Supplementary Balance Sheet Information - Allowance for Doubtful Accounts Activity (Details) - Allowance for Doubtful Accounts - USD ($) $ in Thousands	12 Months Ended
	Sep. 30, 2020	Sep. 30, 2019	Sep. 30, 2018
Movement in Valuation Allowances and Reserves [Roll Forward]
Valuation Allowances and Reserves, Balance, Beginning Balance	$ 3,644	$ 1,113	$ 1,381
Provisions	4,587	3,405	708
Reversals of Bad Debt Expense	(1,018)	(693)	(724)
Write-offs and Adjustments	3	(181)	(252)
Valuation Allowances and Reserves, Balance, Ending Balance	$ 7,216	$ 3,644	$ 1,113