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		6 Months Ended
	Jul. 31, 2014	Jul. 31, 2013	Jul. 31, 2014	Jul. 31, 2013
Earnings Per Share Disclosure [Line Items]
Antidilutive securities excluded from computation of earnings per share, amount	20	531	701	674
Net income attributable to Mentor Graphics shareholders	$ 14,172	$ 23,982	$ 11,621	$ 24,187
Non-controlling interest adjustment to redemption value	895	(2,349)	1,562	(1,881)
Net income (loss) attributable to Mentor Graphics shareholders, diluted	$ 15,067	$ 21,633	$ 13,183	$ 22,306
Weighted average common shares used to calculate basic net income (loss) per share (in shares)	113,868	112,988	114,396	112,851
Employee stock options, restricted stock units and employee stock purchase plan (in shares)	2,683	3,307	2,564	3,163
Weighted average common and potential common shares used to calculate diluted net income (loss) per share (in shares)	116,551	116,295	116,960	116,014
Basic net income (loss) per share attributable to Mentor Graphics shareholders (in dollars per share)	$ 0.13	$ 0.19	$ 0.12	$ 0.20
Diluted net income (loss) per share attributable to Mentor Graphics shareholders (in dollars per share)	$ 0.13	$ 0.19	$ 0.11	$ 0.19