Document and Entity Information	9 Months Ended
	Oct. 31, 2012	Nov. 30, 2012
Document Type	10-Q
Amendment Flag	false
Document Period End Date	Oct. 31, 2012
Document Fiscal Year Focus	2013
Document Fiscal Period Focus	Q3
Trading Symbol	MENT
Entity Registrant Name	MENTOR GRAPHICS CORP
Entity Central Index Key	0000701811
Current Fiscal Year End Date	--01-31
Entity Filer Category	Large Accelerated Filer
Common Stock, Shares, Outstanding		112,472,570