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Summary of Significant Accounting Policies - Inventories (Details) - USD ($) $ in Thousands | 12 Months Ended
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Dec. 31, 2020 | Dec. 31, 2019
Accounting Policies [Abstract] |  |
Provision for slow-moving and obsolete inventories | $ (600) | $ (600)
Reduction of gross inventory levels | $ (1,200) | $ 1,900

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- Definition Increase (Decrease) In Inventory Levels, Gross + References No definition available. + Details
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- Definition Increase (Decrease) In Inventory Reserves + References No definition available. + Details
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Namespace Prefix: | efoi_
Data Type: | xbrli:monetaryItemType
Balance Type: | credit
Period Type: | duration

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- References No definition available. + Details
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Namespace Prefix: | us-gaap_
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