Earnings Per Share (Computation Of Basic And Diluted Earnings Per Share) (Details) (USD $) In Thousands, except Per Share data, unless otherwise specified	3 Months Ended																12 Months Ended
	Aug. 31, 2013		May 31, 2013		Feb. 28, 2013		Nov. 30, 2012		Aug. 31, 2012		May 31, 2012		Feb. 29, 2012		Nov. 30, 2011		Aug. 31, 2013		Aug. 31, 2012		Aug. 31, 2011
Earnings Per Share [Abstract]
Net income	$ 12,198	[1]	$ 14,793	[1]	$ 3,577	[1]	$ 6,133	[1]	$ 14,502	[1]	$ 14,407	[1]	$ 1,677	[1]	$ 5,499	[1]	$ 36,701		$ 36,085		$ 19,225
Weighted average common shares outstanding - basic																	56,384		60,078		61,781
Effect of dilutive employee stock options and unvested restricted stock units																	807		94		162
Weighted average common shares - diluted																	57,191		60,172		61,943
Net income per common share - basic	$ 0.22	[2]	$ 0.26	[2]	$ 0.06	[2]	$ 0.11	[2]	$ 0.25	[2]	$ 0.24	[2]	$ 0.03	[2]	$ 0.09	[2]	$ 0.65		$ 0.60		$ 0.31
Net income per common share - diluted	$ 0.21	[2]	$ 0.26	[2]	$ 0.06	[2]	$ 0.11	[2]	$ 0.25	[2]	$ 0.24	[2]	$ 0.03	[2]	$ 0.09	[2]	$ 0.64		$ 0.60		$ 0.31
Anti-dilutive securities excluded																	3,278	[3]	6,705	[3]	6,367	[3]

[1] Includes losses on early extinguishment of debt of $0.5 million and $3.9 million in the second and fourth quarter of fiscal year 2013, respectively, a tax benefit of $0.7 million from the retroactive reinstatement of the Work Opportunity Tax Credit (“WOTC”) and resolution of income tax matters in the second quarter of fiscal year 2013, as well as a $2.4 million loss on the closure of 12 lower-performing Company Drive-Ins as a result of an assessment in advance of capital expenditures for pending technology initiatives and an impairment charge of $1.6 million related to the write-off of assets associated with a change in the vendor for the Sonic system’s new point-of-sale technology in the fourth quarter of fiscal year 2013.

[2] The sum of per share data may not agree to annual amounts due to rounding.

[3] Anti-dilutive securities consist of stock options and unvested restricted stock units that were not included in the computation of diluted earnings per share because either the exercise price of the options was greater than the average market price of the common stock or the total assumed proceeds under the treasury stock method resulted in negative incremental shares and thus the inclusion would have been anti-dilutive.