Contract Balances and Performance Obligation - Contract Balances (Details) - USD ($) $ in Thousands	6 Months Ended
	Mar. 31, 2020	Sep. 30, 2019
Contract With Customer, Liability [Roll Forward]
Deferred revenues at September 30, 2019	$ 116,320
Revenue recognized that was included in the deferred revenues balance at the beginning of the period	(75,148)
Increases due to billings, excluding amounts recognized as revenue during the period	80,382
Deferred revenues at March 31, 2020	121,554
Deferred revenue and other liabilities, current portion	114,400	$ 111,000
Deferred revenue and other liabilities, noncurrent	$ 7,200	$ 5,300