XML 128 R10.htm IDEA: XBRL DOCUMENT v3.19.3.a.u2

Consolidated Statements of Capitalization (Parentheticals)	12 Months Ended
	Dec. 31, 2019	Dec. 31, 2018
The 3.55% Guaranteed Senior Notes, due December 15, 2026 [Member] | Parent Company [Member]
Long-term Debt, Interest Rate	3.55%	3.55%
Long-term Debt, Due Date	Dec. 15, 2026	Dec. 15, 2026
Partnership in Assisting Community Expansion Note, 2.54%, due March 18, 2021 [Member] | Parent Company [Member]
Long-term Debt, Interest Rate	2.54%	2.54%
Long-term Debt, Due Date	Mar. 18, 2021	Mar. 18, 2021
Senior Unsecured Notes 4.63%, Due December 1, 2021 [Member]
Long-term Debt, Interest Rate	4.63%	4.63%
Long-term Debt, Due Date	Dec. 01, 2021	Dec. 01, 2021
Senior Unsecured Notes 4.63%, Due December 1, 2021 [Member] | Otter Tail Power Company [Member]
Long-term Debt, Interest Rate	4.63%	4.63%
Long-term Debt, Due Date	Dec. 01, 2021	Dec. 01, 2021
Senior Unsecured Notes 6.15%, Series B, Due August 20, 2022 [Member]
Long-term Debt, Interest Rate	6.15%	6.15%
Long-term Debt, Due Date	Aug. 20, 2022	Aug. 20, 2022
Senior Unsecured Notes 6.15%, Series B, Due August 20, 2022 [Member] | Otter Tail Power Company [Member]
Long-term Debt, Interest Rate	6.15%	6.15%
Long-term Debt, Due Date	Aug. 20, 2022	Aug. 20, 2022
Senior Unsecured Notes 6.37%, Series C, Due August 20, 2027 [Member]
Long-term Debt, Interest Rate	6.37%	6.37%
Long-term Debt, Due Date	Aug. 20, 2027	Aug. 20, 2027
Senior Unsecured Notes 6.37%, Series C, Due August 20, 2027 [Member] | Otter Tail Power Company [Member]
Long-term Debt, Interest Rate	6.37%	6.37%
Long-term Debt, Due Date	Aug. 20, 2027	Aug. 20, 2027
Senior Unsecured Notes 4.68%, Series A, Due February 27, 2029 [Member]
Long-term Debt, Interest Rate	4.68%	4.68%
Long-term Debt, Due Date	Feb. 27, 2029	Feb. 27, 2029
Senior Unsecured Notes 4.68%, Series A, Due February 27, 2029 [Member] | Otter Tail Power Company [Member]
Long-term Debt, Interest Rate	4.68%	4.68%
Long-term Debt, Due Date	Feb. 27, 2029	Feb. 27, 2029
Senior Unsecured notes 3.07%, Series 2019A, Due October 10, 2029 [Member] | Otter Tail Power Company [Member]
Long-term Debt, Interest Rate	3.07%
Long-term Debt, Due Date	Oct. 10, 2029
Senior Unsecured Notes 6.47%, Series D, Due August 20, 2037 [Member]
Long-term Debt, Interest Rate	6.47%	6.47%
Long-term Debt, Due Date	Aug. 20, 2037	Aug. 20, 2037
Senior Unsecured Notes 6.47%, Series D, Due August 20, 2037 [Member] | Otter Tail Power Company [Member]
Long-term Debt, Interest Rate	6.47%	6.47%
Long-term Debt, Due Date	Aug. 20, 2037	Aug. 20, 2037
Senior Unsecured Notes 3.52%, Series 2019B, Due October 10, 2039 [Member]
Long-term Debt, Interest Rate	3.52%
Long-term Debt, Due Date	Oct. 10, 2039
Senior Unsecured Notes 3.52%, Series 2019B, Due October 10, 2039 [Member] | Otter Tail Power Company [Member]
Long-term Debt, Interest Rate	3.52%
Long-term Debt, Due Date	Oct. 10, 2039
Senior Unsecured Notes 5.47%, Series B, Due February 27, 2044 [Member]
Long-term Debt, Interest Rate	5.47%	5.47%
Long-term Debt, Due Date	Feb. 27, 2044	Feb. 27, 2044
Senior Unsecured Notes 5.47%, Series B, Due February 27, 2044 [Member] | Otter Tail Power Company [Member]
Long-term Debt, Interest Rate	5.47%	5.47%
Long-term Debt, Due Date	Feb. 27, 2044	Feb. 27, 2044
Senior Unsecured Notes 4.07%, Series 2018A, Due February 7, 2048 [Member]
Long-term Debt, Interest Rate	4.07%	4.07%
Long-term Debt, Due Date	Feb. 07, 2048	Feb. 07, 2048
Senior Unsecured Notes 4.07%, Series 2018A, Due February 7, 2048 [Member] | Otter Tail Power Company [Member]
Long-term Debt, Interest Rate	4.07%	4.07%
Long-term Debt, Due Date	Feb. 07, 2048	Feb. 07, 2048
Senior Unsecured Notes 3.82%, Sericies C, Due October 10, 2049 [Member]
Long-term Debt, Interest Rate	3.82%
Long-term Debt, Due Date	Oct. 10, 2049
Senior Unsecured Notes 3.82%, Sericies C, Due October 10, 2049 [Member] | Otter Tail Power Company [Member]
Long-term Debt, Interest Rate	3.82%
Long-term Debt, Due Date	Oct. 10, 2049

X

- Definition

Contractual interest rate for funds borrowed, under the debt agreement.

