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v3.20.2

Note 1 - Summary of Significant Accounting Policies - Supplemental Disclosure of Cash Flow Information (Details) - USD ($) $ in Thousands | Sep. 30, 2020 | Sep. 30, 2019
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Transactions Related to Capital Additions not Settled in Cash | $ 112,314 | $ 15,893

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- Definition Represents the accounts payable outstanding related to capital additions as part of noncash Investing Activities + References No definition available. + Details
Name: | ottr_AccountsPayableOutstandingRelatedToCapitalAdditions
Namespace Prefix: | ottr_
Data Type: | xbrli:monetaryItemType
Balance Type: | credit
Period Type: | instant