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Basis of Presentation (Details) | 12 Months Ended
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Dec. 31, 2016 Segment Production_Facility
Organization, Consolidation and Presentation of Financial Statements [Abstract] |
Number of production facilities operated | Production_Facility | 5
Number of reportable segments | Segment | 1

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- Definition Number of Production Facilities Operated + References No definition available. + Details
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Namespace Prefix: | cmt_
Data Type: | xbrli:integerItemType
Balance Type: | na
Period Type: | instant

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- Definition Number of segments reported by the entity. A reportable segment is a component of an entity for which there is an accounting requirement to report separate financial information on that component in the entity's financial statements. + References No definition available. + Details
Name: | us-gaap_NumberOfReportableSegments
Namespace Prefix: | us-gaap_
Data Type: | xbrli:integerItemType
Balance Type: | na
Period Type: | duration

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- References No definition available. + Details
Name: | us-gaap_OrganizationConsolidationAndPresentationOfFinancialStatementsAbstract
Namespace Prefix: | us-gaap_
Data Type: | xbrli:stringItemType
Balance Type: | na
Period Type: | duration