Long-Term Debt (Details) - USD ($) $ in Thousands		12 Months Ended
	Oct. 21, 2019	Sep. 30, 2021	Sep. 30, 2020	Sep. 30, 2019
Debt Instrument
Debt, long-term and short-term, combined amount, total		$ 609,900	$ 703,700
Current portion of long-term debt		(116,300)	(63,800)
Unamortized debt issuance expense		(4,700)	(6,600)
Unamortized debt discount	$ (14,000)	(7,700)	(10,700)
Long-term debt		481,200	622,600
Payments of debt issuance costs and deferred financing fees	(9,600)	0	(9,600)	$ 0
Proceeds from debt, net of discount and issuance costs	776,400
Loss on refinancing of debt		1,600	0	$ 0
Long-Term Debt, Maturity, Year One		116,300
Long-Term Debt, Maturity, Year Two		35,000
Long-Term Debt, Maturity, Year Three		35,000
Long-Term Debt, Maturity, Year Four		423,600
Long-Term Debt, Maturity, Year Five		0
Estimated future interest payments on debt		72,900
Estimated future interest payments on debt, next 12 months		26,200
Bridge Loan
Debt Instrument
Proceeds from issuance of long-term debt		1,225,000
Repayments of Debt		(1,225,000)
Interest costs incurred		2,200
Term Loan
Debt Instrument
Debt, long-term and short-term, combined amount, total		609,900	673,700
Proceeds from issuance of long-term debt	$ 700,000
Discount percentage on debt instrument	98.00%
Periodic payment of long-term debt principal		8,750
Excess cash flow prepayment		81,300	28,800
Letter of Credit
Debt Instrument
Maximum borrowing capacity on line of credit		20,000
Revolving Credit Facility
Debt Instrument
Debt, long-term and short-term, combined amount, total		0	30,000
Maximum borrowing capacity on line of credit		200,000
Proceeds from issuance of long-term debt	$ 100,000
Proceeds from borrowing under line of credit		20,000	195,000
Repayments of lines of credit	$ (20,000)	(50,000)	(165,000)
Remaining borrowing capacity on line of credit		200,000	$ 170,000
Letters of credit outstanding, amount		0
Debt covenant, maximum undischarged judgments		$ 65,000