Loans and Allowance for Loan Losses (Credit Quality Indicators by Segments and Portfolio Class) (Details) - USD ($) $ in Thousands	Sep. 30, 2016	Dec. 31, 2015	Sep. 30, 2015
Financing Receivable, Recorded Investment [Line Items]
Total loans	$ 16,070,821	$ 15,703,314	$ 14,763,050
Total Commercial [Member]
Financing Receivable, Recorded Investment [Line Items]
Total loans	11,972,654	11,560,325
Total Commercial [Member] | Pass [Member]
Financing Receivable, Recorded Investment [Line Items]
Total loans	10,401,630	10,577,368
Total Commercial [Member] | Pass-Watch [Member]
Financing Receivable, Recorded Investment [Line Items]
Total loans	314,912	221,911
Total Commercial [Member] | Special Mention [Member]
Financing Receivable, Recorded Investment [Line Items]
Total loans	234,752	270,579
Total Commercial [Member] | Substandard [Member]
Financing Receivable, Recorded Investment [Line Items]
Total loans	991,396	490,407
Total Commercial [Member] | Doubtful [Member]
Financing Receivable, Recorded Investment [Line Items]
Total loans	29,964	60
Residential Mortgages [Member]
Financing Receivable, Recorded Investment [Line Items]
Total loans	2,037,162	2,049,524	2,013,789
Consumer [Member]
Financing Receivable, Recorded Investment [Line Items]
Total loans	2,061,005	2,093,465	1,990,296
Residential Mortgages and Consumer [Member]
Financing Receivable, Recorded Investment [Line Items]
Total loans	4,098,167	4,142,989
Commercial Real Estate - Income Producing [Member] | Total Commercial [Member]
Financing Receivable, Recorded Investment [Line Items]
Total loans	1,990,309	1,553,082	1,484,232
Commercial Real Estate - Income Producing [Member] | Total Commercial [Member] | Pass [Member]
Financing Receivable, Recorded Investment [Line Items]
Total loans	1,876,423	1,502,484
Commercial Real Estate - Income Producing [Member] | Total Commercial [Member] | Pass-Watch [Member]
Financing Receivable, Recorded Investment [Line Items]
Total loans	69,773	14,717
Commercial Real Estate - Income Producing [Member] | Total Commercial [Member] | Special Mention [Member]
Financing Receivable, Recorded Investment [Line Items]
Total loans	6,100	5,905
Commercial Real Estate - Income Producing [Member] | Total Commercial [Member] | Substandard [Member]
Financing Receivable, Recorded Investment [Line Items]
Total loans	38,000	29,960
Commercial Real Estate - Income Producing [Member] | Total Commercial [Member] | Doubtful [Member]
Financing Receivable, Recorded Investment [Line Items]
Total loans	13	16
Construction and Land Development [Member] | Total Commercial [Member]
Financing Receivable, Recorded Investment [Line Items]
Total loans	946,592	1,151,950	1,085,585
Construction and Land Development [Member] | Total Commercial [Member] | Pass [Member]
Financing Receivable, Recorded Investment [Line Items]
Total loans	904,550	1,095,296
Construction and Land Development [Member] | Total Commercial [Member] | Pass-Watch [Member]
Financing Receivable, Recorded Investment [Line Items]
Total loans	21,945	6,841
Construction and Land Development [Member] | Total Commercial [Member] | Special Mention [Member]
Financing Receivable, Recorded Investment [Line Items]
Total loans	198	12,297
Construction and Land Development [Member] | Total Commercial [Member] | Substandard [Member]
Financing Receivable, Recorded Investment [Line Items]
Total loans	19,899	37,516
Total Commercial & Industrial [Member] | Total Commercial [Member]
Financing Receivable, Recorded Investment [Line Items]
Total loans	9,035,753	8,855,293	8,189,148
Total Commercial & Industrial [Member] | Total Commercial [Member] | Pass [Member]
Financing Receivable, Recorded Investment [Line Items]
Total loans	7,620,657	7,979,588
Total Commercial & Industrial [Member] | Total Commercial [Member] | Pass-Watch [Member]
