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v3.23.1

Commitments and Contingencies (Details) - Supply Commitment | 6 Months Ended
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Mar. 31, 2023 $ / Mcf MMcf
Long-term Purchase Commitment [Line Items] |
Contract term | 1 year
Purchase commitment volume | 7,300
Weighted Average |
Long-term Purchase Commitment [Line Items] |
Fixed price contracts (USD per Mcf) | $ / Mcf | 2.64
Short-term Contract with Customer |
Long-term Purchase Commitment [Line Items] |
Contract term | 1 year
Purchase commitment volume | 81,200
Long-term Contract with Customer Within Two To Three Years |
Long-term Purchase Commitment [Line Items] |
Purchase commitment volume | 109,200
Long-term Contract with Customer Within Two To Three Years | Minimum |
Long-term Purchase Commitment [Line Items] |
Contract term | 2 years
Long-term Contract with Customer Within Two To Three Years | Maximum |
Long-term Purchase Commitment [Line Items] |
Contract term | 3 years
Long-term Contract with Customer Beyond Three Years |
Long-term Purchase Commitment [Line Items] |
Contract term | 3 years
Purchase commitment volume | 3,100

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- Definition Long Term Purchase Commitment, Per Unit + References No definition available. + Details
Name: | ato_LongTermPurchaseCommitmentPerUnit
Namespace Prefix: | ato_
Data Type: | dtr-types:monetaryPerVolumeItemType
Balance Type: | na
Period Type: | duration

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- Definition Line items represent financial concepts included in a table. These concepts are used to disclose reportable information associated with domain members defined in one or many axes to the table. + References No definition available. + Details
Name: | us-gaap_LongTermPurchaseCommitmentLineItems
Namespace Prefix: | us-gaap_
Data Type: | xbrli:stringItemType
Balance Type: | na
Period Type: | duration

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- Definition Volume that must be purchased within the specified time period of the agreement to avoid penalties or unfavorable effects on pricing, among other adverse consequences. + References No definition available. + Details
Name: | us-gaap_LongTermPurchaseCommitmentMinimumVolumeRequired
Namespace Prefix: | us-gaap_
Data Type: | dtr-types:volumeItemType
Balance Type: | na
Period Type: | duration

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- Definition Period covered by the long-term purchase commitment, in 'PnYnMnDTnHnMnS' format, for example, 'P1Y5M13D' represents the reported fact of one year, five months, and thirteen days. + References No definition available. + Details
Name: | us-gaap_LongtermPurchaseCommitmentPeriod
Namespace Prefix: | us-gaap_
Data Type: | xbrli:durationItemType
Balance Type: | na
Period Type: | duration

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- Details
Name: | us-gaap_SupplyCommitmentAxis=us-gaap_SupplyCommitmentMember
Namespace Prefix: |
Data Type: | na
Balance Type: |
Period Type: |

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- Details
Name: | srt_RangeAxis=srt_WeightedAverageMember
Namespace Prefix: |
Data Type: | na
Balance Type: |
Period Type: |

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- Details
Name: | us-gaap_ContractWithCustomerDurationAxis=us-gaap_ShortTermContractWithCustomerMember
Namespace Prefix: |
Data Type: | na
Balance Type: |
Period Type: |

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- Details
Name: | us-gaap_ContractWithCustomerDurationAxis=ato_LongtermContractwithCustomerWithinTwoToThreeYearsMember
Namespace Prefix: |
Data Type: | na
Balance Type: |
Period Type: |

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- Details
Name: | srt_RangeAxis=srt_MinimumMember
Namespace Prefix: |
Data Type: | na
Balance Type: |
Period Type: |

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- Details
Name: | srt_RangeAxis=srt_MaximumMember
Namespace Prefix: |
Data Type: | na
Balance Type: |
Period Type: |

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- Details
Name: | us-gaap_ContractWithCustomerDurationAxis=ato_LongTermContractWithCustomerBeyondThreeYearsMember
Namespace Prefix: |
Data Type: | na
Balance Type: |
Period Type: |