Segment Information (Details) (USD $) In Millions, unless otherwise specified	3 Months Ended		6 Months Ended
	Jun. 30, 2013	Jun. 30, 2012	Jun. 30, 2013 segment	Jun. 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	$ 112.7	$ 109.6	$ 217.4	$ 219.2
Tolling, calcining and other	5.1	3.9	9.1	7.9
Total revenues	117.8	113.5	226.5	227.1
Cost and expenses
Operating expenses	73.8	110.6	142.4	210.2
Selling and marketing	2.7	2.2	5.0	4.1
Depreciation, depletion and amortization	17.5	11.5	30.3	31.1
Accretion expense	0.6	0.6	1.4	1.1
Total costs and expenses	100.6	131.9	192.3	262.0
Segment revenue less costs and expenses	17.2	(18.4)	34.2	(34.9)
Other segment income
Loss on foreign exchange	(34.8)	(7.9)	(54.2)	(1.3)
Segment income (loss) before income and mining taxes				(19.6)
US Operations Molybdenum
Revenues
Molybdenum sales	89.3	90.0	179.1	174.5
Tolling, calcining and other	5.1	3.9	9.1	7.9
Total revenues	94.4	93.9	188.2	182.4
Cost and expenses
Operating expenses	51.9	83.2	105.3	154.1
Selling and marketing	1.8	1.2	3.5	3.2
Depreciation, depletion and amortization	9.2	5.5	16.7	11.2
Accretion expense	0.4	0.4	0.7	0.8
Total costs and expenses	63.3	90.3	126.2	169.3
Segment revenue less costs and expenses	31.1	3.6	62.0	13.1
Other segment income
Loss on foreign exchange	(0.3)	0.7	0.4	0.1
Segment income (loss) before income and mining taxes	31.4	2.9	61.6	13.0
Canadian Operations Molybdenum
Revenues
Molybdenum sales	23.4	20.8	38.3	45.9
Tolling, calcining and other	0	0	0	0
Total revenues	23.4	20.8	38.3	45.9
Cost and expenses
Operating expenses	21.9	28.5	37.1	57.2
Selling and marketing	1.2	1.3	2.0	1.5
Depreciation, depletion and amortization	7.9	5.7	12.7	19.0
Accretion expense	0.1	0.1	0.5	0.2
Total costs and expenses	31.1	35.6	52.3	77.9
Segment revenue less costs and expenses	(7.7)	(14.8)	(14.0)	(32.0)
Other segment income
Loss on foreign exchange	(1.1)	0.9	0.5	0
Segment income (loss) before income and mining taxes	(6.6)	(15.7)	(14.5)	(32.0)
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	0.1	0.2	0.1
Total costs and expenses	0.1	0.1	0.2	0.1
Segment revenue less costs and expenses	(0.1)	(0.1)	(0.2)	(0.1)
Other segment income
Loss on foreign exchange	6.3	4.0	10.1	1.0
Segment income (loss) before income and mining taxes	(6.4)	(4.1)	(10.3)	(1.1)
Operating Segments
Revenues
Molybdenum sales	112.7	109.6	217.4	219.2
Tolling, calcining and other	5.1	3.9	9.1	7.9
Total revenues	117.8	113.5	226.5	227.1
Cost and expenses
Operating expenses	73.8	110.6	142.4	210.2
Selling and marketing	2.7	2.2	5.0	4.1
Depreciation, depletion and amortization	17.1	11.2	29.4	30.2
Accretion expense	0.6	0.6	1.4	1.1
Total costs and expenses	94.2	124.6	178.2	245.6
Segment revenue less costs and expenses	23.6	(11.1)	48.3	(18.5)
Other segment income
Loss on foreign exchange	4.9	5.6	11.0	1.1
Segment income (loss) before income and mining taxes	18.7	(16.7)	37.3	(19.6)
Inter-segment
Revenues
Molybdenum sales		(1.2)	0	(1.2)
Tolling, calcining and other	0	0	0	0
Total revenues	0	(1.2)	0	(1.2)
Cost and expenses
Operating expenses	0	(1.1)	0	(1.1)
Selling and marketing	(0.3)	(0.3)	(0.5)	(0.6)
Depreciation, depletion and amortization	0	0	0	0
Accretion expense	0	0	0	0
Total costs and expenses	(0.3)	(1.4)	(0.5)	(1.7)
Segment revenue less costs and expenses	0.3	0.2	0.5	0.5
Other segment income
Loss on foreign exchange	0	0	0	0
Segment income (loss) before income and mining taxes	$ 0.3	$ 0.2	$ 0.5	$ 0.5