Revenue - Contract Balances (Details) - USD ($)	12 Months Ended
	Sep. 30, 2021	Sep. 30, 2020
Change In Contract With Customer, Assets [Roll Forward]
Contract assets - Beginning balance	$ 11,997,000	$ 10,349,000
Additional revenue recognized over-time	64,384,000	67,043,000
Less amounts billed to the customers	(63,507,000)	(65,395,000)
Contract assets - Ending balance	12,874,000	11,997,000
Change In Contract With Customer, Liability [Roll Forward]
Contract liabilities (included within Accrued liabilities) - Beginning balance	(636,000)	(382,000)
Payments received in advance of performance obligations	(829,000)	(865,000)
Performance obligations satisfied	1,229,000	611,000
Contract liabilities (included within Accrued liabilities) - Ending balance	(236,000)	(636,000)
Impairment loss on contract assets	$ 0	$ 0