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v3.21.1

Long Term Debt (Debt Covenants) (Details) | Dec. 31, 2020
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Maximum |
Debt Instrument [Line Items] |
Debt to capital ratio | 0.7
Syndicated credit facilities |
Debt Instrument [Line Items] |
Debt to capital ratio | 0.56

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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
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Period Type: | duration

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- Definition Indebtedness divided by net capital. + References No definition available. + Details
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Data Type: | xbrli:pureItemType
Balance Type: | na
Period Type: | instant

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- Details
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Namespace Prefix: |
Data Type: | na
Balance Type: |
Period Type: |

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- Details
Name: | us-gaap_DebtInstrumentAxis=ema_SyndicatedCreditFacilitiesMember
Namespace Prefix: |
Data Type: | na
Balance Type: |
Period Type: |