Goodwill And Intangible Assets (Narrative) (Details) - USD ($) $ in Thousands	3 Months Ended		9 Months Ended
	Sep. 30, 2018	Sep. 30, 2017	Sep. 30, 2018	Sep. 30, 2017	Mar. 19, 2018	Dec. 31, 2017
Schedule of Goodwill and Intangible Assets [Line Items]
Goodwill	$ 1,025,714		$ 1,025,714			$ 968,834
Amortization of intangible assets	3,000	$ 2,900	$ 8,741	$ 9,092
Customer Relationships [Member]
Schedule of Goodwill and Intangible Assets [Line Items]
Weighted-average remaining lives of intangible assets			10 years 8 months 12 days
Trade Name [Member]
Schedule of Goodwill and Intangible Assets [Line Items]
Weighted-average remaining lives of intangible assets			9 years 8 months 12 days
Non-Compete Agreements [Member]
Schedule of Goodwill and Intangible Assets [Line Items]
Weighted-average remaining lives of intangible assets			8 years 9 months 18 days
BBI Intangibles [Member]
Schedule of Goodwill and Intangible Assets [Line Items]
Weighted-average remaining lives of intangible assets			5 years
Ziegler [Member]
Schedule of Goodwill and Intangible Assets [Line Items]
Goodwill	19,000		$ 19,000
Ziegler [Member] | Customer Relationships and Non-Compete Agreements [Member]
Schedule of Goodwill and Intangible Assets [Line Items]
Identifiable intangible assets					$ 9,500
Business Bancshares, Inc. [Member]
Schedule of Goodwill and Intangible Assets [Line Items]
Goodwill and intangible assets	$ 46,400		$ 46,400