Loans and Allowance for Loan Losses (Credit Quality Indicators by Segments and Portfolio Class) (Details) - USD ($) $ in Thousands	Dec. 31, 2017	Dec. 31, 2016
Total Commercial [Member]
Financing Receivable, Recorded Investment [Line Items]
Total loans	$ 14,198,396	$ 12,545,507
Total Commercial [Member] | Pass [Member]
Financing Receivable, Recorded Investment [Line Items]
Total loans	12,601,853	10,925,611
Total Commercial [Member] | Pass-Watch [Member]
Financing Receivable, Recorded Investment [Line Items]
Total loans	520,230	351,888
Total Commercial [Member] | Special Mention [Member]
Financing Receivable, Recorded Investment [Line Items]
Total loans	126,137	248,696
Total Commercial [Member] | Substandard [Member]
Financing Receivable, Recorded Investment [Line Items]
Total loans	950,111	1,001,599
Total Commercial [Member] | Doubtful [Member]
Financing Receivable, Recorded Investment [Line Items]
Total loans	65	17,713
Residential Mortgages [Member]
Financing Receivable, Recorded Investment [Line Items]
Total loans	2,690,472	2,146,713
Consumer [Member]
Financing Receivable, Recorded Investment [Line Items]
Total loans	2,115,295	2,059,931
Residential Mortgage and Consumer [Member]
Financing Receivable, Recorded Investment [Line Items]
Total loans	4,805,767	4,206,644
Commercial Real Estate - Income Producing [Member] | Total Commercial [Member]
Financing Receivable, Recorded Investment [Line Items]
Total loans	2,384,599	2,013,890
Commercial Real Estate - Income Producing [Member] | Total Commercial [Member] | Pass [Member]
Financing Receivable, Recorded Investment [Line Items]
Total loans	2,223,245	1,873,644
Commercial Real Estate - Income Producing [Member] | Total Commercial [Member] | Pass-Watch [Member]
Financing Receivable, Recorded Investment [Line Items]
Total loans	83,444	78,309
Commercial Real Estate - Income Producing [Member] | Total Commercial [Member] | Special Mention [Member]
Financing Receivable, Recorded Investment [Line Items]
Total loans	13,244	22,492
Commercial Real Estate - Income Producing [Member] | Total Commercial [Member] | Substandard [Member]
Financing Receivable, Recorded Investment [Line Items]
Total loans	64,658	39,434
Commercial Real Estate - Income Producing [Member] | Total Commercial [Member] | Doubtful [Member]
Financing Receivable, Recorded Investment [Line Items]
Total loans	8	11
Construction and Land Development [Member] | Total Commercial [Member]
Financing Receivable, Recorded Investment [Line Items]
Total loans	1,373,421	1,010,879
Construction and Land Development [Member] | Total Commercial [Member] | Pass [Member]
Financing Receivable, Recorded Investment [Line Items]
Total loans	1,291,638	968,505
Construction and Land Development [Member] | Total Commercial [Member] | Pass-Watch [Member]
Financing Receivable, Recorded Investment [Line Items]
Total loans	60,804	22,592
Construction and Land Development [Member] | Total Commercial [Member] | Special Mention [Member]
Financing Receivable, Recorded Investment [Line Items]
Total loans	4,788	4,142
Construction and Land Development [Member] | Total Commercial [Member] | Substandard [Member]
Financing Receivable, Recorded Investment [Line Items]
Total loans	16,191	15,640
Total Commercial And Industrial [Member] | Total Commercial [Member]
Financing Receivable, Recorded Investment [Line Items]
Total loans	10,440,376	9,520,738
Total Commercial And Industrial [Member] | Total Commercial [Member] | Pass [Member]
Financing Receivable, Recorded Investment [Line Items]
Total loans	9,086,970	8,083,462
Total Commercial And Industrial [Member] | Total Commercial [Member] | Pass-Watch [Member]
Financing Receivable, Recorded Investment [Line Items]
Total loans	375,982	250,987
