Short-term Borrowings and Long-term Debt - ABL Facility and Canadian Sub-Facility (Details) - USD ($)	3 Months Ended	6 Months Ended
	Mar. 31, 2021	Mar. 31, 2021	Mar. 31, 2020
Debt Instruments
Remaining aggregate outstanding principal amount paid		$ 213,271,000	$ 437,385,000
Loss on extinguishment of debt from write-off of unamortized deferred financing costs		(1,390,000)	$ 357,000
Term Loan B
Debt Instruments
Remaining aggregate outstanding principal amount paid	$ 213,200,000
Loss on extinguishment of debt from write-off of unamortized deferred financing costs	(1,400,000)
ABL facility
Debt Instruments
Outstanding borrowing	0	0
Revolving credit facility	$ 496,900,000	$ 496,900,000
Debt instrument, maturity date		Jul. 06, 2022