Commitments and Contingencies (Details) (USD $)	12 Months Ended
	Sep. 30, 2011	Sep. 30, 2010	Sep. 30, 2009
Loss Contingency Information About Litigation Matters Abstract
Description of Pending Litigation	Since April 2009, Atmos Energy and two subsidiaries of AEH, AEM and Atmos Gathering Company, LLC (AGC) (collectively, the Atmos Entities), have been involved in a lawsuit filed in the Circuit Court of Edmonson County, Kentucky related to our Park City Gathering Project. The dispute which gave rise to the litigation involves the amount of royalties due from a third party producer to landowners (who own the mineral rights) for natural gas produced from the landowners’ properties. The third party producer was operating pursuant to leases between the landowners and certain investors/working interest owners. The third party producer filed a petition in bankruptcy, which was subsequently dismissed due to the lack of meaningful assets to reorganize or liquidate. Although certain Atmos Energy companies entered into contracts with the third party producer to gather, treat and ultimately sell natural gas produced from the landowners’ properties, no Atmos Energy company had a contractual relationship with the landowners or the investors/working interest owners. After the lawsuit was filed, the landowners were successful in terminating for non-payment of royalties the leases related to the production of natural gas from their properties. Subsequent to termination, the investors/working interest owners under such leases filed additional claims against us for the termination of the leases. During the trial, the landowners and the investors/working interest owners requested an award of compensatory damages plus punitive damages against us. On December 17, 2010, the jury returned a verdict in favor of the landowners and investor/working interest owners and awarded compensatory damages of $3.8 million and punitive damages of $27.5 million payable by Atmos Energy and the two AEH subsidiaries. A hearing was held on February 28, 2011 to hear a number of motions, including a motion to dismiss the jury verdict and a motion for a new trial. The motions to dismiss the jury verdict and for a new trial were denied. However, the total punitive damages award was reduced from $27.5 million to $24.7 million. On March 30, 2011, we filed a notice of appeal of this ruling. We strongly believe that the trial court erred in not granting our motion to dismiss the lawsuit prior to trial and that the verdict is unsupported by law. After consultation with counsel, we believe that it is probable that any judgment based on this verdict will be overturned on appeal. In addition, in a related development, on July 12, 2011, the Atmos Entities filed a lawsuit in the United States District Court, Western District of Kentucky against the third party producer and its affiliates to recover all costs, including attorneys’ fees, incurred by the Atmos Entities, which are associated with the defense and appeal of the case discussed above as well as for all damages awarded to the plaintiffs in such case against the Atmos Entities. The total amount of damages being claimed in the lawsuit is “open-ended” since the appellate process and related costs are ongoing. This lawsuit is based upon the indemnification provisions agreed to by the third party producer in favor of Atmos Gathering that are contained in an agreement entered into between Atmos Gathering and the third party producer in May 2009. We have accrued what we believe is an adequate amount for the anticipated resolution of this matter; however, the amount accrued is less than the amount of the verdict. The Company does not have insurance coverage that could mitigate any losses that may arise from the resolution of this matter; however, we believe that the final outcome will not have a material adverse effect on our financial condition, results of operations or cash flows.
Long Term Purchase Commitment [Line Items]
Purchase Commitment Amount Maximum	$ 6.36
Long Term Commitment Purchases Abstract
Significant Purchase Commitment Amount Description	1,498,600,000	1,562,800,000	1,484,500,000
Long Term Purchase Commitment Abstract
Significant Purchase Commitment Remaining Minimum Amount Committed Next Fiscal Year	274,985,000
Significant Purchase Commitment Remaining Minimum Amount Committed Second Fiscal Year	102,959,000
Significant Purchase Commitment Remaining Minimum Amount Committed Third Fiscal Year	82,235,000
Significant Purchase Commitment Remaining Minimum Amount Committed Fourth Fiscal Year	0
Significant Purchase Commitment Remaining Minimum Amount Committed Fifth Fiscal Year	0
Significant Purchase Commitment Remaining Minimum Amount Committed Thereafter	0
Total Estimated Purchase Commitments	460,179,000
Estimated Contractual Demand Fees [Abstract]
Contractual Demand Fees, Demand Fees Due Next Fiscal Year	25,362,000
Contractual Demand Fees, Demand Fees Due Second Fiscal Year	16,711,000
Contractual Demand Fees, Demand Fees Due Third Fiscal Year	9,988,000
Contractual Demand Fees, Demand Fees Due Fourth Fiscal Year	4,130,000
Contractual Demand Fees, Demand Fees Due Fifth Fiscal Year	278,000
Contractual Demand Fees, Demand Fees Due Thereafter	165,000
Total Estimated Contractual Demand Fees	56,634,000
Inventories Under Indexed Contracts [Member]
Long Term Purchase Commitment [Line Items]
Long Term Purchase Commitment Minimum Quantity Required Within One Year	103.3
Long Term Purchase Commitment Minimum Quantity Required One To Three Years	46.4
Long Term Purchase Commitment Minimum Quantity Required After Three Years	0.9
Inventories Under Fixed Price Contracts [Member]
Long Term Purchase Commitment [Line Items]
Long Term Purchase Commitment Minimum Quantity Required Within One Year	4.2
Long Term Purchase Commitment Minimum Quantity Required One To Three Years	0.3
Purchase Commitment Amount Minimum	$ 3.49