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Leases - Additional Information (Details)
 12 Months Ended
Sep. 30, 2021
USD ($)
ft²
Sep. 30, 2020
USD ($)
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  
Operating right-of-use lease assets 152,337,000 $ 149,933,000
Operating lease, liability 208,799,000  
Lease Cost    
Operating cash flows from operating leases 50,299,000  
Facility Closures and Related Costs    
Lessee Lease Description [Line Items]    
Operating lease liability, net. restructured facilities 3,600,000 $ 11,300,000
Operating right-of-use lease assets 1,200,000  
Operating lease, liability 4,800,000  
Lease Cost    
Operating cash flows from operating leases 7,800,000  
Facility Closures and Related Costs | Prior Headquarters    
Lessee Lease Description [Line Items]    
Operating lease, impairment loss 100,000  
Facility Closures and Related Costs | Operating Lease Short Term Lease Obligation    
Lessee Lease Description [Line Items]    
Operating lease, liability 4,200,000  
Facility Closures and Related Costs | Operating Lease Long Term Lease Obligation    
Lessee Lease Description [Line Items]    
Operating lease, liability 600,000  
Sublease Income Committed    
Lessee Lease Description [Line Items]    
Sublease income assumed 1,200,000  
Sublease Income Estimated Uncommitted    
Lessee Lease Description [Line Items]    
Sublease income assumed $ 0