Restructuring and Other Costs, Net - Schedule of Accrual Activity Relating to Restructuring Reserves (Details) - USD ($) $ in Thousands	3 Months Ended		6 Months Ended
	Mar. 31, 2021	Mar. 31, 2020	Mar. 31, 2021	Mar. 31, 2020
Restructuring Cost And Reserve [Line Items]
Balance at September 30, 2020			$ 2,702
Restructuring and other costs, net	$ 537	$ 2,870	1,017	$ 10,424
Non-cash adjustments			2,749
Cash (payments) receipts			(3,090)
Foreign exchange impact on ending balance			(24)
Balance at March 31, 2021	3,354		3,354
Personnel
Restructuring Cost And Reserve [Line Items]
Balance at September 30, 2020			764
Restructuring and other costs, net	45	321	381	681
Cash (payments) receipts			(719)
Foreign exchange impact on ending balance			6
Balance at March 31, 2021	432		432
Facilities
Restructuring Cost And Reserve [Line Items]
Balance at September 30, 2020			10
Restructuring and other costs, net	447		565
Non-cash adjustments			2,749
Cash (payments) receipts			(372)
Foreign exchange impact on ending balance			(30)
Balance at March 31, 2021	2,922		2,922
Restructuring Subtotal
Restructuring Cost And Reserve [Line Items]
Balance at September 30, 2020			774
Restructuring and other costs, net	492	321	946	681
Non-cash adjustments			2,749
Cash (payments) receipts			(1,091)
Foreign exchange impact on ending balance			(24)
Balance at March 31, 2021	3,354		3,354
Other
Restructuring Cost And Reserve [Line Items]
Balance at September 30, 2020			1,928
Restructuring and other costs, net	$ 45	$ 2,549	71	$ 9,743
Cash (payments) receipts			$ (1,999)