Revenue from Contracts with Customers (Schedule of Disaggregation of Revenue) (Details) - USD ($) $ in Thousands	3 Months Ended		9 Months Ended
	Sep. 30, 2018	Sep. 30, 2017	Sep. 30, 2018	Sep. 30, 2017
Disaggregation of Revenue [Line Items]
Non-interest income	$ 123,714	$ 116,887	$ 368,254	$ 341,880
Revenue from Contracts with Customers In Scope of ASC 606 [Member]
Disaggregation of Revenue [Line Items]
Non-interest income	114,443	107,580	340,986	314,104
Revenue from Contracts with Customers In Scope of ASC 606 [Member] | Bank Card Transaction Fees [Member]
Disaggregation of Revenue [Line Items]
Non-interest income	42,427	39,166	127,095	112,212
Revenue from Contracts with Customers In Scope of ASC 606 [Member] | Trust Fees [Member]
Disaggregation of Revenue [Line Items]
Non-interest income	37,400	34,620	110,498	99,754
Revenue from Contracts with Customers In Scope of ASC 606 [Member] | Deposit Account Charges and Other Fees [Member]
Disaggregation of Revenue [Line Items]
Non-interest income	23,755	22,659	70,630	67,462
Revenue from Contracts with Customers In Scope of ASC 606 [Member] | Consumer Brokerage Services [Member]
Disaggregation of Revenue [Line Items]
Non-interest income	3,884	3,679	11,623	11,054
Revenue from Contracts with Customers In Scope of ASC 606 [Member] | Other Non-Interest Income [Member]
Disaggregation of Revenue [Line Items]
Non-interest income	6,977	7,456	21,140	23,622
Revenue Not In Scope of ASC 606 [Member]
Disaggregation of Revenue [Line Items]
Non-interest income	$ 9,271	$ 9,307	$ 27,268	$ 27,776