Net Income Per Share (Details) - USD ($) $ in Thousands	3 Months Ended		9 Months Ended
	May 31, 2018	May 31, 2017	May 31, 2018	May 31, 2017
Earnings Per Share [Abstract]
Income from continuing operations	$ 38,504	$ 17,379	$ 99,515	$ 28,518
Net income attributable to noncontrolling interests	(1,046)	(687)	(2,806)	(1,967)
Income from continuing operations attributable to SSI	37,458	16,692	96,709	26,551
Income (loss) from discontinued operations, net of tax	(56)	(127)	72	(275)
Net income attributable to SSI	$ 37,402	$ 16,565	$ 96,781	$ 26,276
Computation of shares:
Weighted average common shares outstanding, basic (in shares)	27,676,000	27,601,000	27,719,000	27,499,000
Incremental common shares attributable to dilutive performance share awards, DSUs, and RSUs (in shares)	960,000	102,000	927,000	193,000
Weighted average common shares outstanding, diluted (in shares)	28,636,000	27,703,000	28,646,000	27,692,000
Antidilutive Securities Excluded from Computation of Earnings Per Share, Amount (in shares)	0	375,653	0	309,476