Supplementary Balance Sheet Information - Valuation Allowance for Deferred Tax Assets Activity (Details) - Valuation Allowance of Deferred Tax Assets - 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	$ 16,093	$ 18,581	$ 92,297
Charged to Provisions	(1,526)	(3,475)	(72,842)
Charged to Other Accounts	(968)	987	(874)
Valuation Allowances and Reserves, Balance, Ending Balance	$ 13,599	$ 16,093	$ 18,581