Segment Information (Details) (USD $) In Millions, unless otherwise specified	3 Months Ended		9 Months Ended
	Sep. 30, 2013	Sep. 30, 2012	Sep. 30, 2013 segment	Sep. 30, 2012
Segment Reporting Information
Number of reportable segments (segment)			3
Percentage of ownership interest in project (as a percent)	75.00%		75.00%
Revenues
Molybdenum sales	$ 85.7	$ 72.6	$ 303.1	$ 291.8
Tolling, calcining and other	5.1	2.3	14.2	10.2
Total revenues	90.8	74.9	317.3	302.0
Cost and expenses
Operating expenses	64.1	85.7	206.4	290.8
Selling and marketing	1.4	1.4	6.4	4.5
Depreciation, depletion and amortization	14.4	17.0	44.7	48.1
Accretion expense	0.6	0.5	2.0	1.6
Total costs and expenses	86.3	112.1	278.5	369.0
Segment revenue less costs and expenses	4.5	(37.2)	38.8	(67.0)
Other segment income
(Gain) loss on foreign exchange	(24.2)	(21.3)	30.0	(20.0)
Segment income				(33.3)
US Operations Molybdenum
Revenues
Molybdenum sales	67.1	53.4	246.2	227.9
Tolling, calcining and other	5.1	2.3	14.2	10.2
Total revenues	72.2	55.7	260.4	238.1
Cost and expenses
Operating expenses	44.8	59.3	150.1	213.4
Selling and marketing	1.8	1.0	5.3	3.2
Depreciation, depletion and amortization	8.2	4.8	24.9	16.0
Accretion expense	0.3	0.4	1.0	1.2
Total costs and expenses	55.1	65.5	181.3	233.8
Segment revenue less costs and expenses	17.1	(9.8)	79.1	4.3
Other segment income
(Gain) loss on foreign exchange	0.1	(1.2)	0.5	(1.1)
Segment income	17.0	(8.6)	78.6	5.4
Canadian Operations Molybdenum
Revenues
Molybdenum sales	19.1	19.7	57.4	65.6
Tolling, calcining and other	0	0	0	0
Total revenues	19.1	19.7	57.4	65.6
Cost and expenses
Operating expenses	19.8	26.9	56.8	79.0
Selling and marketing	(0.1)	0.7	1.9	2.2
Depreciation, depletion and amortization	5.7	11.6	18.4	30.6
Accretion expense	0.2	0.1	0.7	0.3
Total costs and expenses	25.6	39.3	77.8	112.1
Segment revenue less costs and expenses	(6.5)	(19.6)	(20.4)	(46.5)
Other segment income
(Gain) loss on foreign exchange	0.3	(2.1)	0.8	(2.1)
Segment income	(6.8)	(17.5)	(21.2)	(44.4)
Copper-Gold (Development)
Revenues
Molybdenum sales	0	0	0	0
Tolling, calcining and other	0	0	0	0
Total revenues	0		0	0
Cost and expenses
Operating expenses	0	0	0	0
Selling and marketing	0	0	0	0
Depreciation, depletion and amortization	0	0	0	0
Accretion expense	0.1	0	0.3	0.1
Total costs and expenses	0.1		0.3	0.1
Segment revenue less costs and expenses	(0.1)		(0.3)	(0.1)
Other segment income
(Gain) loss on foreign exchange	(4.2)	(6.0)	5.9	(5.0)
Segment income	4.1	6.0	(6.2)	4.9
Operating Segments
Revenues
Molybdenum sales	85.7	72.6	303.1	291.8
Tolling, calcining and other	5.1	2.3	14.2	10.2
Total revenues	90.8	74.9	317.3	302.0
Cost and expenses
Operating expenses	64.1	85.7	206.4	290.8
Selling and marketing	1.4	1.4	6.4	4.5
Depreciation, depletion and amortization	13.9	16.4	43.3	46.6
Accretion expense	0.6	0.5	2.0	1.6
Total costs and expenses	80.0	104.0	258.1	343.5
Segment revenue less costs and expenses	10.8	(29.1)	59.2	(41.5)
Other segment income
(Gain) loss on foreign exchange	(3.8)	(9.3)	7.2	(8.2)
Segment income	14.6	(19.8)	52.0	(33.3)
Inter-segment
Revenues
Molybdenum sales	(0.5)	(0.5)	(0.5)	(1.7)
Tolling, calcining and other	0	0	0	0
Total revenues	(0.5)	(0.5)	(0.5)	(1.7)
Cost and expenses
Operating expenses	(0.5)	(0.5)	(0.5)	(1.6)
Selling and marketing	(0.3)	(0.3)	(0.8)	(0.9)
Depreciation, depletion and amortization	0	0	0	0
Accretion expense	0	0	0	0
Total costs and expenses	(0.8)	(0.8)	(1.3)	(2.5)
Segment revenue less costs and expenses	0.3	0.3	0.8	0.8
Other segment income
(Gain) loss on foreign exchange	0	0	0	0
Segment income	$ 0.3	$ 0.3	$ 0.8	$ 0.8