Commitments and Contingencies (Details) (USD $)	0 Months Ended			12 Months Ended
	May 02, 2014	Jan. 25, 2013	Dec. 09, 2011	Sep. 30, 2014	Sep. 30, 2014 Mid-Tex Division [Member]	Sep. 30, 2013 Mid-Tex Division [Member]	Sep. 30, 2012 Mid-Tex Division [Member]	Sep. 30, 2014 Nonregulated Segment [Member]	Sep. 30, 2013 Nonregulated Segment [Member]	Sep. 30, 2012 Nonregulated Segment [Member]	Sep. 30, 2014 Inventories Under Indexed Contracts [Member] Mid-Tex Division [Member] MMcf	Sep. 30, 2014 Inventories Under Indexed Contracts [Member] Nonregulated Segment [Member] MMcf	Sep. 30, 2014 Inventories Under Fixed Price Contracts [Member] Nonregulated Segment [Member] MMcf
Loss Contingency Information About Litigation Matters [Abstract]
Description of Pending Litigation				Beginning in April 2009, Atmos Energy and two subsidiaries of AEH, Atmos Energy Marketing, LLC (AEM) and Atmos Gathering Company, LLC (AGC) (collectively, the Atmos Entities), were 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 October 17, 2011, we filed our brief of appellants with the Kentucky Court of Appeals (Court), appealing the verdict of the trial court. The appellees in this case subsequently filed their appellees’ brief with the Court on January 16, 2012, with our reply brief being filed with the Court on March 19, 2012. Oral arguments were held in the case on August 27, 2012. In an opinion handed down on January 25, 2013, the Court of Appeals overturned the $28.5 million jury verdict returned against the Atmos Entities. In a unanimous decision by a three-judge panel, the Court of Appeals reversed the claims asserted by the landowners and investors/working interest owners. The Court of Appeals concluded that all of such claims that the Atmos Entities appealed should have been dismissed by the trial court as a matter of law. The Court of Appeals let stand the jury verdict on one claim that Atmos Energy and our subsidiaries chose not to appeal, which was a trespass claim. The jury had awarded a total of $10,000 in compensatory damages to one landowner on that claim. The Court of Appeals vacated all of the other damages awarded by the jury and remanded the case to the trial court for a new trial, solely on the issue of whether punitive damages should be awarded to that landowner and, if so, in what amount.The investors/working interest owners, on February 25, 2013, and the landowners, on March 19, 2013, each filed with the Supreme Court of Kentucky, separate motions for discretionary review of the opinion of the Court of Appeals. We filed a response to the motion filed by the investors/working owners on March 27, 2013 and to the landowners’ motion on April 17, 2013. The Kentucky Supreme Court denied the motions for discretionary review on February 12, 2014 and the decision of the Court of Appeals became final on February 21, 2014.  We had previously accrued what we believed to be an adequate amount for the anticipated resolution of this matter. This accrual was reversed during the second fiscal quarter of fiscal 2014 as the appellate process in this case had been completed. Atmos Energy had also filed a motion with the trial court, the Circuit Court of Edmonson County, Kentucky, on March 10, 2014, seeking a ruling that the remaining landowner was not entitled to any punitive damages on the sole remaining claim of trespass.  On May 19, 2014, the Edmonson County Circuit Court entered judgment dismissing any claim for punitive damages relating to the trespass claim. There was no appeal of this judgment. The lawsuit in Edmonson County has now been fully resolved.In addition, in a related matter, on July 12, 2011, the Atmos Entities filed a lawsuit in the United States District Court, Western District of Kentucky, Atmos Energy Corporation et al.vs. Resource Energy Technologies, LLC and Robert Thorpe and John F. Charles, 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 about $3.5 million, plus interest that continues to accrue. 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. The defendants filed a motion to dismiss the case on August 25, 2011, with Atmos Energy filing a brief in response to such motion on September 19, 2011. On March 27, 2012 the court denied the motion to dismiss. Atmos Energy filed a motion for partial summary judgment against the defendants with the District Court on July 15, 2014 and filed an Amended Complaint on July 18, 2014. On August 28, 2014, the court entered an order authorizing the withdrawal of the lawyer representing the estate of Robert Thorpe, giving the Thorpe Estate until October 2, 2014 to engage a new lawyer. On September 29, 2014, Resource Energy Technologies, LLC and John Charles, individually, entered into an agreed-upon judgment in favor of the Atmos Entities in the amount of $3.6 million, which resolved all claims by the Atmos Entities against those defendants and which dismissed with prejudice all counterclaims against the Atmos Entities. That judgment was settled with the Atmos Entities for $15,000, based on information obtained in discovery that showed those defendants lacked the ability to pay. The only claims remaining in the case are the Atmos Entities’ claims against the Thorpe Estate. The Thorpe Estate has not responded to the motion for partial summary judgment or the amended complaint. In a hearing held on October 7, 2014, the court was advised that the Thorpe Estate was insolvent and without funds to hire another attorney. The court has entered an order to show cause setting the case for a hearing on December 3, 2014 and indicated that if the Thorpe Estate fails to appear, an order of default will be entered.
Loss Contingency, Compensatory Damages Awarded, Value		$ 10,000
Litigation Settlement, Amount				3,600,000
Litigation Settlement, Judgment Amount Settled				15,000
Business License Tax [Abstract]
Business License Tax Examination, Description				Atmos Energy, through its affiliate, AEM, has been involved in a dispute with the Tennessee Department of Revenue (TDOR) regarding sales business tax audits over a period of several years. The cumulative assessment approximated $12 million as of March 31, 2014, which AEM challenged. We had previously accrued in prior years what we believed to be an adequate amount for the anticipated resolution of this matter. With respect to certain issues, AEM and the TDOR filed competing Partial Motions for Summary Judgment with the Chancery Court. On August 2, 2013, the Chancery Court granted the TDOR's Partial Motion for Summary Judgment and denied AEM's Partial Motion for Summary Judgment. An agreed order of dismissal with prejudice between AEM and TDOR was approved by the Chancery Court and entered on May 2, 2014, whereby AEM agreed to pay $6.2 million to TDOR to resolve all business tax-related liabilities outstanding through September 2014. The State of Tennessee also passed related legislation, effective July 1, 2014, that should help minimize any disputes over this type of sales business tax in the future.
Business License Tax Examination, Settlement Amount	6,200,000
Long Term Purchase Commitment [Line Items]
Long Term Purchase Commitment Minimum Quantity Required Within One Year											49,700	111,500	7,800
Long Term Purchase Commitment Minimum Quantity Required One To Three Years											69,800	19,800
Long Term Purchase Commitment Minimum Quantity Required After Three Years												500
Purchase Commitment Amount Minimum													1.96
Purchase Commitment Amount Maximum													4.49
Significant Purchase Commitment, Amount					140,900,000	89,000,000	72,200,000	1,687,500,000	1,246,100,000	978,800,000
Estimated Contractual Demand Fees [Abstract]
2015				7,426,000
2016				2,117,000
2017				1,437,000
2018				773,000
2019				143,000
Thereafter				214,000
Total Estimated Contractual Demand Fees				12,110,000
Loss Contingency, Settlement [Abstract]
Loss Contingency, Civil Penalty Paid to United States Treasury			6,400,000
Loss Contingency, Civil Penalty Paid to Energy Assistance Programs			$ 5,600,000