Supplemental Cash Flow Information - Supplemental Disclosure of Non-cash Activity (Details) - USD ($) $ in Thousands	6 Months Ended
	Mar. 31, 2021	Mar. 31, 2020	Sep. 30, 2020	Oct. 01, 2019
Cash and Cash Equivalents [Line Items]
Operating lease right-of-use assets	$ 12,719		$ 13,103
Operating lease liabilities	14,603		15,333
Increase in operating lease right-of-use assets	1,453	$ 3,064
Increase in operating lease liabilities	1,453	3,064
Supplemental disclosure of cash activity:
Interest payments	37,412	28,731
Income tax payments	143	2
Tax refunds received	49	315
Reconciliation of cash, cash equivalents, and restricted cash:
Cash and cash equivalents	355,533	294,265	327,693
Restricted cash	18,162	18,282	$ 14,835
Total cash, cash equivalents, and restricted cash shown in the statement of cash flows	373,695	312,547
Accounting Standards Update 2016-02
Cash and Cash Equivalents [Line Items]
Operating lease right-of-use assets	0	13,895		$ 13,900
Operating lease liabilities	$ 0	$ 16,028		$ 16,000