Net Income Per Share - Computation of Basic and Diluted Net Income Per Share (Detail) - USD ($) $ / shares in Units, shares in Thousands, $ in Thousands	3 Months Ended
	Apr. 30, 2016	Apr. 30, 2015
Disclosure Computation Of Basic And Diluted Net Income Per Share [Abstract]
Net loss attributable to Mentor Graphics shareholders	$ (13,436)	$ (9,885)
Adjustment to redemption value of noncontrolling interest with redemption feature	0	269
Adjusted net loss attributable to Mentor Graphics shareholders	$ (13,436)	$ (9,616)
Weighted average common shares used to calculate basic net loss per share	109,085	116,003
Potential common shares	0	0
Weighted average common and potential common shares used to calculate diluted net loss per share	109,085	116,003
Basic net loss per share	$ (0.12)	$ (0.08)
Diluted net loss per share	$ (0.12)	$ (0.08)
Antidilutive Securities Excluded from Computation of Earnings Per Share [Line Items]
Interest, net of tax, to be forfeited upon conversion	$ 0	$ 519
Antidilutive securities excluded from computation of earnings per share, amount	3,557	4,754
Restricted Stock Units (RSUs) [Member]
Antidilutive Securities Excluded from Computation of Earnings Per Share [Line Items]
Antidilutive securities excluded from computation of earnings per share, amount	2,298	1,254
Employee Stock Option [Member]
Antidilutive Securities Excluded from Computation of Earnings Per Share [Line Items]
Antidilutive securities excluded from computation of earnings per share, amount	1,208	1,284
ESPP Purchase Right [Member]
Antidilutive Securities Excluded from Computation of Earnings Per Share [Line Items]
Antidilutive securities excluded from computation of earnings per share, amount	51	100
Convertible Debt [Member]
Antidilutive Securities Excluded from Computation of Earnings Per Share [Line Items]
Antidilutive securities excluded from computation of earnings per share, amount	0	2,116