XML 59 R108.htm IDEA: XBRL DOCUMENT v3.19.3.a.u2

Note 15 - Asset Retirement Obligations (AROs) (Details Textual) $ in Thousands	12 Months Ended
	Dec. 31, 2019 USD ($)	Dec. 31, 2018 USD ($)
Asset Retirement Obligation, Liabilities Incurred	$ 0	$ 0
Otter Tail Power Company [Member]
Asset Retirement Obligation, Liabilities Incurred	$ 0
North Dakota 1 [Member]
Number of Wind Turbines	92

X

- Definition

Represents the number of wind turbines as of a specified date.

+ References

No definition available.

+ Details

Name:	ottr_NumberOfWindTurbines
Namespace Prefix:	ottr_
Data Type:	xbrli:integerItemType
Balance Type:	na
Period Type:	instant

X

- Definition

Amount of asset retirement obligations incurred during the period.

+ References

Reference 1: http://fasb.org/us-gaap/role/ref/legacyRef
-Publisher FASB
-Name Accounting Standards Codification
-Topic 410
-SubTopic 20
-Section 50
-Paragraph 1
-Subparagraph (c)(1)
-URI http://asc.fasb.org/extlink&oid=6392692&loc=d3e7535-110849

+ Details

Name:	us-gaap_AssetRetirementObligationLiabilitiesIncurred
Namespace Prefix:	us-gaap_
Data Type:	xbrli:monetaryItemType
Balance Type:	credit
Period Type:	duration

X

- Details

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

X

- Details

Name:	srt_StatementGeographicalAxis=ottr_NorthDakota1Member
Namespace Prefix:
Data Type:	na
Balance Type:
Period Type: