Goodwill And Intangible Assets - Components of Goodwill and Intangible Assets (Details) - USD ($) $ in Thousands	Dec. 31, 2017	Sep. 30, 2017	Dec. 31, 2016
Goodwill and Intangible Assets Disclosure [Abstract]
Goodwill (not subject to amortization)	$ 2,002,010	$ 2,002,010	$ 1,979,146
Intangible assets:
Customer relationships and noncompete agreements	496,905	497,385	520,480
Accumulated amortization	(199,416)	(190,289)	(201,236)
Intangible assets, net (definite-lived)	297,489	307,096	319,244
Trademarks and tradenames (indefinite-lived)	82,944	82,944	82,944
Total intangible assets, net	$ 380,433	$ 390,040	$ 402,188