Loans and Allowance for Loan Losses (Credit Quality Indicators by Segments and Portfolio Class) (Details) - USD ($) $ in Thousands	Mar. 31, 2018	Dec. 31, 2017
Total Commercial [Member]
Financing Receivable, Recorded Investment [Line Items]
Total loans	$ 14,330,505	$ 14,198,396
Total Commercial [Member] | Pass [Member]
Financing Receivable, Recorded Investment [Line Items]
Total loans	12,807,913	12,601,853
Total Commercial [Member] | Pass-Watch [Member]
Financing Receivable, Recorded Investment [Line Items]
Total loans	438,813	520,230
Total Commercial [Member] | Special Mention [Member]
Financing Receivable, Recorded Investment [Line Items]
Total loans	151,599	126,137
Total Commercial [Member] | Substandard [Member]
Financing Receivable, Recorded Investment [Line Items]
Total loans	932,162	950,111
Total Commercial [Member] | Doubtful [Member]
Financing Receivable, Recorded Investment [Line Items]
Total loans	18	65
Residential Mortgages [Member]
Financing Receivable, Recorded Investment [Line Items]
Total loans	2,732,821	2,690,472
Consumer [Member]
Financing Receivable, Recorded Investment [Line Items]
Total loans	2,029,178	2,115,295
Residential Mortgage and Consumer [Member]
Financing Receivable, Recorded Investment [Line Items]
Total loans	4,761,999	4,805,767
Commercial Real Estate - Income Producing [Member] | Total Commercial [Member]
Financing Receivable, Recorded Investment [Line Items]
Total loans	2,394,862	2,384,599
Commercial Real Estate - Income Producing [Member] | Total Commercial [Member] | Pass [Member]
Financing Receivable, Recorded Investment [Line Items]
Total loans	2,268,358	2,223,245
Commercial Real Estate - Income Producing [Member] | Total Commercial [Member] | Pass-Watch [Member]
Financing Receivable, Recorded Investment [Line Items]
Total loans	58,092	83,444
Commercial Real Estate - Income Producing [Member] | Total Commercial [Member] | Special Mention [Member]
Financing Receivable, Recorded Investment [Line Items]
Total loans	9,344	13,244
Commercial Real Estate - Income Producing [Member] | Total Commercial [Member] | Substandard [Member]
Financing Receivable, Recorded Investment [Line Items]
Total loans	59,068	64,658
Commercial Real Estate - Income Producing [Member] | Total Commercial [Member] | Doubtful [Member]
Financing Receivable, Recorded Investment [Line Items]
Total loans		8
Construction and Land Development [Member] | Total Commercial [Member]
Financing Receivable, Recorded Investment [Line Items]
Total loans	1,413,878	1,373,421
Construction and Land Development [Member] | Total Commercial [Member] | Pass [Member]
Financing Receivable, Recorded Investment [Line Items]
Total loans	1,334,456	1,291,638
Construction and Land Development [Member] | Total Commercial [Member] | Pass-Watch [Member]
Financing Receivable, Recorded Investment [Line Items]
Total loans	59,208	60,804
Construction and Land Development [Member] | Total Commercial [Member] | Special Mention [Member]
Financing Receivable, Recorded Investment [Line Items]
Total loans	6,279	4,788
Construction and Land Development [Member] | Total Commercial [Member] | Substandard [Member]
Financing Receivable, Recorded Investment [Line Items]
Total loans	13,935	16,191
Total Commercial And Industrial [Member] | Total Commercial [Member]
Financing Receivable, Recorded Investment [Line Items]
Total loans	10,521,765	10,440,376
Total Commercial And Industrial [Member] | Total Commercial [Member] | Pass [Member]
Financing Receivable, Recorded Investment [Line Items]
Total loans	9,205,099	9,086,970
Total Commercial And Industrial [Member] | Total Commercial [Member] | Pass-Watch [Member]
Financing Receivable, Recorded Investment [Line Items]
Total loans	321,513	375,982
Total Commercial And Industrial [Member] | Total Commercial [Member] | Special Mention [Member]
Financing Receivable, Recorded Investment [Line Items]
Total loans	135,976	108,105
Total Commercial And Industrial [Member] | Total Commercial [Member] | Substandard [Member]
Financing Receivable, Recorded Investment [Line Items]
Total loans	859,159	869,262
Total Commercial And Industrial [Member] | Total Commercial [Member] | Doubtful [Member]
Financing Receivable, Recorded Investment [Line Items]
Total loans	18	57
Total Commercial And Industrial [Member] | Commercial Non-Real Estate [Member] | Total Commercial [Member]
Financing Receivable, Recorded Investment [Line Items]
Total loans	8,336,222	8,297,937
Total Commercial And Industrial [Member] | Commercial Non-Real Estate [Member] | Total Commercial [Member] | Pass [Member]
Financing Receivable, Recorded Investment [Line Items]
Total loans	7,250,715	7,190,604
Total Commercial And Industrial [Member] | Commercial Non-Real Estate [Member] | Total Commercial [Member] | Pass-Watch [Member]
Financing Receivable, Recorded Investment [Line Items]
Total loans	269,657	293,069
Total Commercial And Industrial [Member] | Commercial Non-Real Estate [Member] | Total Commercial [Member] | Special Mention [Member]
Financing Receivable, Recorded Investment [Line Items]
Total loans	100,005	80,649
Total Commercial And Industrial [Member] | Commercial Non-Real Estate [Member] | Total Commercial [Member] | Substandard [Member]
Financing Receivable, Recorded Investment [Line Items]
Total loans	715,827	733,558
Total Commercial And Industrial [Member] | Commercial Non-Real Estate [Member] | Total Commercial [Member] | Doubtful [Member]
Financing Receivable, Recorded Investment [Line Items]
Total loans	18	57
Total Commercial And Industrial [Member] | Commercial Real Estate - Owner Occupied [Member] | Total Commercial [Member]
Financing Receivable, Recorded Investment [Line Items]
Total loans	2,185,543	2,142,439
Total Commercial And Industrial [Member] | Commercial Real Estate - Owner Occupied [Member] | Total Commercial [Member] | Pass [Member]
Financing Receivable, Recorded Investment [Line Items]
Total loans	1,954,384	1,896,366
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	51,856	82,913
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	35,971	27,456
Total Commercial And Industrial [Member] | Commercial Real Estate - Owner Occupied [Member] | Total Commercial [Member] | Substandard [Member]
Financing Receivable, Recorded Investment [Line Items]
Total loans	143,332	135,704
Performing [Member] | Residential Mortgages [Member]
Financing Receivable, Recorded Investment [Line Items]
Total loans	2,696,582	2,647,784
Performing [Member] | Consumer [Member]
Financing Receivable, Recorded Investment [Line Items]
Total loans	2,014,442	2,099,637
Performing [Member] | Residential Mortgage and Consumer [Member]
Financing Receivable, Recorded Investment [Line Items]
Total loans	4,711,024	4,747,421
Nonperforming [Member] | Residential Mortgages [Member]
Financing Receivable, Recorded Investment [Line Items]
Total loans	36,239	42,688
Nonperforming [Member] | Consumer [Member]
Financing Receivable, Recorded Investment [Line Items]
Total loans	14,736	15,658
Nonperforming [Member] | Residential Mortgage and Consumer [Member]
Financing Receivable, Recorded Investment [Line Items]
Total loans	$ 50,975	$ 58,346