Restructuring and Other Costs, Net - Schedule of Accrual Activity Relating to Restructuring Charges (Details) - USD ($) $ in Thousands	12 Months Ended
	Sep. 30, 2020	Sep. 30, 2019	Sep. 30, 2018
Restructuring Cost And Reserve [Line Items]
Balance at October 1, 2017	$ 4,391	$ 3,052	$ 222
Restructuring and other costs, net	18,237	24,404	12,863
Non-cash adjustment	(1,031)
Cash payments	(17,121)	(23,065)	(10,033)
Foreign exchange impact on ending balance	(39)
Balance at September 30, 2018	4,437	4,391	3,052
Personnel
Restructuring Cost And Reserve [Line Items]
Balance at October 1, 2017	489	2,269	108
Restructuring and other costs, net	3,694	130	4,130
Cash payments	(3,420)	(1,910)	(1,969)
Foreign exchange impact on ending balance	1
Balance at September 30, 2018	764	489	2,269
Facilities
Restructuring Cost And Reserve [Line Items]
Balance at October 1, 2017	26	6	114
Restructuring and other costs, net	2,816	1,704	20
Non-cash adjustment	(1,031)
Cash payments	(26)	(1,684)	(128)
Foreign exchange impact on ending balance	(40)
Balance at September 30, 2018	1,745	26	6
Spin-Off
Restructuring Cost And Reserve [Line Items]
Balance at October 1, 2017	3,876	777
Restructuring and other costs, net	11,727	22,570	8,713
Cash payments	(13,675)	(19,471)	(7,936)
Balance at September 30, 2018	$ 1,928	$ 3,876	$ 777