Net Income Per Share - Computation of Basic and Diluted Net Income Per Share (Detail) (USD $) In Thousands, except Per Share data, unless otherwise specified	3 Months Ended		6 Months Ended
	Jul. 31, 2013	Jul. 31, 2012	Jul. 31, 2013	Jul. 31, 2012
Earnings Per Share Disclosure [Line Items]
Antidilutive securities excluded from computation of earnings per share, amount	531	1,946	674	1,959
Net income attributable to Mentor Graphics shareholders	$ 23,982	$ 18,167	$ 24,187	$ 46,349
Non-controlling interest adjustment to redemption value	(2,349)	0	(1,881)	0
Net income (loss) attributable to parent, diluted	$ 21,633	$ 18,167	$ 22,306	$ 46,349
Weighted average common shares used to calculate basic net income per share (in shares)	112,988	109,875	112,851	109,891
Employee stock options, restricted stock units and employee stock purchase plan (in shares)	3,307	3,171	3,163	3,187
Weighted average common and potential common shares used to calculate diluted net income per share (in shares)	116,295	113,046	116,014	113,078
Basic net income per share attributable to Mentor Graphics shareholders (in dollars per share)	$ 0.19	$ 0.17	$ 0.20	$ 0.42
Diluted net income per share attributable to Mentor Graphics shareholders (in dollars per share)	$ 0.19	$ 0.16	$ 0.19	$ 0.41