Leases - Additional Information (Details)	3 Months Ended
	Dec. 31, 2020 USD ($) ft²	Dec. 28, 2019 USD ($)	Sep. 30, 2020 USD ($)	Feb. 28, 2019 USD ($)
Lessee Lease Description [Line Items]
Boston Lease Square Feet | ft²	250,000
Boston lease year one payments	$ 11,000,000.0
Boston lease per square foot annual increase	1
Boston lease annual increase	300,000
Boston lease building operating cost amount estimate year one	7,100,000
Boston lease leasehold improvement allowance	25,000,000
Boston lease leasehold improvement allowance per square foot	100
Payments to be received as sublease income				$ 9,100,000
Operating right-of-use lease assets	145,252,000		$ 149,933,000
Operating lease, liability	206,446,000
Lease Cost
Operating cash flows from operating leases	14,060,000	$ 5,498,000
Facility Closures and Related Costs
Lessee Lease Description [Line Items]
Operating lease liability, net. restructured facilities	7,600,000		$ 11,300,000
Operating right-of-use lease assets	2,600,000
Operating lease, liability	10,200,000
Lease Cost
Operating cash flows from operating leases	3,800,000	$ 2,400,000
Facility Closures and Related Costs | Operating Lease Short Term Lease Obligation
Lessee Lease Description [Line Items]
Operating lease, liability	6,600,000
Facility Closures and Related Costs | Operating Lease Long Term Lease Obligation
Lessee Lease Description [Line Items]
Operating lease, liability	3,600,000
Sublease Income Committed
Lessee Lease Description [Line Items]
Sublease income assumed	2,300,000
Sublease Income Estimated Uncommitted
Lessee Lease Description [Line Items]
Sublease income assumed	$ 300,000