Basis of Presentation and Accounting Policies (Schedule of Adoption) (Details) - USD ($) $ in Thousands	Sep. 30, 2020	Jun. 30, 2020	Jan. 01, 2020	Dec. 31, 2019	Sep. 30, 2019	Jun. 30, 2019	Dec. 31, 2018
New Accounting Pronouncements or Change in Accounting Principle [Line Items]
Total allowance for loan losses	$ 603,800	$ 588,648	$ 281,402	$ 281,402	$ 265,013	$ 257,376	$ 250,555
Reserve for unfunded commitments			1,375
Allowance for credit losses	664,600		282,777
Loans, net			36,881,048
Retained earnings	1,084,736		1,068,327	1,068,327
Total commercial and industrial
New Accounting Pronouncements or Change in Accounting Principle [Line Items]
Total allowance for loan losses	260,600	229,915	145,782		142,011	138,004	133,123
Total commercial real estate
New Accounting Pronouncements or Change in Accounting Principle [Line Items]
Total allowance for loan losses	143,805	171,526	67,430		61,958	63,463	68,796
Retail
New Accounting Pronouncements or Change in Accounting Principle [Line Items]
Total allowance for loan losses	$ 199,395	$ 187,207	68,190		$ 61,044	$ 55,909	$ 48,636
Impact of ASC 326 Adoption
New Accounting Pronouncements or Change in Accounting Principle [Line Items]
Total allowance for loan losses			82,994	82,994
Reserve for unfunded commitments			27,440
Allowance for credit losses			110,434
Loans, net			(20,767)
Retained earnings			(35,721)
Impact of ASC 326 Adoption | Total commercial and industrial
New Accounting Pronouncements or Change in Accounting Principle [Line Items]
Total allowance for loan losses			(2,310)	(2,310)
Impact of ASC 326 Adoption | Total commercial real estate
New Accounting Pronouncements or Change in Accounting Principle [Line Items]
Total allowance for loan losses			(651)	(651)
Impact of ASC 326 Adoption | Retail
New Accounting Pronouncements or Change in Accounting Principle [Line Items]
Total allowance for loan losses			85,955	$ 85,955
As Reported under ASC 326
New Accounting Pronouncements or Change in Accounting Principle [Line Items]
Total allowance for loan losses			364,396
Reserve for unfunded commitments			28,815
Allowance for credit losses			393,211
Loans, net			36,860,281
Retained earnings			1,032,606
As Reported under ASC 326 | Total commercial and industrial
New Accounting Pronouncements or Change in Accounting Principle [Line Items]
Total allowance for loan losses			143,472
As Reported under ASC 326 | Total commercial real estate
New Accounting Pronouncements or Change in Accounting Principle [Line Items]
Total allowance for loan losses			66,779
As Reported under ASC 326 | Retail
New Accounting Pronouncements or Change in Accounting Principle [Line Items]
Total allowance for loan losses			$ 154,145