Document and Entity Information (USD $)	3 Months Ended
	Dec. 31, 2012	Feb. 01, 2013	Mar. 31, 2012
Document And Entity Information [Abstract]
Document Type	10-Q
Document Period End Date	Dec. 31, 2012
Amendment Flag	false
Entity Registrant Name	Atmos Energy Corporation
Entity Central Index Key	0000731802
Entity Current Reporting Status	Yes
Entity Voluntary Filers	No
Current Fiscal Year End Date	--09-30
Entity Filer Category	Large Accelerated Filer
Entity Well Known Seasoned Issuer	Yes
Document Fiscal Year Focus	2013
Document Fiscal Period Focus	Q1
Entity Common Stock Shares Outstanding		90,517,509
Entity Public Float			$ 2,764,486,845