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								12 Months Ended
	Jan. 31, 2014	Oct. 31, 2013	Jul. 31, 2013	Apr. 30, 2013	Jan. 31, 2013	Oct. 31, 2012	Jul. 31, 2012	Apr. 30, 2012	Jan. 31, 2014	Jan. 31, 2013	Jan. 31, 2012
Disclosure Computation Of Basic And Diluted Net Loss Per Share [Abstract]
Net income attributable to Mentor Graphics shareholders	$ 105,536	$ 25,535	$ 23,982	$ 205	$ 61,746	$ 30,641	$ 18,167	$ 28,182	$ 155,258	$ 138,736	$ 83,872
Non-controlling interest adjustment to redemption value	(573)	(2,032)	(2,349)	468	(5,272)	0	0	0	(4,486)	(5,272)	0
Net income (loss) net of adjustments to redemption value									$ 150,772	$ 133,464	$ 83,872
Weighted average common shares used to calculate basic net income per share (in shares)									113,671	110,998	110,138
Employee stock options, restricted stock units and employee stock purchase plan (in shares)									3,031	3,019	2,777
Weighted average common and potential common shares used to calculate diluted net income per share (in shares)									116,702	114,017	112,915
Basic net income per share attributable to Mentor Graphics shareholders (in dollars per share)	$ 0.91	$ 0.21	$ 0.19	$ 0.01	$ 0.50	$ 0.27	$ 0.17	$ 0.26	$ 1.33	$ 1.20	$ 0.76
Diluted net income per share attributable to Mentor graphics shareholders (in dollars per share)	$ 0.89	$ 0.20	$ 0.19	$ 0.01	$ 0.49	$ 0.27	$ 0.16	$ 0.25	$ 1.29	$ 1.17	$ 0.74