Supplementary Balance Sheet Information - Allowance for Doubtful Accounts Activity (Details) - Allowance for Doubtful Accounts - USD ($) $ in Thousands	12 Months Ended
	Sep. 30, 2019	Sep. 30, 2018	Sep. 30, 2017
Movement in Valuation Allowances and Reserves [Roll Forward]
Valuation Allowances and Reserves, Balance, Beginning Balance	$ 1,113	$ 1,381	$ 1,543
Provisions	3,405	708
Reversals of Bad Debt Expense	(693)	(724)	(131)
Write-offs and Adjustments	(181)	(252)	(31)
Valuation Allowances and Reserves, Balance, Ending Balance	$ 3,644	$ 1,113	$ 1,381