Leases - Additional Information (Details) $ in Thousands	1 Months Ended	3 Months Ended		12 Months Ended
	Dec. 31, 2014 USD ($)	Sep. 30, 2020 USD ($)	Mar. 31, 2015 USD ($)	Sep. 30, 2021 USD ($) extension_option	Sep. 30, 2020 USD ($)	Sep. 30, 2018	Sep. 30, 2017 USD ($)	Sep. 30, 2016 USD ($)
Lessee, Lease, Description [Line Items]
Weighted average remaining lease term for operating leases (in years)				5 years 29 days
Weighted average incremental borrowing rate used to measure lease liabilities				5.92%
Initial term of lease (in years)				10 years
Estimated minimum future rental payments				$ 260,299
Impairment charges		$ 5,000
Operating lease right of use asset non cash				62,800	$ 62,800
Operating lease liability non cash				$ 29,200	$ 29,200
Corporate Office Lease, Two Five-Year Extension Options
Lessee, Lease, Description [Line Items]
Initial term of lease (in years)	13 years
Annual rent at lease inception	$ 2,500
Annual rent in the terminal year of lease	$ 3,900
Number of extension options | extension_option				2
Renewable term of lease (in years)				5 years
Estimated minimum future rental payments				$ 27,900
Estimated future minimum sublease payments							$ 12,200	$ 12,200
Initial leased premises surrendered						15.00%
Regional Offices Sublease
Lessee, Lease, Description [Line Items]
Estimated future minimum sublease payments			$ 2,900
Sublease term (in years)			9 years