Document and Entity Information (USD $)	12 Months Ended
	Jan. 31, 2013	Mar. 13, 2013	Jul. 31, 2012
Document Type	10-K
Amendment Flag	false
Document Period End Date	Jan. 31, 2013
Document Fiscal Year Focus	2013
Document Fiscal Period Focus	FY
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
Entity Common Stock, Shares Outstanding		112,770,129
Entity Well-known Seasoned Issuer	Yes
Entity Voluntary Filers	No
Entity Current Reporting Status	Yes
Entity Public Float			$ 1,684,791,793