Intangible Assets, Goodwill and Acquisitions - Schedule of Intangible Assets (Details) - USD ($) $ in Thousands	6 Months Ended
	Mar. 31, 2019	Sep. 30, 2018
Finite Lived Intangible Assets [Line Items]
Gross Carrying Amount	$ 642,934	$ 855,930
Accumulated Amortization	(368,313)	(565,475)
Customer Relationships
Finite Lived Intangible Assets [Line Items]
Gross Carrying Amount	635,394	622,710
Accumulated Amortization	$ (366,417)	(337,800)
Customer Relationships | Minimum
Finite Lived Intangible Assets [Line Items]
Useful Life	6 years
Customer Relationships | Maximum
Finite Lived Intangible Assets [Line Items]
Useful Life	21 years
Trademarks
Finite Lived Intangible Assets [Line Items]
Gross Carrying Amount	$ 4,800	230,900
Accumulated Amortization	$ (1,504)	(227,520)
Trademarks | Minimum
Finite Lived Intangible Assets [Line Items]
Useful Life	4 years
Trademarks | Maximum
Finite Lived Intangible Assets [Line Items]
Useful Life	12 years
Noncompete Agreements
Finite Lived Intangible Assets [Line Items]
Gross Carrying Amount	$ 2,740	2,320
Accumulated Amortization	$ (392)	$ (155)
Noncompete Agreements | Minimum
Finite Lived Intangible Assets [Line Items]
Useful Life	5 years