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

X

- 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

X

- 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: