Goodwill and Other Intangible Assets (Carrying Value of Intangible Assets Subject to Amortization) (Details) - USD ($) $ in Thousands	Dec. 31, 2017	Dec. 31, 2016
Finite-Lived Intangible Assets [Line Items]
Purchase Value	$ 248,355	$ 223,055
Accumulated Amortization	157,715	135,298
Carrying Value	90,640	87,757
Core Deposit Intangibles [Member]
Finite-Lived Intangible Assets [Line Items]
Purchase Value	215,955	190,655
Accumulated Amortization	132,878	113,436
Carrying Value	83,077	77,219
Credit Card and Trust Relationships [Member]
Finite-Lived Intangible Assets [Line Items]
Purchase Value	22,400	22,400
Accumulated Amortization	16,882	14,907
Carrying Value	5,518	7,493
Merchant Processing Relationships [Member]
Finite-Lived Intangible Assets [Line Items]
Purchase Value	10,000	10,000
Accumulated Amortization	7,955	6,955
Carrying Value	$ 2,045	$ 3,045