Segment Information - Segment Operating Income Reconciliation to Consolidated (Details) - USD ($) $ in Thousands	3 Months Ended		6 Months Ended
	Feb. 28, 2019	Feb. 28, 2018	Feb. 28, 2019	Feb. 28, 2018
Segment Reporting Information [Line Items]
Operating income	$ 19,036	$ 33,358	$ 41,725	$ 59,781
Restructuring charges and other exit-related activities	(536)	(91)	(738)	(191)
Interest expense	(2,067)	(2,281)	(3,973)	(4,340)
Other income, net	321	101	344	950
Income from continuing operations before income taxes	17,290	31,178	38,096	56,391
Operating Segments
Segment Reporting Information [Line Items]
Operating income	27,509	50,545	62,444	94,193
Operating Segments | Auto and Metals Recycling
Segment Reporting Information [Line Items]
Operating income	21,741	45,132	44,758	80,304
Operating Segments | Cascade Steel and Scrap
Segment Reporting Information [Line Items]
Operating income	5,768	5,413	17,686	13,889
Segment Reconciling Items
Segment Reporting Information [Line Items]
Restructuring charges and other exit-related activities	(536)	(91)	(738)	(191)
Corporate and eliminations
Segment Reporting Information [Line Items]
Operating income	$ (7,937)	$ (17,096)	$ (19,981)	$ (34,221)