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, 2014		May 31, 2014		Feb. 28, 2014		Nov. 30, 2013		Aug. 31, 2013		May 31, 2013		Feb. 28, 2013		Nov. 30, 2012		Aug. 31, 2014		Aug. 31, 2013		Aug. 31, 2012
Earnings Per Share [Abstract]
Net income	$ 18,825	[1],[2]	$ 16,776	[1],[2]	$ 4,107	[1],[2]	$ 8,208	[1],[2]	$ 12,198	[1],[2]	$ 14,793	[1],[2]	$ 3,577	[1],[2]	$ 6,133	[1],[2]	$ 47,916		$ 36,701		$ 36,085
Weighted average common shares outstanding - basic																	55,164		56,384		60,078
Effect of dilutive employee stock options and unvested restricted stock units																	1,455		807		94
Weighted average common shares - diluted																	56,619		57,191		60,172
Net income per common share - basic	$ 0.35	[3]	$ 0.31	[3]	$ 0.07	[3]	$ 0.15	[3]	$ 0.22	[3]	$ 0.26	[3]	$ 0.06	[3]	$ 0.11	[3]	$ 0.87		$ 0.65		$ 0.60
Net income per common share - diluted	$ 0.34	[3]	$ 0.30	[3]	$ 0.07	[3]	$ 0.14	[3]	$ 0.21	[3]	$ 0.26	[3]	$ 0.06	[3]	$ 0.11	[3]	$ 0.85		$ 0.64		$ 0.60
Anti-dilutive securities excluded																	988	[4]	3,278	[4]	6,705	[4]

[1] Includes a $0.5 million tax benefit resulting from the IRS’ acceptance of a federal tax method change during the first quarter of fiscal year 2014.

[2] 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. Also includes 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.

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

[4] 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.