Document and Entity Information (USD $)	12 Months Ended
	Sep. 30, 2012	Nov. 06, 2012	Mar. 31, 2012
Top Element 00100 Document Document And Entity Information [Abstract]
Document Type	10-K
Document Period End Date	Sep. 30, 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	2012
Document Fiscal Period Focus	FY
Entity Common Stock Shares Outstanding		90,240,464
Entity Public Float			$ 2,764,486,845