Commitments and contingencies (Details) (USD $)	9 Months Ended	147 Months Ended				9 Months Ended		1 Months Ended	45 Months Ended
	Sep. 30, 2013	Sep. 30, 2013	Dec. 31, 2012	Dec. 31, 2011 MW	Apr. 30, 2010	Sep. 30, 2013 Logan Kruger [Member]	Sep. 30, 2013 Grundartangi Power Agreement [Member]	Apr. 30, 2013 CAWV Total Pension Contribution over Agreement [Member]	Dec. 31, 2016 CAWV Total Pension Contribution over Agreement [Member]
Environmental Contingencies [Abstract]
Aggregate environmental-related accrued liabilities	$ 1,322,000	$ 1,322,000	$ 906,000
Environmental Remediation Expense Minimum Amount Entitling Reimbursement by Third Party	400,000
Amount expended on hydrocarbon recovery plan under EPA Administrative Order		985,000
Legal Contingencies [Abstract]
Damages sought for breach of contract and wrongful termination						20,000,000
Legal settlement award payment							1,470,000
PBCG Settlement [Abstract]
Pension Contributions									17,400,000
Pension Expense								5,900,000
OR Power Agreement [Abstract]
Power currently available under the power purchase agreement (in megawatts)				47.5
Power prepayments	$ 2,000,000	$ 2,000,000
Labor Commitments [Abstract]
Percentage of U.S. based work force represented by a union (in hundredths)	75.00%	75.00%
Number of labor unions foreign subsidiary entered into a new labor agreement with					5
Percentage of foreign work force represented by the labor unions (in hundredths)					84.00%