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
	Apr. 30, 2013	Apr. 30, 2012
Disclosure Computation Of Basic And Diluted Net Loss Per Share [Abstract]
Net income attributable to Mentor Graphics shareholders	$ 205	$ 28,182
Non-controlling interest adjustment to redemption value	468	0
Net income (loss) attributable to parent, diluted	$ 673	$ 28,182
Weighted average common shares used to calculate basic net income per share (in shares)	112,711	109,907
Employee stock options, restricted stock units and employee stock purchase plan (in shares)	3,040	3,336
Weighted average common and potential common shares used to calculate diluted net income per share (in shares)	115,751	113,243
Basic net income per share attributable to Mentor Graphics shareholders (in dollars per share)	$ 0.01	$ 0.26
Diluted net income per share attributable to Mentor Graphics shareholders (in dollars per share)	$ 0.01	$ 0.25