Revenue - Summary of Revenues Disaggregated by Major Product and Sales Destination for Each Reportable Segment (Details) - USD ($) $ in Thousands	3 Months Ended		9 Months Ended
	May 31, 2020	May 31, 2019	May 31, 2020	May 31, 2019
Disaggregation of Revenue [Line Items]
Revenues	$ 402,683	$ 547,396	$ 1,247,749	$ 1,584,981
Ferrous Revenues
Disaggregation of Revenue [Line Items]
Revenues	201,972	291,873	633,936	869,887
Nonferrous Revenues
Disaggregation of Revenue [Line Items]
Revenues	85,506	122,832	277,869	344,116
Steel Revenues
Disaggregation of Revenue [Line Items]
Revenues	83,414	96,626	246,278	271,988
Retail and Other Revenues
Disaggregation of Revenue [Line Items]
Revenues	31,791	36,065	89,666	98,990
Operating Segments | AMR
Disaggregation of Revenue [Line Items]
Revenues	300,377	429,023	950,803	1,251,500
Operating Segments | CSS
Disaggregation of Revenue [Line Items]
Revenues	104,550	121,431	302,975	342,215
Operating Segments | Ferrous Revenues | AMR
Disaggregation of Revenue [Line Items]
Revenues	189,783	280,362	604,720	836,662
Operating Segments | Ferrous Revenues | CSS
Disaggregation of Revenue [Line Items]
Revenues	14,115	14,208	34,486	41,071
Operating Segments | Nonferrous Revenues | AMR
Disaggregation of Revenue [Line Items]
Revenues	78,858	112,785	256,571	316,450
Operating Segments | Nonferrous Revenues | CSS
Disaggregation of Revenue [Line Items]
Revenues	6,966	10,376	22,057	28,522
Operating Segments | Steel Revenues | AMR
Disaggregation of Revenue [Line Items]
Revenues	0	0	0	0
Operating Segments | Steel Revenues | CSS
Disaggregation of Revenue [Line Items]
Revenues	83,414	96,626	246,278	271,988
Operating Segments | Retail and Other Revenues | AMR
Disaggregation of Revenue [Line Items]
Revenues	31,736	35,876	89,512	98,388
Operating Segments | Retail and Other Revenues | CSS
Disaggregation of Revenue [Line Items]
Revenues	55	221	154	634
Intersegment Revenue Eliminations
Disaggregation of Revenue [Line Items]
Revenues	(2,244)	(3,058)	(6,029)	(8,734)
Intersegment Revenue Eliminations | Ferrous Revenues
Disaggregation of Revenue [Line Items]
Revenues	(1,926)	(2,697)	(5,270)	(7,846)
Intersegment Revenue Eliminations | Nonferrous Revenues
Disaggregation of Revenue [Line Items]
Revenues	(318)	(329)	(759)	(856)
Intersegment Revenue Eliminations | Steel Revenues
Disaggregation of Revenue [Line Items]
Revenues	0	0	0	0
Intersegment Revenue Eliminations | Retail and Other Revenues
Disaggregation of Revenue [Line Items]
Revenues	0	(32)	0	(32)
Foreign
Disaggregation of Revenue [Line Items]
Revenues	213,403	298,370	656,388	823,092
Foreign | Operating Segments | AMR
Disaggregation of Revenue [Line Items]
Revenues	188,203	273,128	589,110	753,696
Foreign | Operating Segments | CSS
Disaggregation of Revenue [Line Items]
Revenues	25,200	25,242	67,278	69,396
Foreign | Intersegment Revenue Eliminations
Disaggregation of Revenue [Line Items]
Revenues	0	0	0	0
Domestic
Disaggregation of Revenue [Line Items]
Revenues	189,280	249,026	591,361	761,889
Domestic | Operating Segments | AMR
Disaggregation of Revenue [Line Items]
Revenues	112,174	155,895	361,693	497,804
Domestic | Operating Segments | CSS
Disaggregation of Revenue [Line Items]
Revenues	79,350	96,189	235,697	272,819
Domestic | Intersegment Revenue Eliminations
Disaggregation of Revenue [Line Items]
Revenues	$ (2,244)	$ (3,058)	$ (6,029)	$ (8,734)