Net Income Per Share (Details) (USD $) In Thousands, except Share data, unless otherwise specified	3 Months Ended		6 Months Ended
	Feb. 29, 2012	Feb. 28, 2011	Feb. 29, 2012	Feb. 28, 2011
Earnings Per Share Basic And Diluted By Common Class [Line Items]
Income from continuing operations	$ 10,365	$ 32,123	$ 18,107	$ 51,017
Net income attributable to noncontrolling interests	(735)	(1,309)	(1,462)	(2,432)
Income from continuing operations attributable to SSI	9,630	30,814	16,645	48,585
Income (loss) from discontinued operations, net of tax	0	11	0	34
Net income attributable to SSI	$ 9,630	$ 30,825	$ 16,645	$ 48,619
Computation of shares:
Weighted average common shares outstanding, basic	27,509,000	27,627,000	27,480,000	27,595,000
Incremental common shares attributable to dilutive stock options, performance share awards, DSUs and RSUs	272,000	317,000	254,000	323,000
Weighted average common shares outstanding, diluted	27,781,000	27,944,000	27,734,000	27,918,000
Antidilutive Securities Excluded from Computation of Earnings Per Share, Amount	57,364	27,194	92,107	48,678