Leases - Components of lease expense (Details) - USD ($) $ in Thousands	12 Months Ended
	Sep. 30, 2021	Sep. 30, 2020	Oct. 01, 2019
New Accounting Pronouncements and Changes in Accounting
(Accumulated deficits) / Retained earnings	$ (504,126)	$ 174,248
Operating lease cost
Operating lease cost	186,500	191,600
Finance lease cost:
Amortization of right-of-use assets	13,000	17,100
Interest on lease liabilities	2,000	1,900
Variable lease cost	35,500	36,500
Total lease cost	$ 237,000	$ 247,100
ASU 2016-02
New Accounting Pronouncements and Changes in Accounting
(Accumulated deficits) / Retained earnings			$ 87,800