v3.8.0.1
Document and Entity Information - USD ($)
12 Months Ended
Aug. 31, 2017
Oct. 20, 2017
Feb. 28, 2017
Entity Information [Line Items]      
Entity Registrant Name SCHNITZER STEEL INDUSTRIES INC    
Entity Central Index Key 0000912603    
Current Fiscal Year End Date --08-31    
Entity Filer Category Accelerated Filer    
Document Type 10-K    
Document Period End Date Aug. 31, 2017    
Document Fiscal Year Focus 2017    
Document Fiscal Period Focus FY    
Amendment Flag false    
Entity Well-known Seasoned Issuer Yes    
Entity Voluntary Filers No    
Entity Current Reporting Status Yes    
Entity Public Float     $ 623,145,280
Class A Common Stock      
Entity Information [Line Items]      
Entity Common Stock, Shares Outstanding   26,862,569  
Class B Common Stock      
Entity Information [Line Items]      
Entity Common Stock, Shares Outstanding   200,000