Summary of Significant Accounting Policies (Details 4) (USD $)	12 Months Ended
	Dec. 31, 2013	Dec. 31, 2012	Dec. 31, 2011
Property, plant and equipment
Capitalized interest costs	$ 1,700,000	$ 7,700,000	$ 5,400,000
Present values of the asset retirement obligations	116,393,000	89,478,000	74,963,000
Sustained price decrease over and above prices used in analysis through life of assets that would result in potential impairment as per sensitivity analysis (as a percent)	5.00%
Asset impairment charges		1,107,512,000
Goodwill impairment		1,064,409,000
North River Mine
Property, plant and equipment
Long-lived asset impairments	0
Asset impairment charges	$ 8,000,000
Machinery and equipment | Minimum
Property, plant and equipment
Estimated useful lives	3 years
Machinery and equipment | Maximum
Property, plant and equipment
Estimated useful lives	10 years
Land improvements and building | Minimum
Property, plant and equipment
Estimated useful lives	15 years
Land improvements and building | Maximum
Property, plant and equipment
Estimated useful lives	30 years
Capitalized computer systems and software implementation costs | Minimum
Property, plant and equipment
Estimated useful lives	3 years
Capitalized computer systems and software implementation costs | Maximum
Property, plant and equipment
Estimated useful lives	5 years