Revenue from Contracts with Customers (Schedule of Disaggregation of Revenue) (Details) - USD ($) $ in Thousands	3 Months Ended		6 Months Ended
	Jun. 30, 2018	Jun. 30, 2017	Jun. 30, 2018	Jun. 30, 2017
Disaggregation of Revenue [Line Items]
Non-interest income	$ 124,850	$ 115,380	$ 244,540	$ 224,993
Revenue from Contracts with Customers In Scope of ASC 606 [Member]
Disaggregation of Revenue [Line Items]
Non-interest income	114,967	105,572	226,543	206,525
Revenue from Contracts with Customers In Scope of ASC 606 [Member] | Bank Card Transaction Fees [Member]
Disaggregation of Revenue [Line Items]
Non-interest income	43,215	37,295	84,668	73,046
Revenue from Contracts with Customers In Scope of ASC 606 [Member] | Trust Fees [Member]
Disaggregation of Revenue [Line Items]
Non-interest income	37,036	33,120	73,098	65,134
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	23,893	22,861	46,875	44,803
Revenue from Contracts with Customers In Scope of ASC 606 [Member] | Consumer Brokerage Services [Member]
Disaggregation of Revenue [Line Items]
Non-interest income	3,971	3,726	7,739	7,375
Revenue from Contracts with Customers In Scope of ASC 606 [Member] | Other Non-Interest Income [Member]
Disaggregation of Revenue [Line Items]
Non-interest income	6,852	8,570	14,163	16,167
Revenue Not In Scope of ASC 606 [Member]
Disaggregation of Revenue [Line Items]
Non-interest income	$ 9,883	$ 9,808	$ 17,997	$ 18,468