Loans and Allowance for Loan Losses (Credit Quality Indicators by Segments and Portfolio Class) (Details) - USD ($) $ in Thousands	Mar. 31, 2019	Dec. 31, 2018
Total Commercial [Member]
Financing Receivable Recorded Investment [Line Items]
Total loans	$ 15,075,215	$ 14,968,463
Total Commercial [Member] | Total Commercial And Industrial [Member]
Financing Receivable Recorded Investment [Line Items]
Total loans	11,171,754	11,078,349
Total Commercial [Member] | Pass [Member]
Financing Receivable Recorded Investment [Line Items]
Total loans	14,141,690	13,902,485
Total Commercial [Member] | Pass [Member] | Total Commercial And Industrial [Member]
Financing Receivable Recorded Investment [Line Items]
Total loans	10,371,654	10,149,799
Total Commercial [Member] | Pass-Watch [Member]
Financing Receivable Recorded Investment [Line Items]
Total loans	349,301	440,415
Total Commercial [Member] | Pass-Watch [Member] | Total Commercial And Industrial [Member]
Financing Receivable Recorded Investment [Line Items]
Total loans	257,840	344,781
Total Commercial [Member] | Special Mention [Member]
Financing Receivable Recorded Investment [Line Items]
Total loans	90,639	105,227
Total Commercial [Member] | Special Mention [Member] | Total Commercial And Industrial [Member]
Financing Receivable Recorded Investment [Line Items]
Total loans	78,989	98,901
Total Commercial [Member] | Substandard [Member]
Financing Receivable Recorded Investment [Line Items]
Total loans	493,585	520,336
Total Commercial [Member] | Substandard [Member] | Total Commercial And Industrial [Member]
Financing Receivable Recorded Investment [Line Items]
Total loans	463,271	484,868
Residential Mortgages [Member]
Financing Receivable Recorded Investment [Line Items]
Total loans	2,933,251	2,910,081
Residential Mortgages [Member] | Performing [Member]
Financing Receivable Recorded Investment [Line Items]
Total loans	2,893,635	2,873,669
Residential Mortgages [Member] | Nonperforming [Member]
Financing Receivable Recorded Investment [Line Items]
Total loans	39,616	36,412
Consumer [Member]
Financing Receivable Recorded Investment [Line Items]
Total loans	2,104,372	2,147,867
Consumer [Member] | Performing [Member]
Financing Receivable Recorded Investment [Line Items]
Total loans	2,085,456	2,130,395
Consumer [Member] | Nonperforming [Member]
Financing Receivable Recorded Investment [Line Items]
Total loans	18,916	17,472
Residential Mortgage and Consumer [Member]
Financing Receivable Recorded Investment [Line Items]
Total loans	5,037,623	5,057,948
Residential Mortgage and Consumer [Member] | Performing [Member]
Financing Receivable Recorded Investment [Line Items]
Total loans	4,979,091	5,004,064
Residential Mortgage and Consumer [Member] | Nonperforming [Member]
Financing Receivable Recorded Investment [Line Items]
Total loans	58,532	53,884
Commercial Non-Real Estate [Member] | Total Commercial [Member] | Total Commercial And Industrial [Member]
Financing Receivable Recorded Investment [Line Items]
Total loans	8,656,326	8,620,601
Commercial Non-Real Estate [Member] | Total Commercial [Member] | Pass [Member] | Total Commercial And Industrial [Member]
Financing Receivable Recorded Investment [Line Items]
Total loans	8,028,706	7,875,588
Commercial Non-Real Estate [Member] | Total Commercial [Member] | Pass-Watch [Member] | Total Commercial And Industrial [Member]
Financing Receivable Recorded Investment [Line Items]
Total loans	166,406	260,510
Commercial Non-Real Estate [Member] | Total Commercial [Member] | Special Mention [Member] | Total Commercial And Industrial [Member]
Financing Receivable Recorded Investment [Line Items]
Total loans	62,830	75,752
Commercial Non-Real Estate [Member] | Total Commercial [Member] | Substandard [Member] | Total Commercial And Industrial [Member]
Financing Receivable Recorded Investment [Line Items]
Total loans	398,384	408,751
Commercial Real Estate - Owner Occupied [Member] | Total Commercial [Member] | Total Commercial And Industrial [Member]
Financing Receivable Recorded Investment [Line Items]
Total loans	2,515,428	2,457,748
Commercial Real Estate - Owner Occupied [Member] | Total Commercial [Member] | Pass [Member] | Total Commercial And Industrial [Member]
Financing Receivable Recorded Investment [Line Items]
Total loans	2,342,948	2,274,211
Commercial Real Estate - Owner Occupied [Member] | Total Commercial [Member] | Pass-Watch [Member] | Total Commercial And Industrial [Member]
Financing Receivable Recorded Investment [Line Items]
Total loans	91,434	84,271
Commercial Real Estate - Owner Occupied [Member] | Total Commercial [Member] | Special Mention [Member] | Total Commercial And Industrial [Member]
Financing Receivable Recorded Investment [Line Items]
Total loans	16,159	23,149
Commercial Real Estate - Owner Occupied [Member] | Total Commercial [Member] | Substandard [Member] | Total Commercial And Industrial [Member]
Financing Receivable Recorded Investment [Line Items]
Total loans	64,887	76,117
Commercial Real Estate - Income Producing [Member] | Total Commercial [Member]
Financing Receivable Recorded Investment [Line Items]
Total loans	2,563,394	2,341,779
Commercial Real Estate - Income Producing [Member] | Total Commercial [Member] | Pass [Member]
Financing Receivable Recorded Investment [Line Items]
Total loans	2,450,517	2,265,087
Commercial Real Estate - Income Producing [Member] | Total Commercial [Member] | Pass-Watch [Member]
Financing Receivable Recorded Investment [Line Items]
Total loans	81,718	46,535
Commercial Real Estate - Income Producing [Member] | Total Commercial [Member] | Special Mention [Member]
Financing Receivable Recorded Investment [Line Items]
Total loans	10,760	5,510
Commercial Real Estate - Income Producing [Member] | Total Commercial [Member] | Substandard [Member]
Financing Receivable Recorded Investment [Line Items]
Total loans	20,399	24,647
Construction and Land Development [Member] | Total Commercial [Member]
Financing Receivable Recorded Investment [Line Items]
Total loans	1,340,067	1,548,335
Construction and Land Development [Member] | Total Commercial [Member] | Pass [Member]
Financing Receivable Recorded Investment [Line Items]
Total loans	1,319,519	1,487,599
Construction and Land Development [Member] | Total Commercial [Member] | Pass-Watch [Member]
Financing Receivable Recorded Investment [Line Items]
Total loans	9,743	49,099
Construction and Land Development [Member] | Total Commercial [Member] | Special Mention [Member]
Financing Receivable Recorded Investment [Line Items]
Total loans	890	816
Construction and Land Development [Member] | Total Commercial [Member] | Substandard [Member]
Financing Receivable Recorded Investment [Line Items]
Total loans	$ 9,915	$ 10,821