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v2.4.0.8

Geographical and Segment Information - Additional Information (Detail) | 12 Months Ended
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Dec. 31, 2013 Facility
Segment Reporting Information [Line Items] |
Number of mines newly acquired | 2

X
- Definition The number of businesses acquired by the entity during the period. + References No definition available. + Details
Name: | us-gaap_NumberOfBusinessesAcquired
Namespace Prefix: | us-gaap_
Data Type: | xbrli:integerItemType
Balance Type: | na
Period Type: | duration

X
- Details
Name: | us-gaap_SegmentReportingInformationLineItems
Namespace Prefix: | us-gaap_
Data Type: | xbrli:stringItemType
Balance Type: | na
Period Type: | duration