Financial Instruments Descriptions (Details) $ in Millions	6 Months Ended
Mar. 31, 2018 USD ($) MMcf
General Discussion Of Derivative Instruments And Hedging Activities [Abstract]
Minimum Hedge Percentage Of Anticipated Heating Season Gas	25.00%
Maximum Hedge Percentage Of Anticipated Heating Season Gas	50.00%
Hedge Percentage Of Anticipated Heating Season Gas	26.00%
Hedge Volume Of Anticipated Heating Season Gas \| MMcf	15,000
Accumulated Other Comprehensive Income (Loss), Derivatives Qualifying as Hedges, Interest Rate Agreements, Realized Gain (Loss), Net of Tax	$ (49.1)
Interest Rate Hedges, Senior Notes 2019 Issuance [Member]
Derivative [Line Items]
Notional Amount of Interest Rate Cash Flow Hedge Derivatives	450.0
Anticipated Debt Issuance, Amount	$ 450.0
Derivative, Average Forward Interest Rate	3.78%

- Definition

Net realized gains and losses in accumulated other comprehensive income from interest rate agreements designated and qualifying as the effective portion of cash flow hedges.

+ References

No definition available.

+ Details

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- Definition

Anticipated debt issuance amount of future debt issuance.

+ References

No definition available.

+ Details

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- Definition

Anticipated percentage of heating season gas purchases using financial instruments.

+ References

No definition available.

+ Details

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- Definition

Anticipated volume of heating season gas purchases using financial instruments.

+ References

No definition available.

+ Details

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- Definition

Maximum anticipated percentage of heating season gas purchases hedged using financial instruments.

+ References

No definition available.

+ Details

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- Definition

Minimum anticipated percentage of heating season gas purchases hedged using financial instruments.

+ References

No definition available.

+ Details

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- Definition

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

+ References

Reference 1: http://www.xbrl.org/2003/role/presentationRef
-Publisher SEC
-Name Regulation S-X (SX)
-Number 210
-Article 12
-Section 13
-Sentence Column B

+ Details

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- Definition

Average stated rate on a group of interest rate forward or futures contracts.

+ References

No definition available.

+ Details

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- Definition

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.

+ References

No definition available.

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- References

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