Fair Value Measurements (Details) (USD $)	12 Months Ended
Sep. 30, 2011	Sep. 30, 2010
Fair Value Abstract
Cash Collateral Right To Reclaim Cash	$ 28,800,000	$ 24,900,000
Debt Instrument Fair Value	2,560,945,000
Cash Held In Margin Accounts Offset Current Risk Management Liabilities	12,400,000	12,600,000
Cash Held In Margin Accounts Classified Current Risk Management Asset	16,400,000	12,300,000
Other Matters [Abstract]
Asset Impairment Charges Park City	11,000,000
Asset Impairment Charges Fort Necessity	19,300,000
Nonrecurring fair value measurement	6,000,000
Fair Value Inputs Level 1 [Member]
Fair Value Assets And Liabilities Measured On Recurring And Nonrecurring Basis [Line Items]
Natural gas distribution segment	0	0
Nonregulated Segement Derivative Assets	15,262,000	18,544,000
Total financial instruments	15,262,000	18,544,000
Hedged portion of gas stored underground	47,940,000	57,507,000
Available-for-sale Securities, Money Market Funds	0	0
Available For Sale Securities, Registered Investment Companies	36,444,000	40,967,000
Available For Sale Securities, Bonds	0
Fair value	36,444,000	40,967,000
Total assets	99,646,000	117,018,000
Natural gas distribution segment	0	0
Nonregulated Segement Derivative Liabilities	22,091,000	41,430,000
Total liabilities	22,091,000	41,430,000
Fair Value Inputs Level 2 [Member]
Fair Value Assets And Liabilities Measured On Recurring And Nonrecurring Basis [Line Items]
Natural gas distribution segment	1,841,000	2,266,000
Nonregulated Segement Derivative Assets	97,396,000	42,462,000
Total financial instruments	99,237,000	44,728,000
Hedged portion of gas stored underground	0	0
Available-for-sale Securities, Money Market Funds	1,823,000	499,000
Available For Sale Securities, Registered Investment Companies	0	0
Available For Sale Securities, Bonds	14,366,000
Fair value	16,189,000	499,000
Total assets	115,426,000	45,227,000
Natural gas distribution segment	81,118,000	51,866,000
Nonregulated Segement Derivative Liabilities	115,617,000	31,950,000
Total liabilities	196,735,000	83,816,000
Fair Value Inputs Level 3 [Member]
Fair Value Assets And Liabilities Measured On Recurring And Nonrecurring Basis [Line Items]
Natural gas distribution segment	0	0
Nonregulated Segement Derivative Assets	0	0
Total financial instruments	0	0
Hedged portion of gas stored underground	0	0
Available-for-sale Securities, Money Market Funds	0	0
Available For Sale Securities, Registered Investment Companies	0	0
Available For Sale Securities, Bonds	0
Fair value	0	0
Total assets	0	0
Natural gas distribution segment	0	0
Nonregulated Segement Derivative Liabilities	0	0
Total liabilities	0	0
Netting And Collateral [Member]
Fair Value Assets And Liabilities Measured On Recurring And Nonrecurring Basis [Line Items]
Natural gas distribution segment	0	0
Nonregulated Segement Derivative Assets	(95,156,000)	(41,760,000)
Total financial instruments	(95,156,000)	(41,760,000)
Hedged portion of gas stored underground	0	0
Available-for-sale Securities, Money Market Funds	0	0
Available For Sale Securities, Registered Investment Companies	0	0
Available For Sale Securities, Bonds	0
Fair value	0	0
Total assets	(95,156,000)	(41,760,000)
Natural gas distribution segment	0	0
Nonregulated Segement Derivative Liabilities	(123,943,000)	(66,649,000)
Total liabilities	$ (123,943,000)	$ (66,649,000)

The pretax charge against earnings resulting from the write down of the Fort Necessity storage assets from their carrying value to their fair value.

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The pretax charge against earnings resulting from the write down of the Park City natural gas gathering assets from their carrying value to their fair value.

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This element represents the aggregate of the assets reported on the balance sheet at period end measured at fair value by the entity. This element is intended to be used in connection with the fair value disclosures required in the footnote disclosures to the financial statements.

