Selected Quarterly Financial Data (Schedule Of Selected Quarterly Financial Data) (Details) (USD $)	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
Total revenues	$ 163,769,000		$ 152,187,000		$ 109,741,000		$ 126,652,000		$ 158,802,000		$ 146,634,000		$ 111,141,000		$ 126,008,000		$ 552,349,000	$ 542,585,000	$ 543,730,000
Income from operations	36,288,000		31,681,000		12,349,000		18,359,000		30,033,000		29,994,000		12,018,000		17,203,000		98,677,000	89,248,000	88,940,000
Net income	18,825,000	[1],[2]	16,776,000	[1],[2]	4,107,000	[1],[2]	8,208,000	[1],[2]	12,198,000	[1],[2]	14,793,000	[1],[2]	3,577,000	[1],[2]	6,133,000	[1],[2]	47,916,000	36,701,000	36,085,000
Basic income per share	$ 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
Diluted income per share	$ 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
Net loss from early extinguishment of debt									3,900,000				500,000					4,443,000
Tax benefits							500,000						700,000
Impairment charge related to write-off of assets									1,600,000
Provision for impairment of long-lived assets																	114,000	1,776,000	764,000
2013 Company Drive-In Closures Member
Loss on closure of Company Drive-Ins									$ 2,400,000									$ 2,400,000
Number of Restaurants									12									12

[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.