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, 2015	Apr. 30, 2014
Antidilutive Securities Excluded from Computation of Earnings Per Share [Line Items]
Antidilutive securities excluded from computation of earnings per share, amount	2,638	2,587
Net loss attributable to Mentor Graphics shareholders	$ (9,885)	$ (2,551)
Adjustment to redemption value of non-controlling interest with redemption feature	269	667
Adjusted net loss attributable to Mentor Graphics shareholders	(9,616)	(1,884)
Weighted average common shares used to calculate basic net loss per share	116,003	114,935
Employee stock options, restricted stock units and employee stock purchase plan	0	0
Weighted average common and potential common shares used to calculate diluted net loss per share	116,003	114,935
Basic net loss per share	$ (0.08)	$ (0.02)
Diluted net loss per share	$ (0.08)	$ (0.02)
Convertible Debt Securities [Member]
Antidilutive Securities Excluded from Computation of Earnings Per Share [Line Items]
Antidilutive securities excluded from computation of earnings per share, amount	2,116	548
Interest, net of tax, to be forfeited upon conversion	$ 519	$ 519