Net Income Per Share - Computation of Basic and Diluted Net Income Per Share (Details) (USD $) In Thousands, except Per Share data, unless otherwise specified	3 Months Ended								12 Months Ended
	Jan. 31, 2015	Oct. 31, 2014	Jul. 31, 2014	Apr. 30, 2014	Jan. 31, 2014	Oct. 31, 2013	Jul. 31, 2013	Apr. 30, 2013	Jan. 31, 2015	Jan. 31, 2014	Jan. 31, 2013
Disclosure Computation Of Basic And Diluted Net Loss Per Share [Abstract]
Net income attributable to Mentor Graphics shareholders	$ 114,488	$ 21,030	$ 14,172	$ (2,551)	$ 105,536	$ 25,535	$ 23,982	$ 205	$ 147,139	$ 155,258	$ 138,736
Adjustment to redemption value of non-controlling interest with redemption feature	(1,174)	(267)	895	667	(573)	(2,032)	(2,349)	468	121	(4,486)	(5,272)
Adjusted net income attributable to Mentor Graphics shareholders									$ 147,260	$ 150,772	$ 133,464
Weighted average common shares used to calculate basic net income per share									114,635	113,671	110,998
Employee stock options, restricted stock units and employee stock purchase plan									2,443	3,031	3,019
Weighted average common and potential common shares used to calculate diluted net income per share									117,078	116,702	114,017
Basic net income per share attributable to Mentor Graphics shareholders (in dollars per share)	$ 0.98	$ 0.18	$ 0.13	$ (0.02)	$ 0.91	$ 0.21	$ 0.19	$ 0.01	$ 1.28	$ 1.33	$ 1.20
Diluted net income per share attributable to Mentor graphics shareholders (in dollars per share)	$ 0.96	$ 0.18	$ 0.13	$ (0.02)	$ 0.89	$ 0.20	$ 0.19	$ 0.01	$ 1.26	$ 1.29	$ 1.17