Net Income Per Share (Details) - USD ($) $ in Thousands	3 Months Ended		6 Months Ended
	Feb. 28, 2018	Feb. 28, 2017	Feb. 28, 2018	Feb. 28, 2017
Earnings Per Share [Abstract]
Income from continuing operations	$ 41,755	$ 11,794	$ 61,011	$ 11,139
Net income attributable to noncontrolling interests	(903)	(662)	(1,760)	(1,280)
Income from continuing operations attributable to SSI	40,852	11,132	59,251	9,859
Income (loss) from discontinued operations, net of tax	164	(95)	129	(148)
Net income attributable to SSI	$ 41,016	$ 11,037	$ 59,380	$ 9,711
Computation of shares:
Weighted average common shares outstanding, basic (in shares)	27,797,000	27,524,000	27,745,000	27,447,000
Incremental common shares attributable to dilutive performance share awards, DSUs, and RSUs (in shares)	1,008,000	340,000	992,000	367,000
Weighted average common shares outstanding, diluted (in shares)	28,805,000	27,864,000	28,737,000	27,814,000
Antidilutive Securities Excluded from Computation of Earnings Per Share, Amount (in shares)		238,767		220,624