Quarterly Financial Data (unaudited) (Details) (USD $) In Thousands, except Per Share data, unless otherwise specified	3 Months Ended								12 Months Ended
	Dec. 31, 2013	Sep. 30, 2013	Jun. 30, 2013	Mar. 31, 2013	Dec. 31, 2012	Sep. 30, 2012	Jun. 30, 2012	Mar. 31, 2012	Dec. 31, 2013	Dec. 31, 2012	Dec. 31, 2011
Revenue from External Customer [Line Items]
Net sales	$ 256,600	$ 254,200	$ 256,800	$ 250,400	$ 243,100	$ 247,800	$ 251,400	$ 254,500	$ 1,018,181	$ 996,764	$ 1,032,933
Gross profit	59,000	59,900	58,800	56,000	54,300	55,600	56,800	55,600	233,645	222,298	214,190
Income from operations	33,500	32,800	32,400	28,200	27,000	28,600	30,100	27,900	126,852	113,640	104,059
Income from continuing operations	23,600	22,600	22,700	20,300	19,100	19,700	20,700	19,200	86,074	76,597	70,053
Loss from discontinued operations	0	0	(5,000)	(700)	(900)	(500)	(500)	(600)	(5,744)	(2,450)	(2,532)
Net income attributable to MTI	22,600	21,900	17,100	18,700	17,700	18,600	19,700	18,000	80,330	74,147	67,521
Basic EPS [Abstract]
Income from continuing operations attributable to MTI (in dollars per share)	$ 0.66	$ 0.63	$ 0.63	$ 0.56	$ 0.53	$ 0.54	$ 0.57	$ 0.53	$ 2.48	$ 2.17	$ 1.94
Loss from discontinued operations attributable to MTI (in dollars per share)	$ 0	$ 0	$ (0.14)	$ (0.02)	$ (0.03)	$ (0.01)	$ (0.01)	$ (0.02)	$ (0.17)	$ (0.07)	$ (0.07)
Net Income attributable to MTI common shareholders (in dollars per share)	$ 0.66	$ 0.63	$ 0.49	$ 0.54	$ 0.50	$ 0.53	$ 0.56	$ 0.51	$ 2.31	$ 2.10	$ 1.87
Diluted EPS [Abstract]
Income from continuing operations attributable to MTI (in dollars per share)	$ 0.65	$ 0.63	$ 0.63	$ 0.55	$ 0.53	$ 0.54	$ 0.57	$ 0.53	$ 2.46	$ 2.16	$ 1.93
Loss from discontinued operations attributable to MTI (in dollars per share)	$ 0	$ 0	$ (0.14)	$ (0.02)	$ (0.03)	$ (0.01)	$ (0.01)	$ (0.02)	$ (0.16)	$ (0.07)	$ (0.07)
Net Income attributable to MTI common shareholders (in dollars per share)	$ 0.65	$ 0.63	$ 0.49	$ 0.53	$ 0.50	$ 0.53	$ 0.56	$ 0.51	$ 2.30	$ 2.09	$ 1.86
Market price range per share of common stock [Abstract]
High (in dollars per share)	$ 60.40	$ 49.03	$ 43.12	$ 43.04	$ 39.92	$ 36.99	$ 33.60	$ 33.96
Low (in dollars per share)	$ 49.28	$ 42.53	$ 38.43	$ 39.54	$ 34.25	$ 30.50	$ 30.81	$ 28.78
Close (in dollars per share)	$ 60.07	$ 48.95	$ 41.34	$ 41.51	$ 39.92	$ 35.46	$ 31.89	$ 32.70	$ 60.07	$ 39.92
Dividends paid per common share (in dollars per share)	$ 0.05	$ 0.05	$ 0.05	$ 0.05	$ 0.05	$ 0.025	$ 0.025	$ 0.025	$ 0.20
PCC [Member]
Revenue from External Customer [Line Items]
Net sales	138,300	135,900	135,600	137,200	133,700	134,500	133,700	135,500
Processed Minerals [Member]
Revenue from External Customer [Line Items]
Net sales	28,800	31,500	32,700	29,600	26,000	28,600	31,800	29,600
Specialty Minerals [Member]
Revenue from External Customer [Line Items]
Net sales	167,100	167,400	168,300	166,800	159,700	163,100	165,500	165,100	669,800	653,400	664,100
Refractories [Member]
Revenue from External Customer [Line Items]
Net sales	$ 89,500	$ 86,800	$ 88,500	$ 83,600	$ 83,400	$ 84,700	$ 85,900	$ 89,400	$ 348,400	$ 343,400	$ 368,800