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Commitments and Contingencies - Strategic Alliance Agreement - Additional Information (Detail) | 1 Months Ended
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Nov. 30, 2016
Strategic Alliance Agreement [Member] |
Commitments And Contingencies [Line Items] |
Initial term of agreement | 7 years

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- Definition Commitments and contingencies. + References No definition available. + Details
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Namespace Prefix: | watt_
Data Type: | xbrli:stringItemType
Balance Type: | na
Period Type: | duration

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- Definition Initial term of agreement. + References No definition available. + Details
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Namespace Prefix: | watt_
Data Type: | xbrli:durationItemType
Balance Type: | na
Period Type: | duration

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- Details
Name: | us-gaap_TypeOfArrangementAxis=watt_StrategicAllianceAgreementMember
Namespace Prefix: |
Data Type: | na
Balance Type: |
Period Type: |