Acquisitions Of Businesses (Details) $ in Thousands	Mar. 01, 2017 USD ($) Company	Jan. 04, 2017 Company	Apr. 15, 2016 USD ($) Company	Apr. 01, 2016 Company	Sep. 30, 2017 USD ($)	Dec. 31, 2016 USD ($)
Business Acquisition [Line Items]
Goodwill					$ 1,010,399	$ 979,628
Number of businesses acquired | Company	1	1	1	1
Q1 2017 Acquisitions [Member]
Business Acquisition [Line Items]
Purchase price	$ 84,800
Working capital acquired	9,600
Other net assets	300
Goodwill	28,700
Identifiable intangible assets	$ 46,200
Ardent [Member]
Business Acquisition [Line Items]
Business acquisition, percentage of voting interests acquired			100.00%
Purchase price			$ 201,400
Working capital acquired			34,100
Other net assets			3,900
Goodwill			121,900
Identifiable intangible assets			41,500
Acquired goodwill, tax deductible amount			$ 99,700
Intangible amortization period			13 years 6 months