Segment Information Segment Operating Income Reconciliation to Consolidated (Details) - USD ($) $ in Thousands	3 Months Ended		9 Months Ended
	May 31, 2018	May 31, 2017	May 31, 2018	May 31, 2017
Segment Reporting Information [Line Items]
Operating income	$ 51,234	$ 19,147	$ 111,015	$ 33,905
Restructuring charges and other exit-related activities	(70)	(93)	(261)	200
Interest expense	(2,483)	(2,131)	(6,823)	(5,969)
Other income, net	403	524	1,353	1,318
Income from continuing operations before income taxes	49,154	17,540	105,545	29,254
Operating Segments
Segment Reporting Information [Line Items]
Operating income	65,773	30,683	159,966	64,670
Operating Segments | Auto and Metals Recycling
Segment Reporting Information [Line Items]
Operating income	54,980	29,520	135,284	67,414
Operating Segments | Cascade Steel and Scrap
Segment Reporting Information [Line Items]
Operating income	10,793	1,163	24,682	(2,744)
Segment Reconciling Items
Segment Reporting Information [Line Items]
Restructuring charges and other exit-related activities	(70)	(93)	(261)	200
Corporate and eliminations
Segment Reporting Information [Line Items]
Operating income	$ (14,469)	$ (11,443)	$ (48,690)	$ (30,965)