Document and Entity Information (USD $)	12 Months Ended
	Jan. 31, 2015	Mar. 12, 2015	Jul. 31, 2014
Entity Information
Entity Registrant Name	MENTOR GRAPHICS CORP
Entity Central Index Key	0000701811
Trading Symbol	MENT
Current Fiscal Year End Date	--01-31
Entity Filer Category	Large Accelerated Filer
Document Type	10-K
Document Period End Date	Jan. 31, 2015
Document Fiscal Year Focus	2015
Document Fiscal Period Focus	FY
Amendment Flag	false
Entity Common Stock, Shares Outstanding		116,083,159
Entity Well-known Seasoned Issuer	Yes
Entity Voluntary Filers	No
Entity Current Reporting Status	Yes
Entity Public Float			$ 2,239,709,229