Total Commercial And Industrial [Member] | Total Commercial [Member] | Special Mention [Member]
Financing Receivable, Recorded Investment [Line Items]
Total loans	108,105	222,062
Total Commercial And Industrial [Member] | Total Commercial [Member] | Substandard [Member]
Financing Receivable, Recorded Investment [Line Items]
Total loans	869,262	946,525
Total Commercial And Industrial [Member] | Total Commercial [Member] | Doubtful [Member]
Financing Receivable, Recorded Investment [Line Items]
Total loans	57	17,702
Total Commercial And Industrial [Member] | Commercial Non-Real Estate [Member] | Total Commercial [Member]
Financing Receivable, Recorded Investment [Line Items]
Total loans	8,297,937	7,613,917
Total Commercial And Industrial [Member] | Commercial Non-Real Estate [Member] | Total Commercial [Member] | Pass [Member]
Financing Receivable, Recorded Investment [Line Items]
Total loans	7,190,604	6,364,348
Total Commercial And Industrial [Member] | Commercial Non-Real Estate [Member] | Total Commercial [Member] | Pass-Watch [Member]
Financing Receivable, Recorded Investment [Line Items]
Total loans	293,069	203,311
Total Commercial And Industrial [Member] | Commercial Non-Real Estate [Member] | Total Commercial [Member] | Special Mention [Member]
Financing Receivable, Recorded Investment [Line Items]
Total loans	80,649	181,763
Total Commercial And Industrial [Member] | Commercial Non-Real Estate [Member] | Total Commercial [Member] | Substandard [Member]
Financing Receivable, Recorded Investment [Line Items]
Total loans	733,558	846,793
Total Commercial And Industrial [Member] | Commercial Non-Real Estate [Member] | Total Commercial [Member] | Doubtful [Member]
Financing Receivable, Recorded Investment [Line Items]
Total loans	57	17,702
Total Commercial And Industrial [Member] | Commercial Real Estate - Owner Occupied [Member] | Total Commercial [Member]
Financing Receivable, Recorded Investment [Line Items]
Total loans	2,142,439	1,906,821
Total Commercial And Industrial [Member] | Commercial Real Estate - Owner Occupied [Member] | Total Commercial [Member] | Pass [Member]
Financing Receivable, Recorded Investment [Line Items]
Total loans	1,896,366	1,719,114
Total Commercial And Industrial [Member] | Commercial Real Estate - Owner Occupied [Member] | Total Commercial [Member] | Pass-Watch [Member]
Financing Receivable, Recorded Investment [Line Items]
Total loans	82,913	47,676
Total Commercial And Industrial [Member] | Commercial Real Estate - Owner Occupied [Member] | Total Commercial [Member] | Special Mention [Member]
Financing Receivable, Recorded Investment [Line Items]
Total loans	27,456	40,299
Total Commercial And Industrial [Member] | Commercial Real Estate - Owner Occupied [Member] | Total Commercial [Member] | Substandard [Member]
Financing Receivable, Recorded Investment [Line Items]
Total loans	135,704	99,732
Performing [Member] | Residential Mortgages [Member]
Financing Receivable, Recorded Investment [Line Items]
Total loans	2,647,784	2,123,048
Performing [Member] | Consumer [Member]
Financing Receivable, Recorded Investment [Line Items]
Total loans	2,099,637	2,046,757
Performing [Member] | Residential Mortgage and Consumer [Member]
Financing Receivable, Recorded Investment [Line Items]
Total loans	4,747,421	4,169,805
Nonperforming [Member] | Residential Mortgages [Member]
Financing Receivable, Recorded Investment [Line Items]
Total loans	42,688	23,665
Nonperforming [Member] | Consumer [Member]
Financing Receivable, Recorded Investment [Line Items]
Total loans	15,658	13,174
Nonperforming [Member] | Residential Mortgage and Consumer [Member]
Financing Receivable, Recorded Investment [Line Items]
Total loans	$ 58,346	$ 36,839