Segment Information (Details) (USD $) In Millions, unless otherwise specified	3 Months Ended
	Mar. 31, 2013 segment	Mar. 31, 2012
Segment Reporting Information
Number of reportable segments (segment)	3
Percentage of ownership interest in project (as a percent)	75.00%
Revenues
Molybdenum sales	$ 104.7	$ 109.6
Tolling, calcining and other	4.0	4.0
Total revenues	108.7	113.6
Cost and expenses
Operating expenses	68.6	99.6
Selling and marketing	2.3	1.9
Depreciation, depletion and amortization	12.8	19.6
Accretion expense	0.8	0.5
Total costs and expenses	91.7	130.1
Segment revenue less costs and expenses	17.0	(16.5)
Other segment income
Loss (gain) on foreign exchange	19.4	(6.6)
US Operations Molybdenum
Revenues
Molybdenum sales	89.8	84.5
Tolling, calcining and other	4.0	4.0
Total revenues	93.8	88.5
Cost and expenses
Operating expenses	53.4	70.9
Selling and marketing	1.7	1.4
Depreciation, depletion and amortization	7.5	5.7
Accretion expense	0.3	0.4
Total costs and expenses	62.9	78.4
Segment revenue less costs and expenses	30.9	10.1
Other segment income
Loss (gain) on foreign exchange	0.7	(0.6)
Segment income (loss) before income and mining taxes	30.2	10.7
Canadian Operations Molybdenum
Revenues
Molybdenum sales	14.9	25.1
Tolling, calcining and other	0	0
Total revenues	14.9	25.1
Cost and expenses
Operating expenses	15.2	28.7
Selling and marketing	0.8	0.8
Depreciation, depletion and amortization	4.8	13.3
Accretion expense	0.4	0.1
Total costs and expenses	21.2	42.9
Segment revenue less costs and expenses	(6.3)	(17.8)
Other segment income
Loss (gain) on foreign exchange	1.6	(0.9)
Segment income (loss) before income and mining taxes	(7.9)	(16.9)
Copper-Gold (Development)
Revenues
Molybdenum sales	0	0
Tolling, calcining and other	0	0
Total revenues	0	0
Cost and expenses
Operating expenses	0	0
Selling and marketing	0	0
Depreciation, depletion and amortization	0	0
Accretion expense	0.1	0
Total costs and expenses	0.1
Segment revenue less costs and expenses	(0.1)
Other segment income
Loss (gain) on foreign exchange	3.8	(3.0)
Segment income (loss) before income and mining taxes	(3.9)	3.0
Inter-segment
Revenues
Molybdenum sales		0
Tolling, calcining and other	0	0
Total revenues	0	0
Cost and expenses
Operating expenses	0	0
Selling and marketing	(0.2)	(0.3)
Depreciation, depletion and amortization	0	0
Accretion expense	0	0
Total costs and expenses	(0.2)	(0.3)
Segment revenue less costs and expenses	0.2	0.3
Other segment income
Loss (gain) on foreign exchange	0	0
Segment income (loss) before income and mining taxes	0.2	0.3
Total
Revenues
Molybdenum sales	104.7	109.6
Tolling, calcining and other	4.0	4.0
Total revenues	108.7	113.6
Cost and expenses
Operating expenses	68.6	99.6
Selling and marketing	2.3	1.9
Depreciation, depletion and amortization	12.3	19.0
Accretion expense	0.8	0.5
Total costs and expenses	84.0	121.0
Segment revenue less costs and expenses	24.7	(7.4)
Other segment income
Loss (gain) on foreign exchange	6.1	(4.5)
Segment income (loss) before income and mining taxes	$ 18.6	$ (2.9)