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		9 Months Ended
	Oct. 31, 2013	Oct. 31, 2012	Oct. 31, 2013	Oct. 31, 2012
Earnings Per Share Disclosure [Line Items]
Antidilutive securities excluded from computation of earnings per share, amount	73	1,205	1,238	2,626
Net income attributable to Mentor Graphics shareholders	$ 25,535	$ 30,641	$ 49,722	$ 76,990
Non-controlling interest adjustment to redemption value	(2,032)	0	(3,913)	0
Net income (loss) attributable to parent, diluted	$ 23,503	$ 30,641	$ 45,809	$ 76,990
Weighted average common shares used to calculate basic net income per share (in shares)	113,986	111,575	113,232	110,454
Employee stock options, restricted stock units and employee stock purchase plan (in shares)	3,092	3,146	3,163	3,130
Weighted average common and potential common shares used to calculate diluted net income per share (in shares)	117,078	114,721	116,395	113,584
Basic net income per share attributable to Mentor Graphics shareholders (in dollars per share)	$ 0.21	$ 0.27	$ 0.40	$ 0.70
Diluted net income per share attributable to Mentor Graphics shareholders (in dollars per share)	$ 0.20	$ 0.27	$ 0.39	$ 0.68