Condensed Consolidated Statements of Equity Condensed Consolidated Statements of Equity - USD ($) shares in Thousands, $ in Thousands	Total	Additional Paid-in Capital	Retained Earnings	Accumulated Other Comprehensive Loss	Total SSI Shareholders’ Equity	Noncontrolling Interests	Class A Common Stock	Class A Common Stock Common Stock	Class B Common Stock	Class B Common Stock Common Stock
Beginning balance (in shares) at Aug. 31, 2017								26,859		200
Beginning balance at Aug. 31, 2017	$ 537,493	$ 38,050	$ 503,770	$ (35,293)	$ 533,586	$ 3,907		$ 26,859		$ 200
Increase (Decrease) in Stockholders' Equity [Roll Forward]
Net income	19,221	0	18,364	0	18,364	857		0		0
Other comprehensive loss, net of tax	(1,627)	0	0	(1,627)	(1,627)	0		0		0
Distributions to noncontrolling interests	(331)	0	0	0	0	(331)		$ 0		$ 0
Issuance of restricted stock (in shares)								241		0
Issuance of restricted stock, value	0	(241)	0	0	0	0		$ 241		$ 0
Restricted stock withheld for taxes (in shares)								(97)		0
Restricted stock withheld for taxes	(2,851)	(2,754)	0	0	(2,851)	0		$ (97)		$ 0
Share-based compensation expense	5,004	5,004	0	0	5,004	0		0		0
Cash dividends	(5,292)	0	(5,292)	0	(5,292)	0		$ 0		$ 0
Ending balance (in shares) at Nov. 30, 2017								27,003		200
Ending balance at Nov. 30, 2017	551,617	40,059	516,842	(36,920)	547,184	4,433		$ 27,003		$ 200
Beginning balance (in shares) at Aug. 31, 2018							26,502	26,502	200	200
Beginning balance at Aug. 31, 2018	670,110	36,929	639,684	(37,237)	666,078	4,032		$ 26,502		$ 200
Increase (Decrease) in Stockholders' Equity [Roll Forward]
Net income	16,618	0	16,188	0	16,188	430		0		0
Other comprehensive loss, net of tax	(1,162)	0	0	(1,162)	(1,162)	0		0		0
Distributions to noncontrolling interests	(393)	0	0	0	0	(393)		$ 0		$ 0
Share repurchase (in shares)								(150)		0
Share repurchase	(4,095)	(3,945)	0	0	(4,095)	0		$ (150)		$ 0
Issuance of restricted stock (in shares)								750		0
Issuance of restricted stock, value	0	(750)	0	0	0	0		$ 750		$ 0
Restricted stock withheld for taxes (in shares)								(276)		0
Restricted stock withheld for taxes	(7,322)	(7,046)	0	0	(7,322)	0		$ (276)		$ 0
Share-based compensation expense	7,404	7,404	0	0	7,404	0		0		0
Cash dividends	(5,177)	0	(5,177)	0	(5,177)	0		$ 0		$ 0
Ending balance (in shares) at Nov. 30, 2018							26,826	26,826	200	200
Ending balance at Nov. 30, 2018	$ 675,983	$ 32,592	$ 650,695	$ (38,399)	$ 671,914	$ 4,069		$ 26,826		$ 200