Discontinued Operations, Goodwill, and Intangible Assets - Intangible Assets (Details) - USD ($) $ in Thousands	12 Months Ended
	Sep. 30, 2021	Sep. 30, 2020
Identifiable intangible assets with finite useful lives
Intangible Assets, Net	$ 54,867	$ 76,917
Backlog and customer relationships
Identifiable intangible assets with finite useful lives
Gross Amount	663,400	662,800
Accumulated Amortization	(608,500)	(585,900)
Intangible Assets, Net	$ 54,900	$ 76,900
Backlog and customer relationships | Minimum
Identifiable intangible assets with finite useful lives
Amortization Period	1 year
Backlog and customer relationships | Maximum
Identifiable intangible assets with finite useful lives
Amortization Period	11 years