Document And Entity Information (USD $)	12 Months Ended
	Aug. 31, 2012	Oct. 15, 2012	Feb. 29, 2012
Document And Entity Information [Abstract]
Document Type	10-K
Amendment Flag	false
Document Period End Date	Aug. 31, 2012
Document Fiscal Year Focus	2012
Document Fiscal Period Focus	FY
Entity Registrant Name	SONIC CORP
Entity Central Index Key	0000868611
Current Fiscal Year End Date	--08-31
Entity Filer Category	Accelerated Filer
Entity Common Stock, Shares Outstanding		57,961,673
Entity Well-known Seasoned Issuer	Yes
Entity Public Float			$ 469,318,596
Entity Current Reporting Status	Yes
Entity Voluntary Filers	No