Fair Value Of Financial Instruments (Narrative) (Details) (USD $) In Millions, unless otherwise specified	Feb. 29, 2012	Aug. 31, 2011
Fair Value Of Financial Instruments [Abstract]
Senior secured fixed rate notes, carrying value	$ 489.5	$ 497.0

Aggregate carrying amount of long-term fixed rate notes as of the balance sheet date, including current and noncurrent portions as well as accrued interest.

No definition available.

Name:	sonc_LongTermDebtFixedRateNotesAtCarryingValue
Namespace Prefix:	sonc_
Data Type:	xbrli:monetaryItemType
Balance Type:	credit
Period Type:	instant