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Income Taxes - Narrative (Details) $ in Millions	12 Months Ended
	Dec. 31, 2021 USD ($)
Income Tax Disclosure [Abstract]
Decrease in valuation allowance	$ 0.8
Period for unrecognized tax benefits not expected change	12 months

X

- Definition

Represents the period over which there is no significant expected change in the unrecognized tax benefits.

+ References

No definition available.

+ Details

Name:	ottr_PeriodForUnrecognizedTaxBenefitsNotExpectedChange
Namespace Prefix:	ottr_
Data Type:	xbrli:durationItemType
Balance Type:	na
Period Type:	duration

X

- References

No definition available.

+ Details

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

X

- Definition

Amount of increase (decrease) in the valuation allowance for a specified deferred tax asset.

+ References

Reference 1: http://www.xbrl.org/2003/role/disclosureRef
-Publisher FASB
-Name Accounting Standards Codification
-Topic 740
-SubTopic 10
-Section 50
-Paragraph 2
-URI http://asc.fasb.org/extlink&oid=121826272&loc=d3e32537-109319

+ Details

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