Quarterly Financial Data (Unaudited) - Schedule of Quarterly Financial Information (Details) - USD ($) $ / shares in Units, $ in Thousands	3 Months Ended								12 Months Ended
	Aug. 31, 2019	May 31, 2019	Feb. 28, 2019	Nov. 30, 2018	Aug. 31, 2018	May 31, 2018	Feb. 28, 2018	Nov. 30, 2017	Aug. 31, 2019		Aug. 31, 2018		Aug. 31, 2017
Quarterly Financial Data [Abstract]
Revenues	$ 547,800	$ 547,396	$ 473,565	$ 564,020	$ 669,577	$ 652,416	$ 559,443	$ 483,279	$ 2,132,781		$ 2,364,715		$ 1,687,591
Cost of goods sold	479,117	474,598	414,688	490,132	582,608	549,164	472,462	406,251	1,858,535		2,010,485		1,464,508
Operating income	17,681	24,459	19,036	22,689	37,973	51,234	33,358	26,423	83,865		148,988		56,013
Income from continuing operations attributable to SSI shareholders	$ 11,621	$ 15,682	$ 13,030	$ 16,260	$ 59,396	$ 37,458	$ 40,852	$ 18,399	$ 56,593		$ 156,105		$ 44,901
Basic income per share from continuing operations attributable to SSI shareholders	$ 0.42	$ 0.57	$ 0.47	$ 0.59	$ 2.17	$ 1.35	$ 1.47	$ 0.66	$ 2.06		$ 5.65		$ 1.63
Diluted income per share from continuing operations attributable to SSI shareholders	$ 0.41	$ 0.56	$ 0.46	$ 0.57	$ 2.08	$ 1.31	$ 1.42	$ 0.64	$ 2.01		$ 5.46		$ 1.60
Net income	$ 11,967	$ 16,440	$ 13,297	$ 16,618	$ 60,201	$ 38,448	$ 41,919	$ 19,221	$ 58,322		$ 159,789		$ 46,978
Net income attributable to SSI shareholders	$ 11,575	$ 15,690	$ 12,892	$ 16,188	$ 59,669	$ 37,402	$ 41,016	$ 18,364	$ 56,345		$ 156,451		$ 44,511
Basic net income per share attributable to SSI shareholders	$ 0.42	$ 0.57	$ 0.47	$ 0.59	$ 2.18	$ 1.35	$ 1.48	$ 0.66	$ 2.05		$ 5.66		$ 1.62
Diluted net income per share attributable to SSI shareholders	$ 0.41	$ 0.56	$ 0.46	$ 0.57	$ 2.09	$ 1.31	$ 1.42	$ 0.64	$ 2.00	[1]	$ 5.47	[1]	$ 1.58	[1]

[1] May not foot due to rounding.