XML 114 R81.htm IDEA: XBRL DOCUMENT v3.24.0.1

Employee Postretirement Benefits - Summary of Asset Allocation Ranges By Asset Class and PBO Funded Status (Details) - Pension Benefits (Pension Plan)	Dec. 31, 2023	Dec. 31, 2022
Defined Benefit Plan Disclosure [Line Items]
Actual Allocation	100.00%	100.00%
Return Enhancement
Defined Benefit Plan Disclosure [Line Items]
Actual Allocation	48.00%	48.00%
Return Enhancement | 35 - 60% | Minimum
Defined Benefit Plan Disclosure [Line Items]
Permitted Range	35.00%
Return Enhancement | 35 - 60% | Maximum
Defined Benefit Plan Disclosure [Line Items]
Permitted Range	60.00%
Risk Management
Defined Benefit Plan Disclosure [Line Items]
Actual Allocation	51.00%	51.00%
Risk Management | 40 - 80% | Minimum
Defined Benefit Plan Disclosure [Line Items]
Permitted Range	40.00%
Risk Management | 40 - 80% | Maximum
Defined Benefit Plan Disclosure [Line Items]
Permitted Range	80.00%
Alternatives
Defined Benefit Plan Disclosure [Line Items]
Actual Allocation	1.00%	1.00%
Alternatives | 0 - 20% | Minimum
Defined Benefit Plan Disclosure [Line Items]
Permitted Range	0.00%
Alternatives | 0 - 20% | Maximum
Defined Benefit Plan Disclosure [Line Items]
Permitted Range	20.00%

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

X

- Definition

Percentage of target investment allocation to total plan assets. Includes, but is not limited to, percentage on weighted-average basis if more than one plan.

+ References

Reference 1: http://www.xbrl.org/2003/role/exampleRef
-Topic 715
-SubTopic 20
-Name Accounting Standards Codification
-Section 55
-Paragraph 17
-Publisher FASB
-URI https://asc.fasb.org//1943274/2147480482/715-20-55-17

Reference 2: http://www.xbrl.org/2003/role/disclosureRef
-Topic 715
-SubTopic 20
-Name Accounting Standards Codification
-Section 50
-Paragraph 1
-Subparagraph (d)(i)
-Publisher FASB
-URI https://asc.fasb.org//1943274/2147480506/715-20-50-1

+ Details

Name:	us-gaap_DefinedBenefitPlanPlanAssetsTargetAllocationPercentage
Namespace Prefix:	us-gaap_
Data Type:	dtr-types:percentItemType
Balance Type:	na
Period Type:	instant

X

- Definition

Percentage of actual investment allocation to total plan assets. Includes, but is not limited to, percentage on weighted-average basis if more than one plan.

+ References

Reference 1: http://www.xbrl.org/2009/role/commonPracticeRef
-Topic 715
-SubTopic 20
-Name Accounting Standards Codification
-Section 50
-Paragraph 1
-Subparagraph (d)(i)
-Publisher FASB
-URI https://asc.fasb.org//1943274/2147480506/715-20-50-1

+ Details

Name:	us-gaap_DefinedBenefitPlanWeightedAverageAssetAllocations
Namespace Prefix:	us-gaap_
Data Type:	dtr-types:percentItemType
Balance Type:	na
Period Type:	instant

X

- Details

Name:	us-gaap_RetirementPlanTypeAxis=us-gaap_PensionPlansDefinedBenefitMember
Namespace Prefix:
Data Type:	na
Balance Type:
Period Type:

X

- Details

Name:	us-gaap_DefinedBenefitPlanByPlanAssetCategoriesAxis=ottr_DefinedBenefitPlanReturnEnhancementMember
Namespace Prefix:
Data Type:	na
Balance Type:
Period Type:

X

- Details

Name:	us-gaap_RetirementPlanFundingStatusAxis=ottr_PermittedRange35To60PercentMember
Namespace Prefix:
Data Type:	na
Balance Type:
Period Type:

X

- Details

Name:	srt_RangeAxis=srt_MinimumMember
Namespace Prefix:
Data Type:	na
Balance Type:
Period Type:

X

- Details

Name:	srt_RangeAxis=srt_MaximumMember
Namespace Prefix:
Data Type:	na
Balance Type:
Period Type:

X

- Details

Name:	us-gaap_DefinedBenefitPlanByPlanAssetCategoriesAxis=ottr_DefinedBenefitPlanRiskManagementMember
Namespace Prefix:
Data Type:	na
Balance Type:
Period Type:

X

- Details

Name:	us-gaap_RetirementPlanFundingStatusAxis=ottr_PermittedRange40To80PercentMember
Namespace Prefix:
Data Type:	na
Balance Type:
Period Type:

X

- Details

Name:	us-gaap_DefinedBenefitPlanByPlanAssetCategoriesAxis=ottr_DefinedBenefitPlanAlternativesMember
Namespace Prefix:
Data Type:	na
Balance Type:
Period Type:

X

- Details

Name:	us-gaap_RetirementPlanFundingStatusAxis=ottr_PermittedRange0To20PercentMember
Namespace Prefix:
Data Type:	na
Balance Type:
Period Type: