]
Total past due	6,771	4,360
Residential Mortgages [Member] | Greater Than 90 Days Past Due [Member]
Financing Receivable, Recorded Investment, Past Due [Line Items]
Total past due	11,541	11,840
Consumer [Member]
Financing Receivable, Recorded Investment, Past Due [Line Items]
Total past due	28,661	29,386
Current	2,032,344	2,064,079
Total loans	2,061,005	2,093,465	$ 1,990,296
Recorded investment > 90 days and still accruing	889	2,166
Consumer [Member] | 30-59 Days Past Due [Member]
Financing Receivable, Recorded Investment, Past Due [Line Items]
Total past due	15,650	16,309
Consumer [Member] | 60-89 Days Past Due [Member]
Financing Receivable, Recorded Investment, Past Due [Line Items]
Total past due	5,402	4,432
Consumer [Member] | Greater Than 90 Days Past Due [Member]
Financing Receivable, Recorded Investment, Past Due [Line Items]
Total past due	$ 7,609	$ 8,645