v3.26.1

Commitments and Contingencies (Details) $ in Millions	1 Months Ended		3 Months Ended
Commitments and Contingencies (Details) $ in Millions	Aug. 31, 2025 class	Aug. 31, 2024 class	Mar. 31, 2026 USD ($) a	Jun. 30, 2024 organization
Commitments and Contingencies Disclosure [Abstract]
Acres of land \| a			2,200
Renewal options term			35 years
Option to extend			ten years
Percentage of annual lease payment			2.00%
Lease commencement term			3 years
Unconditional purchase obligation \| $			$ 54
Number of regional transmission organizations with show cause proceedings \| organization				4
Number of putative classes \| class	3	3

Annual Lease Payment, Increase, Percentage

+ References

No definition available.

+ Details

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Period Type:	duration

- Definition

Lessee, Operating Lease, Acres Of Land

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No definition available.

+ Details

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Balance Type:	na
Period Type:	instant

- Definition

Lessee, Operating Lease, Lease Commencement Term

+ References

No definition available.

+ Details

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Data Type:	xbrli:durationItemType
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Period Type:	duration

- Definition

Number Of Putative Classes

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No definition available.

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Balance Type:	na
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- Definition

Number Of Regional Transmission Organizations With Show Cause Proceedings

+ References

No definition available.

+ Details

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Namespace Prefix:	ottr_
Data Type:	xbrli:integerItemType
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- References

No definition available.

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- Definition

Description of terms and conditions of option to extend lessee's operating lease that has not yet commenced. Includes, but is not limited to, information about option recognized as part of right-of-use asset and lease liability.

+ References

Reference 1: http://www.xbrl.org/2009/role/commonPracticeRef
-Topic 842
-SubTopic 20
-Name Accounting Standards Codification
-Section 50
-Paragraph 3
-Subparagraph (b)
-Publisher FASB
-URI https://asc.fasb.org/1943274/2147478964/842-20-50-3

+ Details

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

- Definition

Term of lessee's operating lease not yet commenced, in 'PnYnMnDTnHnMnS' format, for example, 'P1Y5M13D' represents reported fact of one year, five months, and thirteen days.

+ References

+ Details

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Data Type:	xbrli:durationItemType
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- Definition

Amount of unrecorded obligation to transfer funds in future for fixed or minimum amount or quantity of product and service at fixed or minimum price. Includes, but is not limited to, lease not yet commenced and take-or-pay and throughput contracts.

+ References

Reference 1: http://www.xbrl.org/2003/role/disclosureRef
-Topic 440
-SubTopic 10
-Name Accounting Standards Codification
-Section 50
-Paragraph 4
-Subparagraph (b)
-Publisher FASB
-URI https://asc.fasb.org/1943274/2147482648/440-10-50-4

Reference 2: http://www.xbrl.org/2009/role/commonPracticeRef
-Topic 842
-SubTopic 20
-Name Accounting Standards Codification
-Section 50
-Paragraph 3
-Subparagraph (b)
-Publisher FASB
-URI https://asc.fasb.org/1943274/2147478964/842-20-50-3

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Balance Type:	credit
Period Type:	instant

Otter Tail Corp 10-Q