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
	Apr. 30, 2014	Apr. 30, 2013
Earnings Per Share Disclosure [Line Items]
Antidilutive securities excluded from computation of earnings per share, amount	3,372	1,188
Net income (loss) attributable to Mentor Graphics shareholders	$ (2,551)	$ 205
Non-controlling interest adjustment to redemption value	667	468
Net income (loss) attributable to Mentor Graphics shareholders, diluted	$ (1,884)	$ 673
Weighted average common shares used to calculate basic net income (loss) per share (in shares)	114,935	112,711
Employee stock options, restricted stock units and employee stock purchase plan (in shares)	0	3,040
Weighted average common and potential common shares used to calculate diluted net income (loss) per share (in shares)	114,935	115,751
Basic net income (loss) per share attributable to Mentor Graphics shareholders (in dollars per share)	$ (0.02)	$ 0.01
Diluted net income (loss) per share attributable to Mentor Graphics shareholders (in dollars per share)	$ (0.02)	$ 0.01