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Commitments and Contingencies (Details) $ in Millions | Mar. 31, 2021 USD ($)
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Otter Tail Power Company | Federal Energy Regulatory Commission |
Other Commitments [Line Items] |
Estimated liability of refund obligation | $ 3.7

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- Definition This element represents amount of estimated liability for FERC ordered MISO tariff ROE refund obligation. + References No definition available. + Details
Name: | ottr_Ottr_EstimatedLiabilityForFERCOrderedMISOTariffRefundObligation
Namespace Prefix: | ottr_
Data Type: | xbrli:monetaryItemType
Balance Type: | credit
Period Type: | instant

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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_OtherCommitmentsLineItems
Namespace Prefix: | us-gaap_
Data Type: | xbrli:stringItemType
Balance Type: | na
Period Type: | duration

X
- Details
Name: | dei_LegalEntityAxis=ottr_OtterTailPowerCompanyMember
Namespace Prefix: |
Data Type: | na
Balance Type: |
Period Type: |

X
- Details
Name: | us-gaap_RegulatoryAgencyAxis=ottr_FederalEnergyRegulatoryCommissionMember
Namespace Prefix: |
Data Type: | na
Balance Type: |
Period Type: |