Contract Balances and Performance Obligations - Contract Balances (Details) - USD ($) $ in Thousands	6 Months Ended
	Mar. 31, 2021	Sep. 30, 2020
Contract With Customer, Liability [Roll Forward]
Deferred revenues at September 30, 2020 *	$ 122,141
Revenue recognized that was included in the deferred revenues balance at the beginning of the period	(75,600)
Increases due to billings, excluding amounts recognized as revenue during the period	78,945
Reclassified as liabilities related to assets held for sale	(16,508)
Deferred revenues at March 31, 2021 *	108,978
Deferred revenue and other liabilities, current portion	100,400	$ 115,200
Deferred revenue and other liabilities, noncurrent	$ 8,600	$ 6,900