Debt - Summary of Long-term Debt (Detail) - USD ($) $ in Thousands	Mar. 31, 2022	Sep. 30, 2021
Debt Instrument [Line Items]
Long-term debt	$ 1,264,275
Less: Current portion of long-term debt and other borrowings	(46,500)	$ (12,500)
Long-term debt, less current portion	1,218,235	984,818
Long-term Debt
Debt Instrument [Line Items]
Long-term debt	1,264,735	997,318
Total borrowings	1,295,775	1,020,525
Deferred financing costs	(19,768)	(17,692)
Original issue discount	(11,272)	(5,515)
Less: Current portion of long-term debt and other borrowings	(46,500)	(12,500)
Long-term debt, less current portion	1,218,235	984,818
Long-term Debt \| Secured Credit Facility Term Loan, due October 2027
Debt Instrument [Line Items]
Long-term debt	1,014,275	1,020,525
Long-term Debt \| Secured Credit Facility Incremental Term Loan, due October 2027
Debt Instrument [Line Items]
Long-term debt	250,000	0
Long-term Debt \| Secured Credit Facility Revolving Loan
Debt Instrument [Line Items]
Long-term debt	$ 31,500	$ 0

Amount, before unamortized (discount) premium and debt issuance costs, of long-term debt. Includes, but is not limited to, notes payable, bonds payable, commercial loans, mortgage loans, convertible debt, subordinated debt and other types of debt.

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Amount, after accumulated amortization, of debt discount.

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Amount, after unamortized (discount) premium and debt issuance costs, of long-term debt. Includes, but not limited to, notes payable, bonds payable, debentures, mortgage loans and commercial paper. Excludes capital lease obligations.

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Amount, after unamortized (discount) premium and debt issuance costs, of long-term debt, classified as current. Includes, but not limited to, notes payable, bonds payable, debentures, mortgage loans and commercial paper. Excludes capital lease obligations.

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Amount after unamortized (discount) premium and debt issuance costs of long-term debt classified as noncurrent and excluding amounts to be repaid within one year or the normal operating cycle, if longer. Includes, but not limited to, notes payable, bonds payable, debentures, mortgage loans and commercial paper. Excludes capital lease obligations.

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The remaining balance of debt issuance expenses that were capitalized and are being amortized against income over the lives of the respective bond issues. This does not include the amounts capitalized as part of the cost of the utility plant or asset.

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