+ References

Reference 1: http://fasb.org/us-gaap/role/ref/legacyRef
-Publisher FASB
-Name Accounting Standards Codification
-Topic 210
-SubTopic 10
-Section S99
-Paragraph 1
-Subparagraph (SX 210.5-02.22(a)(1))
-URI http://asc.fasb.org/extlink&oid=6877327&loc=d3e13212-122682

+ Details

Name:	us-gaap_DebtInstrumentInterestRateStatedPercentage
Namespace Prefix:	us-gaap_
Data Type:	num:percentItemType
Balance Type:	na
Period Type:	instant

X

- Definition

Date when the debt instrument is scheduled to be fully repaid, in CCYY-MM-DD format.

+ References

Reference 1: http://www.xbrl.org/2003/role/disclosureRef
-Publisher FASB
-Name Accounting Standards Codification
-Topic 210
-SubTopic 10
-Section S99
-Paragraph 1
-Subparagraph (SX 210.5-02.22(a)(2))
-URI http://asc.fasb.org/extlink&oid=6877327&loc=d3e13212-122682

Reference 2: http://www.xbrl.org/2009/role/commonPracticeRef
-Publisher FASB
-Name Accounting Standards Codification
-Topic 820
-SubTopic 10
-Section 50
-Paragraph 2
-Subparagraph (bbb)(2)
-URI http://asc.fasb.org/extlink&oid=117815213&loc=d3e19207-110258

+ Details

Name:	us-gaap_DebtInstrumentMaturityDate
Namespace Prefix:	us-gaap_
Data Type:	xbrli:dateItemType
Balance Type:	na
Period Type:	duration

X

- Details

Name:	us-gaap_DebtInstrumentAxis=ottr_The3Point55PercentGuaranteedSeniorNotesDueDecember152026Member
Namespace Prefix:
Data Type:	na
Balance Type:
Period Type:

X

- Details

Name:	srt_ConsolidatedEntitiesAxis=srt_ParentCompanyMember
Namespace Prefix:
Data Type:	na
Balance Type:
Period Type:

X

- Details

Name:	us-gaap_DebtInstrumentAxis=ottr_PartnershipInAssistingCommunityExpansionNote2Point54PercentDueMarch182021Member
Namespace Prefix:
Data Type:	na
Balance Type:
Period Type:

X

- Details

Name:	us-gaap_DebtInstrumentAxis=ottr_SeniorUnsecuredNotes463DueDecember12021Member
Namespace Prefix:
Data Type:	na
Balance Type:
Period Type:

X

- Details

Name:	srt_ConsolidatedEntitiesAxis=ottr_OtterTailPowerCompanyMember
Namespace Prefix:
Data Type:	na
Balance Type:
Period Type:

X

- Details

Name:	us-gaap_DebtInstrumentAxis=ottr_SeniorUnsecuredNotes615SeriesBDueAugust202022Member
Namespace Prefix:
Data Type:	na
Balance Type:
Period Type:

X

- Details

Name:	us-gaap_DebtInstrumentAxis=ottr_SeniorUnsecuredNotes637SeriesCDueAugust202027Member
Namespace Prefix:
Data Type:	na
Balance Type:
Period Type:

X

- Details

Name:	us-gaap_DebtInstrumentAxis=ottr_SeniorUnsecuredNotes468SeriesADueFebruary272029Member
Namespace Prefix:
Data Type:	na
Balance Type:
Period Type:

X

- Details

Name:	us-gaap_DebtInstrumentAxis=ottr_SeniorUnsecuredNotes307Series2019aDueOctober102029Member
Namespace Prefix:
Data Type:	na
Balance Type:
Period Type:

X

- Details

Name:	us-gaap_DebtInstrumentAxis=ottr_SeniorUnsecuredNotes647SeriesDDueAugust202037Member
Namespace Prefix:
Data Type:	na
Balance Type:
Period Type:

X

- Details

Name:	us-gaap_DebtInstrumentAxis=ottr_SeniorUnsecuredNotes352Series2019bDueOctober102039Member
Namespace Prefix:
Data Type:	na
Balance Type:
Period Type:

X

- Details

Name:	us-gaap_DebtInstrumentAxis=ottr_SeniorUnsecuredNotes547SeriesBDueFebruary272044Member
Namespace Prefix:
Data Type:	na
Balance Type:
Period Type:

X

- Details

Name:	us-gaap_DebtInstrumentAxis=ottr_SeniorUnsecuredNotes407Series2018ADueFebruary72048Member
Namespace Prefix:
Data Type:	na
Balance Type:
Period Type:

X

- Details

Name:	us-gaap_DebtInstrumentAxis=ottr_SeniorUnsecuredNotes382SericiesCDueOctober102049Member
Namespace Prefix:
Data Type:	na
Balance Type:
Period Type: