Goodwill and Other Intangible Assets (Narrative) (Details) - USD ($) $ in Thousands	12 Months Ended
	Dec. 31, 2017	Dec. 31, 2016	Dec. 31, 2015
Finite-Lived Intangible Assets [Line Items]
Goodwill	$ 745,523	$ 621,193
Goodwill impairment charges	$ 0	$ 0	$ 0
Core Deposit Intangibles [Member]
Finite-Lived Intangible Assets [Line Items]
Weighted-average remaining life	9 years
Other Identifiable Intangibles [Member]
Finite-Lived Intangible Assets [Line Items]
Weighted-average remaining life	6 years
FNBC Transaction [Member]
Finite-Lived Intangible Assets [Line Items]
Goodwill	$ 124,330