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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% |  |  |  |

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- Definition Total costs accrued as of the balance sheet date for environmental loss contingencies. + References Reference 1: http://www.xbrl.org/2003/role/presentationRef -Publisher FASB -Name Accounting Standards Codification -Topic 410 -SubTopic 30 -Section 50 -Paragraph 7 -URI http://asc.fasb.org/extlink&oid=6393242&loc=d3e13207-110859 Reference 2: http://www.xbrl.org/2003/role/presentationRef -Publisher FASB -Name Accounting Standards Codification -Topic 450 -SubTopic 20 -Section 50 -Paragraph 1 -URI http://asc.fasb.org/extlink&oid=25496072&loc=d3e14326-108349 Reference 3: http://www.xbrl.org/2003/role/presentationRef -Publisher FASB -Name Accounting Standards Codification -Topic 450 -SubTopic 20 -Section 25 -Paragraph 2 -URI http://asc.fasb.org/extlink&oid=6395460&loc=d3e13647-108346 + Details
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