Debt (Term Facilities and Revolving Credit Facility) (Details) - USD ($)		12 Months Ended
	Apr. 01, 2021	Sep. 30, 2021	Sep. 30, 2020	Sep. 30, 2019	Sep. 30, 2018	Jun. 30, 2021
Line of Credit Facility [Line Items]
Unamortized discount (premium) and debt issuance costs, net	$ 2,375,000	$ 11,738,000	$ 9,436,000
Line of credit facility, remaining borrowing capacity		60,000,000	45,000,000
Write off of deferred debt issuance cost		1,333,000	1,795,000		$ 0
Debt instrument, unused borrowing capacity, amount		49,888,000	32,037,000
Long-term debt, gross		754,943,000	885,470,000
Borrowings under credit facility		0	2,597,000	$ 292,825,000
2014 Revolving Credit Facility
Line of Credit Facility [Line Items]
Line of credit facility, remaining borrowing capacity		350,000,000	125,000,000
Borrowings under credit facility	105,000,000
Letter of Credit
Line of Credit Facility [Line Items]
Letters of credit outstanding, amount		10,112,000	12,963,000
Debt instrument, unused borrowing capacity, amount		302,888,000	112,037,000
2021 Credit Agreement | 2014 Revolving Credit Facility
Line of Credit Facility [Line Items]
Line of credit facility, maximum borrowing capacity	350,000,000
2021 Credit Agreement | Letter of Credit
Line of Credit Facility [Line Items]
Line of credit facility, maximum borrowing capacity	60,000,000
2014 Revolving Credit Facility
Line of Credit Facility [Line Items]
Long-term debt, gross		$ 0	0
Term Loan [Member]
Line of Credit Facility [Line Items]
Debt instrument, periodic payment, principal	1,188,000
Payments of Financing Costs	4,985,000
Proceeds from Issuance of Secured Debt	475,000,000
Term Loan [Member] | 2021 Credit Agreement
Line of Credit Facility [Line Items]
Debt Instrument, Face Amount	$ 475,000,000
2021 Term Loan
Line of Credit Facility [Line Items]
Debt instrument, basis spread on variable rate		2.50%
Long-term debt, gross		$ 473,837,000	0			$ 814,538,000
Interest Payable, Current		$ 25,000
Debt instrument, interest rate,		2.63%
2021 Term Loan | LIBOR
Line of Credit Facility [Line Items]
Debt instrument, basis spread on variable rate		0.13%
2021 Revolving Credit Facility, due April 2026
Line of Credit Facility [Line Items]
Debt instrument, basis spread on variable rate		2.25%
Long-term debt, gross		$ 37,268,000	0
Interest Payable, Current		$ 268,000
Debt instrument, interest rate,		2.38%
2021 Revolving Credit Facility, due April 2026 | LIBOR
Line of Credit Facility [Line Items]
Debt instrument, basis spread on variable rate		0.13%
Securitization Facility, due April 1, 2024
Line of Credit Facility [Line Items]
Long-term debt, gross		$ 150,061,000	$ 0
Accrued interest		$ 61,000