Long-Term Debt (Details) - USD ($) $ in Thousands		12 Months Ended
	Oct. 21, 2019	Sep. 30, 2020	Sep. 30, 2019	Sep. 30, 2018
Debt Instrument
Debt, long-term and short-term, combined amount, total		$ 703,700
Current portion of long-term debt		(63,800)	$ 0
Unamortized debt issuance expense		(6,600)
Unamortized debt discount	$ (14,000)	(10,700)
Long-term debt		622,600
Payments of debt issuance costs and deferred financing fees	(9,600)	(9,600)	$ 0	$ 0
Proceeds from debt, net of discount and issuance costs	776,400
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		673,700
Proceeds from issuance of long-term debt	700,000
Periodic payment of long-term debt principal		8,750
Excess cash flow prepayment		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		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		195,000
Repayments of lines of credit	$ (20,000)	(165,000)
Remaining borrowing capacity on line of credit		170,000
Letters of credit outstanding, amount		0
Debt covenant, maximum undischarged judgments		$ 65,000