Revenue (Details) - USD ($) $ in Thousands	3 Months Ended
	Nov. 30, 2018	Nov. 30, 2017
Disaggregation of Revenue [Line Items]
Revenues	$ 564,020	$ 483,279
Ferrous
Disaggregation of Revenue [Line Items]
Revenues	316,047
Nonferrous
Disaggregation of Revenue [Line Items]
Revenues	112,942
Steel
Disaggregation of Revenue [Line Items]
Revenues	101,337
Retail and other
Disaggregation of Revenue [Line Items]
Revenues	33,694
Auto and Metals Recycling
Disaggregation of Revenue [Line Items]
Revenues	436,412
Auto and Metals Recycling | Ferrous
Disaggregation of Revenue [Line Items]
Revenues	298,812
Auto and Metals Recycling | Nonferrous
Disaggregation of Revenue [Line Items]
Revenues	104,181
Auto and Metals Recycling | Steel
Disaggregation of Revenue [Line Items]
Revenues	0
Auto and Metals Recycling | Retail and other
Disaggregation of Revenue [Line Items]
Revenues	33,419
Cascade Steel and Scrap
Disaggregation of Revenue [Line Items]
Revenues	130,386
Cascade Steel and Scrap | Ferrous
Disaggregation of Revenue [Line Items]
Revenues	19,743
Cascade Steel and Scrap | Nonferrous
Disaggregation of Revenue [Line Items]
Revenues	9,031
Cascade Steel and Scrap | Steel
Disaggregation of Revenue [Line Items]
Revenues	101,337
Cascade Steel and Scrap | Retail and other
Disaggregation of Revenue [Line Items]
Revenues	275
Intersegment Eliminations
Disaggregation of Revenue [Line Items]
Revenues	(2,778)
Intersegment Eliminations | Ferrous
Disaggregation of Revenue [Line Items]
Revenues	(2,508)
Intersegment Eliminations | Nonferrous
Disaggregation of Revenue [Line Items]
Revenues	(270)
Intersegment Eliminations | Steel
Disaggregation of Revenue [Line Items]
Revenues	0
Intersegment Eliminations | Retail and other
Disaggregation of Revenue [Line Items]
Revenues	0
Foreign
Disaggregation of Revenue [Line Items]
Revenues	291,642
Foreign | Auto and Metals Recycling
Disaggregation of Revenue [Line Items]
Revenues	263,511
Foreign | Cascade Steel and Scrap
Disaggregation of Revenue [Line Items]
Revenues	28,131
Foreign | Intersegment Eliminations
Disaggregation of Revenue [Line Items]
Revenues	0
Domestic
Disaggregation of Revenue [Line Items]
Revenues	272,378
Domestic | Auto and Metals Recycling
Disaggregation of Revenue [Line Items]
Revenues	172,901
Domestic | Cascade Steel and Scrap
Disaggregation of Revenue [Line Items]
Revenues	102,255
Domestic | Intersegment Eliminations
Disaggregation of Revenue [Line Items]
Revenues	$ (2,778)