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Financial Instruments - Schedule Of Expected Deferred Gains (Losses) Recognition (Details) $ in Thousands | 9 Months Ended
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Jun. 30, 2022 USD ($)
Derivative Instruments and Hedging Activities Disclosure [Abstract] |
Next twelve months | $ (2,976)
Thereafter | (56,506)
Total | $ (59,482)

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- Definition Cash Flow Hedge Gain (Loss) To Be Reclassified After Twelve Months + References No definition available. + Details
Name: | ato_CashFlowHedgeGainLossToBeReclassifiedAfterTwelveMonths
Namespace Prefix: | ato_
Data Type: | xbrli:monetaryItemType
Balance Type: | credit
Period Type: | duration

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- Definition Cash Flow Hedge Gain (Loss) To Be Reclassified, Total + References No definition available. + Details
Name: | ato_CashFlowHedgeGainLossToBeReclassifiedTotal
Namespace Prefix: | ato_
Data Type: | xbrli:monetaryItemType
Balance Type: | credit
Period Type: | duration

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- Definition The estimated net amount of existing gains or losses on cash flow hedges at the reporting date expected to be reclassified to earnings within the next 12 months. + References Reference 1: http://fasb.org/us-gaap/role/ref/legacyRef -Publisher FASB -Name Accounting Standards Codification -Topic 815 -SubTopic 30 -Section 50 -Paragraph 1 -Subparagraph (c) -URI http://asc.fasb.org/extlink&oid=121549185&loc=d3e80748-113994 + Details
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Namespace Prefix: | us-gaap_
Data Type: | xbrli:monetaryItemType
Balance Type: | credit
Period Type: | duration

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