Restructuring and Impairment Charges - Summary of Restructuring Accruals and Certain Facility Closures (Details) - USD ($)	12 Months Ended
	Sep. 30, 2021	Sep. 30, 2020	Sep. 30, 2019
Restructuring Reserve [Roll Forward]
Beginning balance	$ 8,191,000	$ 1,378,000
Expense additions	7,956,000	11,768,000	$ 0
Cash payments	(8,291,000)	(3,577,000)
Accrual adjustments	0	(1,378,000)
Ending balance	7,856,000	8,191,000	1,378,000
Facilities charges
Restructuring Reserve [Roll Forward]
Beginning balance	0	1,378,000
Expense additions		0
Cash payments		0
Accrual adjustments		(1,378,000)
Ending balance		0	1,378,000
Employee separation
Restructuring Reserve [Roll Forward]
Beginning balance	8,191,000	0
Expense additions	7,956,000	11,768,000
Cash payments	(8,291,000)	(3,577,000)
Accrual adjustments	0	0
Ending balance	$ 7,856,000	8,191,000	$ 0
Accounting Standards Update 2016-02 | Facilities charges
Restructuring Reserve [Roll Forward]
Accrual adjustments		$ 1,400,000