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Employee Postretirement Benefits - Composition of Periodic Benefit Cost (Details) - USD ($) $ in Thousands	3 Months Ended
	Mar. 31, 2023	Mar. 31, 2022
Retirement Benefits [Abstract]
Net Periodic Benefit Cost (Income)	$ (1,724)	$ 1,479
Net Amount Amortized (Deferred) Due to the Effect of Regulation	408	527
Net Periodic Benefit Cost (Income) Recognized	$ (1,316)	$ 2,006

X

- Definition

Defined Benefit Plan, Net Periodic Benefit Cost (Credit), Deferred

+ References

No definition available.

+ Details

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X

- Definition

Defined Benefit Plan, Net Periodic Benefit Cost (Credit), Net of Deferrals

+ References

No definition available.

+ Details

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Namespace Prefix:	ottr_
Data Type:	xbrli:monetaryItemType
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Period Type:	duration

X

- References

No definition available.

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X

- Definition

Amount of net periodic benefit cost (credit) for defined benefit plan.

+ References

Reference 1: http://www.xbrl.org/2003/role/disclosureRef
-Publisher FASB
-Name Accounting Standards Codification
-Topic 715
-SubTopic 20
-Section 50
-Paragraph 6
-Subparagraph (a)
-URI https://asc.fasb.org/extlink&oid=123447040&loc=d3e2709-114920

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-Publisher FASB
-Name Accounting Standards Codification
-Topic 715
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-Section 55
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-URI https://asc.fasb.org/extlink&oid=123450688&loc=d3e4179-114921

Reference 3: http://www.xbrl.org/2003/role/exampleRef
-Publisher FASB
-Name Accounting Standards Codification
-Topic 715
-SubTopic 20
-Section 55
-Paragraph 18
-URI https://asc.fasb.org/extlink&oid=123450688&loc=d3e4587-114921

Reference 4: http://www.xbrl.org/2003/role/disclosureRef
-Publisher FASB
-Name Accounting Standards Codification
-Topic 715
-SubTopic 20
-Section 50
-Paragraph 1
-Subparagraph (h)
-URI https://asc.fasb.org/extlink&oid=123447040&loc=d3e1928-114920

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