Revenue - Contract Balances (Details) - USD ($) $ in Thousands	12 Months Ended
	Sep. 30, 2020	Sep. 30, 2019
Change In Contract With Customer, Assets [Roll Forward]
Contract assets - Beginning balance	$ 10,349	$ 10,140
Additional revenue recognized over-time	67,043	62,499
Less amounts billed to the customers	(65,395)	(62,290)
Contract assets - Ending balance	11,997	10,349
Change In Contract With Customer, Liability [Roll Forward]
Contract liabilities (included within Accrued liabilities) - Beginning balance	(382)	0
Payments received in advance of performance obligations	(865)	(2,000)
Performance obligations satisfied	611	1,618
Contract liabilities (included within Accrued liabilities) - Ending balance	$ (636)	$ (382)