Document and Entity Information
In Millions, unless otherwise specified
3 Months Ended
Feb. 28, 2015
Mar. 31, 2015
Document And Entity Information [Abstract]    
Document Type 10-Q  
Amendment Flag false  
Document Period End Date Feb. 28, 2015  
Document Fiscal Year Focus 2015  
Document Fiscal Period Focus Q1  
Trading Symbol GY  
Entity Registrant Name GENCORP INC  
Entity Central Index Key 0000040888  
Current Fiscal Year End Date --11-30  
Entity Filer Category Large Accelerated Filer  
Entity Common Stock, Shares Outstanding   62.6