Financing Receivable, Recorded Investment [Line Items]
Total loans	223,194	200,353
Total Commercial & Industrial [Member] | Total Commercial [Member] | Special Mention [Member]
Financing Receivable, Recorded Investment [Line Items]
Total loans	228,454	252,377
Total Commercial & Industrial [Member] | Total Commercial [Member] | Substandard [Member]
Financing Receivable, Recorded Investment [Line Items]
Total loans	933,497	422,931
Total Commercial & Industrial [Member] | Total Commercial [Member] | Doubtful [Member]
Financing Receivable, Recorded Investment [Line Items]
Total loans	29,951	44
Total Commercial & Industrial [Member] | Commercial Non-Real Estate [Member] | Total Commercial [Member]
Financing Receivable, Recorded Investment [Line Items]
Total loans	7,133,928	6,995,824	6,345,994
Total Commercial & Industrial [Member] | Commercial Non-Real Estate [Member] | Total Commercial [Member] | Pass [Member]
Financing Receivable, Recorded Investment [Line Items]
Total loans	5,899,626	6,260,863
Total Commercial & Industrial [Member] | Commercial Non-Real Estate [Member] | Total Commercial [Member] | Pass-Watch [Member]
Financing Receivable, Recorded Investment [Line Items]
Total loans	180,467	168,589
Total Commercial & Industrial [Member] | Commercial Non-Real Estate [Member] | Total Commercial [Member] | Special Mention [Member]
Financing Receivable, Recorded Investment [Line Items]
Total loans	196,408	211,230
Total Commercial & Industrial [Member] | Commercial Non-Real Estate [Member] | Total Commercial [Member] | Substandard [Member]
Financing Receivable, Recorded Investment [Line Items]
Total loans	827,476	355,098
Total Commercial & Industrial [Member] | Commercial Non-Real Estate [Member] | Total Commercial [Member] | Doubtful [Member]
Financing Receivable, Recorded Investment [Line Items]
Total loans	29,951	44
Total Commercial & Industrial [Member] | Commercial Real Estate - Owner Occupied [Member] | Total Commercial [Member]
Financing Receivable, Recorded Investment [Line Items]
Total loans	1,901,825	1,859,469	$ 1,843,154
Total Commercial & Industrial [Member] | Commercial Real Estate - Owner Occupied [Member] | Total Commercial [Member] | Pass [Member]
Financing Receivable, Recorded Investment [Line Items]
Total loans	1,721,031	1,718,725
Total Commercial & Industrial [Member] | Commercial Real Estate - Owner Occupied [Member] | Total Commercial [Member] | Pass-Watch [Member]
Financing Receivable, Recorded Investment [Line Items]
Total loans	42,727	31,764
Total Commercial & Industrial [Member] | Commercial Real Estate - Owner Occupied [Member] | Total Commercial [Member] | Special Mention [Member]
Financing Receivable, Recorded Investment [Line Items]
Total loans	32,046	41,147
Total Commercial & Industrial [Member] | Commercial Real Estate - Owner Occupied [Member] | Total Commercial [Member] | Substandard [Member]
Financing Receivable, Recorded Investment [Line Items]
Total loans	106,021	67,833
Performing [Member] | Residential Mortgages [Member]
Financing Receivable, Recorded Investment [Line Items]
Total loans	2,015,981	2,025,563
Performing [Member] | Consumer [Member]
Financing Receivable, Recorded Investment [Line Items]
Total loans	2,048,364	2,082,238
Performing [Member] | Residential Mortgages and Consumer [Member]
Financing Receivable, Recorded Investment [Line Items]
Total loans	4,064,345	4,107,801
Nonperforming [Member] | Residential Mortgages [Member]
Financing Receivable, Recorded Investment [Line Items]
Total loans	21,181	23,961
Nonperforming [Member] | Consumer [Member]
Financing Receivable, Recorded Investment [Line Items]
Total loans	12,641	11,227
Nonperforming [Member] | Residential Mortgages and Consumer [Member]
Financing Receivable, Recorded Investment [Line Items]
Total loans	$ 33,822	$ 35,188