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INVENTORIES - Narrative (Details) - USD ($) $ in Thousands | 12 Months Ended
--- | ---
Dec. 31, 2017 | Dec. 31, 2016 | Dec. 31, 2015
Inventory [Line Items] |  |  |
Impairment loss | $ 3,310 | $ 5,360 | $ 0

X
- Definition Impairment Loss Related to Concentrations and Work-in-Progress Inventory + References No definition available. + Details
Name: | efr_ImpairmentLossRelatedtoConcentrationsandWorkinProgressInventory
Namespace Prefix: | efr_
Data Type: | xbrli:monetaryItemType
Balance Type: | debit
Period Type: | duration

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- Definition Line items represent financial concepts included in a table. These concepts are used to disclose reportable information associated with domain members defined in one or many axes to the table. + References No definition available. + Details
Name: | us-gaap_InventoryLineItems
Namespace Prefix: | us-gaap_
Data Type: | xbrli:stringItemType
Balance Type: | na
Period Type: | duration