Net Income (Loss) Per Share - Computation of Basic and Diluted Net Income (Loss) Per Share (Detail) (USD $) In Thousands, except Per Share data, unless otherwise specified	3 Months Ended		9 Months Ended
	Oct. 31, 2014	Oct. 31, 2013	Oct. 31, 2014	Oct. 31, 2013
Earnings Per Share Disclosure [Line Items]
Antidilutive securities excluded from computation of earnings per share, amount	1,677	73	1,189	1,238
Net income attributable to Mentor Graphics shareholders	$ 21,030	$ 25,535	$ 32,651	$ 49,722
Non-controlling interest adjustment to redemption value	(267)	(2,032)	1,295	(3,913)
Net income (loss) attributable to Mentor Graphics shareholders, diluted	$ 20,763	$ 23,503	$ 33,946	$ 45,809
Weighted average common shares used to calculate basic net income (loss) per share (in shares)	114,405	113,986	114,399	113,232
Employee stock options, restricted stock units and employee stock purchase plan (in shares)	2,310	3,092	2,529	3,163
Weighted average common and potential common shares used to calculate diluted net income (loss) per share (in shares)	116,715	117,078	116,928	116,395
Basic net income (loss) per share attributable to Mentor Graphics shareholders (in dollars per share)	$ 0.18	$ 0.21	$ 0.30	$ 0.40
Diluted net income (loss) per share attributable to Mentor Graphics shareholders (in dollars per share)	$ 0.18	$ 0.20	$ 0.29	$ 0.39