Supplementary Balance Sheet Information - Allowance for Expected Credit Losses Activity (Details) - USD ($) $ in Thousands	12 Months Ended
	Sep. 30, 2023	Sep. 30, 2022	Sep. 30, 2021
Accounts Receivable, Allowance for Credit Loss [Roll Forward]
Balance at beginning of period	$ 5,162	$ 4,318	$ 7,146
Provisions	8,849	3,536	3,445
Payments received	(5,884)	(2,278)	(5,481)
Write-offs and adjustments	(70)	(414)	(792)
Balance at end of period	$ 8,057	$ 5,162	$ 4,318