Details of Selected Consolidated Balance Sheet Captions - Other Current Liabilities Detail Table (Details) - USD ($) $ in Thousands	Sep. 30, 2020	Sep. 30, 2019
Balance Sheet Related Disclosures [Abstract]
Customer credit balances and deposits	$ 56,485	$ 54,617
Accrued employee costs	57,057	55,216
Deferred gas costs	19,985	14,112
Operating leases	35,716
Accrued interest	53,554	51,381
Liabilities from risk management activities	2,015	4,552
Taxes payable	148,292	135,597
Pension and postretirement liabilities	29,609	26,197
Regulatory cost of service reserve	1,716	4,209
Regulatory cost of removal obligation	73,908	55,721
APT annual adjustment mechanism, current	43,893	52,856
Regulatory excess deferred taxes	20,887	21,206
Other	3,344	3,837
Total	$ 546,461	$ 479,501

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Aggregate carrying amount, as of the balance sheet date, of current obligations not separately disclosed in the balance sheet or other current liabilities table. Current liabilities are expected to be paid within one year (or the normal operating cycle, if longer).

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Rate action of a regulator resulting in capitalization or accrual of over-recovered regulatory clause revenue. This is the current portion of the liability.

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Carrying value as of the balance sheet date of obligations to remove certain regulated fixed assets from service. Used to reflect the current portion of the liabilities (due within one year or within the normal operating cycle if longer).

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Amount of obligation to transfer good or service to customer for which consideration has been received or is receivable, classified as current.

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Carrying value as of the balance sheet date of [accrued] interest payable on all forms of debt, including trade payables, that has been incurred and is unpaid. Used to reflect the current portion of the liabilities (due within one year or within the normal operating cycle if longer).

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Present value of lessee's discounted obligation for lease payments from operating lease, classified as current.

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Gas costs of a regulated entity that are refundable through future rate adjustments. Such costs are a form of a regulatory liabilities and are expected to be refunded in less than one year through rate adjustments.

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Carrying value as of the balance sheet date of obligations incurred and payable for statutory income, sales, use, payroll, excise, real, property and other taxes. Used to reflect the current portion of the liabilities (due within one year or within the normal operating cycle if longer).

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