Document and Entity Information
In Millions, unless otherwise specified
9 Months Ended
Aug. 31, 2013
Sep. 30, 2013
Document And Entity Information [Abstract]    
Document Type 10-Q  
Amendment Flag false  
Document Period End Date Aug. 31, 2013  
Document Fiscal Year Focus 2013  
Document Fiscal Period Focus Q3  
Trading Symbol GY  
Entity Registrant Name GENCORP INC  
Entity Central Index Key 0000040888  
Current Fiscal Year End Date --11-30  
Entity Filer Category Accelerated Filer  
Entity Common Stock, Shares Outstanding   60.9