Restructuring Expenses - Summary of Restructuring Accruals and Certain Facility Closures (Details) - USD ($)	12 Months Ended
Sep. 30, 2020	Sep. 30, 2019	Sep. 30, 2018
Restructuring Reserve [Roll Forward]
Beginning balance	$ 1,378,000
Expense additions	11,768,000	$ 0	$ 0
Cash payments	(3,577,000)
Accrual adjustments	(1,378,000)
Ending balance	8,191,000	1,378,000
Less: current portion	8,191,000	1,378,000	3,850,000
Non-current	0	0	1,378,000
Facilities charges
Restructuring Reserve [Roll Forward]
Beginning balance	1,378,000	5,228,000
Expense additions	0	0
Cash payments	0	(3,850,000)
Accrual adjustments	(1,378,000)	0
Ending balance	0	1,378,000	$ 5,228,000
Employee separation
Restructuring Reserve [Roll Forward]
Beginning balance	0
Expense additions	11,768,000
Cash payments	(3,577,000)
Accrual adjustments	0
Ending balance	8,191,000	$ 0
Accounting Standards Update 2016-02 \| Facilities charges
Restructuring Reserve [Roll Forward]
Accrual adjustments	$ 1,400,000

Amount of cash payments made as the result of exit or disposal activities. Excludes payments associated with a discontinued operation or an asset retirement obligation.

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Amount of expenses associated with exit or disposal activities pursuant to an authorized plan. Excludes expenses related to a discontinued operation or an asset retirement obligation.

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Carrying amount (including both current and noncurrent portions of the accrual) as of the balance sheet date pertaining to a specified type of cost associated with exit from or disposal of business activities or restructuring pursuant to a duly authorized plan.

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Amount of expense (reversal of expense) which increases (decreases) the restructuring reserve from an adjustment to a previously accrued restructuring liability.

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Carrying amount as of the balance sheet date of known and estimated obligations associated with exit from or disposal of business activities or restructurings pursuant to a duly authorized plan, which are expected to be paid in the next twelve months or in the normal operating cycle if longer. Costs of such activities include those for one-time termination benefits, termination of an operating lease or other contract, consolidating or closing facilities, relocating employees, and costs associated with an ongoing benefit arrangement, but excludes costs associated with the retirement of a long-lived asset.

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Carrying amount as of the balance sheet date of known and estimated costs associated with exit from or disposal of business activities or restructurings pursuant to a duly authorized plan, which are expected to be paid after one year or beyond the next operating cycle, if longer. Costs of such activities include those for one-time termination benefits, termination of an operating lease or other contract, consolidating or closing facilities, and relocating employees, and costs associated with an ongoing benefit arrangement, but excludes costs associated with the retirement of a long-lived asset.

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A roll forward is a reconciliation of a concept from the beginning of a period to the end of a period.

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