Quarterly Financial Information - Unaudited (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
Quarterly Financial Information Disclosure [Abstract]
Total revenues	$ 439,066	$ 292,683	$ 260,233	$ 252,151	$ 401,000	$ 275,642	$ 253,216	$ 226,515	$ 1,244,133	$ 1,156,373	$ 1,088,727
Gross profit	388,666	245,142	211,304	194,708	345,003	229,570	208,359	186,334	1,039,820	969,266	899,037
Operating Income	139,532	29,723	16,912	1,644	117,197	33,372	26,578	5,893	187,811	183,040	161,633
Net income (loss) 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
Basic (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 (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
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)