Aggregate notional amount specified by the derivative(s). Expressed as an absolute value.

Reference 1: http://www.xbrl.org/2003/role/presentationRef
-Publisher SEC
-Name Regulation S-X (SX)
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Maximum length of time hedged in price risk cash flow hedges.

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Settlement on Derivative Instruments

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Percentage points added to the reference rate to compute the variable rate on the debt instrument.

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Face (par) amount of debt instrument at time of issuance.

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Line items represent financial concepts included in a table. These concepts are used to disclose reportable information associated with domain members defined in one or many axes to the table.

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Nominal energy measure used to calculate payments on a derivative instrument.

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- Definition

The estimated net amount of unrealized gains or losses on interest rate cash flow hedges as of the balance sheet date expected to be reclassified to earnings within the next twelve months.

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Amount of cash and cash equivalents restricted as to withdrawal or usage, classified as current. Cash includes, but is not limited to, currency on hand, demand deposits with banks or financial institutions, and other accounts with general characteristics of demand deposits. Cash equivalents include, but are not limited to, short-term, highly liquid investments that are both readily convertible to known amounts of cash and so near their maturity that they present insignificant risk of changes in value because of changes in interest rates.

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Derivative Instruments and Hedging Activities - Additional Information (Details) MMBTU in Millions			12 Months Ended
	Oct. 31, 2017 USD ($)	Mar. 31, 2016 USD ($)	Sep. 30, 2018 USD ($) MMBTU	Sep. 30, 2017 USD ($) MMBTU	Sep. 30, 2016 USD ($)
Derivative
Settlement of interest rate protection agreements		$ 35,975,000	$ 0	$ 0	$ (35,975,000)
Interest rate cash flow hedge loss to be reclassified during next 12 months, net			3,485,000
Restricted cash in brokerage accounts			1,190,000	3,046,000
Interest Rate Protection Agreements
Derivative
Underlying variable rate debt			$ 0	$ 0
Gas Utility
Derivative
Notional amount (in units) \| MMBTU			23.2	14.8
Maximum length of time hedged in price risk cash flow hedges (in months)			13 months
Unsecured Debt
Derivative
Aggregate principal amount	$ 125,000,000
Debt Instrument, Basis Spread on Variable Rate	3.00%
Interest Rate Swap Agreement
Derivative
Aggregate principal amount	$ 114,063,000
Maximum \| Unsecured Debt
Derivative
Debt Instrument, Basis Spread on Variable Rate	1.875%