Revenue from Contracts with Customers (Schedule of Disaggregation of Revenue) (Details) - USD ($) $ in Thousands	3 Months Ended
	Mar. 31, 2018	Mar. 31, 2017
Disaggregation of Revenue [Line Items]
Non-interest income	$ 119,690	$ 109,613
Revenue from Contracts with Customers In Scope of ASC 606 [Member]
Disaggregation of Revenue [Line Items]
Non-interest income	111,576	100,953
Revenue from Contracts with Customers In Scope of ASC 606 [Member] | Bank Card Transaction Fees [Member]
Disaggregation of Revenue [Line Items]
Non-interest income	41,453	35,751
Revenue from Contracts with Customers In Scope of ASC 606 [Member] | Trust Fees [Member]
Disaggregation of Revenue [Line Items]
Non-interest income	36,062	32,014
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	22,982	21,942
Revenue from Contracts with Customers In Scope of ASC 606 [Member] | Consumer Brokerage Services [Member]
Disaggregation of Revenue [Line Items]
Non-interest income	3,768	3,649
Revenue from Contracts with Customers In Scope of ASC 606 [Member] | Other Non-Interest Income [Member]
Disaggregation of Revenue [Line Items]
Non-interest income	7,311	7,597
Revenue Not In Scope of ASC 606 [Member]
Disaggregation of Revenue [Line Items]
Non-interest income	$ 8,114	$ 8,660