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Description of business and significant accounting policies (Narrative) (Details)
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9 Months Ended |
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Sep. 28, 2013
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| Noncontrolling Interest [Line Items] | |
| Year Founded | 1973 |
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Opta Minerals Inc [Member]
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| Noncontrolling Interest [Line Items] | |
| Noncontrolling Interest, Ownership Percentage by Parent | 66.10% |
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Mascoma [Member]
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| Noncontrolling Interest [Line Items] | |
| Cost Method Investments Percentage | 18.70% |