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

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- 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

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- References No definition available. + Details
Name: | us-gaap_IncomeTaxDisclosureAbstract
Namespace Prefix: | us-gaap_
Data Type: | xbrli:stringItemType
Balance Type: | na
Period Type: | duration

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- 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