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For an unclassified balance sheet, this item represents money market funds categorized neither as held-to-maturity nor trading.

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The amount of the right to reclaim cash collateral under master netting arrangements that has been offset against net derivative instrument positions.

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ash held in margin accounts classified as current risk managment assets

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ash held in margin accounts used to offset current risk management liabilites under master netting agreements

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Fair values as of the balance sheet date of all assets resulting from contracts that meet the criteria of being accounted for as derivative instruments.

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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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Represents gas gathering assets reported on the balance sheet at period end measured at fair value on a nonrecurring basis.

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Fair value amount as of the balance sheet date of the hedged portion of natural gas stored underground in depleted gas reservoirs, aquifers, or salt caverns to meet seasonal and peak load demands, and also as insurance against unforeseen supply disruptions, and deemed to be a current asset because it is expected to be used within twelve months or in the normal operating cycle.

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This element represents the aggregate of the liabilities reported on the balance sheet at period end measured at fair value by the entity. This element is intended to be used in connection with the fair value disclosures required in the footnote disclosures to the financial statements.

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Fair values as of the balance sheet date of all assets resulting from contracts that meet the criteria of being accounted for as derivative instruments, for the natural gas distribution segment.

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Fair values as of the balance sheet date of all liabilities resulting from contracts that meet the criteria of being accounted for as derivative instruments, for the natural gas distribution segment.

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Fair values as of the balance sheet date of all assets resulting from contracts that meet the criteria of being accounted for as derivative instruments, for the nonregulated segment.

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Fair values as of the balance sheet date of all liabilities resulting from contracts that meet the criteria of being accounted for as derivative instruments, for the nonregulated segment.

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For an unclassified balance sheet, total of debt securities categorized neither as held-to-maturity nor trading. Such securities are reported at fair value; unrealized gains and losses of such securities are excluded from earnings and included in other comprehensive income, a separate component of shareholders' equity, unless the Available-for-sale Security is designated as a hedge or is determined to have had an other than temporary decline in fair value below its amortized cost basis. All or a portion of the unrealized holding gain or loss of an Available-for-sale Security that is designated as being hedged in a fair value hedge shall be recognized in earnings during the period of the hedge, as should other than temporary declines in fair value below costs basis.

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Reference 1: http://www.xbrl.org/2003/role/presentationRef

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-Name Statement of Financial Accounting Standard (FAS)

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For an unclassified balance sheet, this item represents equity securities categorized neither as held-to-maturity nor trading. Equity securities represent ownership interests or the right to acquire ownership interests in corporations and other legal entities which ownership interest is represented by shares of common or preferred stock (which is not mandatorily redeemable or redeemable at the option of the holder), convertible securities, stock rights, or stock warrants. Unrealized gains and losses related to Available-for-sale Securities are excluded from earnings and reported in a separate component of shareholders' equity (other comprehensive income), unless the Available-for-sale Security is designated as a hedge or is determined to have had an other than temporary decline in fair value below its amortized cost basis. All or a portion of the unrealized holding gain or loss of an Available-for-sale Security that is designated as being hedged in a fair value hedge shall be recognized in earnings during the period of the hedge, as should other than temporary declines in fair value below costs basis.

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This element represents the portion of the balance sheet assertion valued at fair value by the entity whether such amount is presented as a separate caption or as a parenthetical disclosure. Additionally, this element may be used in connection with the fair value disclosures required in the footnote disclosures to the financial statements. The element may be used in both the balance sheet and disclosure in the same submission. This item represents Available-for-sale Securities which consist of all investments in certain debt and equity securities neither classified as trading or held-to-maturity securities. A debt security represents a creditor relationship with an enterprise. Debt securities include, among other items, US Treasury securities, US government securities, municipal securities, corporate bonds, convertible debt, commercial paper, and all securitized debt instruments. An equity security represents an ownership interest in an enterprise or the right to acquire or dispose of an ownership interest in an enterprise at fixed or determinable prices. Equity securities include, among other things, common stock, certain preferred stock, warrant rights, call options, and put options, but do not include convertible debt. An entity may opt to provide the reader with additional narrative text to better understand the nature of investments in debt and equity securities which are categorized as Available-for-sale.

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Estimated fair value of the debt instrument at the balance-sheet date.

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