Leases - Narrative (Details) $ in Thousands	12 Months Ended
	Sep. 30, 2020 USD ($) ft²	Oct. 01, 2019 USD ($)	Sep. 30, 2019 USD ($)
Lessee, Lease, Description [Line Items]
Operating lease right-of-use assets	$ 300,680		$ 0
Operating Lease, Impairment Loss	9,700
Sublease Income	10,200
Lessor, Operating Lease, Payments to be Received, Next Twelve Months	4,500
Lessor, Operating Lease, Payments to be Received, Two To Three Years	$ 5,700
Office Building [Member]
Lessee, Lease, Description [Line Items]
Operating Lease, Number of Square Feet | ft²	515,000
Accounting Standards Update 2016-02 [Member]
Lessee, Lease, Description [Line Items]
Operating lease right-of-use assets		$ 304,800
Lease Liabilities		$ 386,400