Supplemental Cash Flow Information - Supplemental Disclosure of Non-cash Activity (Details) - USD ($) $ in Thousands	9 Months Ended
	Jun. 30, 2021	Jun. 30, 2020	Sep. 30, 2020	Oct. 01, 2019	Sep. 30, 2019
Supplemental Cash Flow Elements [Abstract]
Operating lease right-of-use assets	$ 13,015		$ 13,103	$ 13,900	$ 13,895
Operating lease liabilities	14,813		15,333	$ 16,000	$ 16,028
Increase in operating lease right-of-use assets (b)	2,649	$ 3,097
Increase in operating lease liabilities (b)	2,649	3,097
Supplemental disclosure of cash activity:
Interest payments	63,878	60,678
Income tax payments	2,297	2
Tax refunds received	49	315
Reconciliation of cash, cash equivalents, and restricted cash:
Cash and cash equivalents	358,334	152,266	327,693
Restricted cash	24,690	13,086	$ 14,835
Total cash, cash equivalents, and restricted cash shown in the statement of cash flows	$ 383,024	$ 165,352