XML 57 R48.htm IDEA: XBRL DOCUMENT
v3.23.1

Financial Instruments - Schedule of Interest Rate Risk Management Activities (Details) - Cash Flow Hedging - Designated As Hedges: $ in Thousands | Mar. 31, 2023 USD ($)
--- | ---
Forward Interest Rate Swap |
Derivative [Line Items] |
Derivative notional amount | $ 1,500,000
Forward Interest Rate Swap, Planned Issued Fiscal 2024 |
Derivative [Line Items] |
Derivative notional amount | 600,000
Forward Interest Rate Swap, Planned Issued Fiscal 2025 |
Derivative [Line Items] |
Derivative notional amount | 600,000
Forward Interest Rate Swap, Planned Issued Fiscal 2026 |
Derivative [Line Items] |
Derivative notional amount | $ 300,000

X
- Definition Amount of hedged item in hedging relationship. Excludes hedged asset or liability. + References No definition available. + Details
Name: | us-gaap_DerivativeAmountOfHedgedItem
Namespace Prefix: | us-gaap_
Data Type: | xbrli:monetaryItemType
Balance Type: | na
Period Type: | instant

X
- 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_DerivativeLineItems
Namespace Prefix: | us-gaap_
Data Type: | xbrli:stringItemType
Balance Type: | na
Period Type: | duration

X
- Details
Name: | us-gaap_DerivativeInstrumentsGainLossByHedgingRelationshipAxis=us-gaap_CashFlowHedgingMember
Namespace Prefix: |
Data Type: | na
Balance Type: |
Period Type: |

X
- Details
Name: | us-gaap_HedgingDesignationAxis=us-gaap_DesignatedAsHedgingInstrumentMember
Namespace Prefix: |
Data Type: | na
Balance Type: |
Period Type: |

X
- Details
Name: | us-gaap_DerivativeInstrumentRiskAxis=ato_ForwardInterestRateSwapMember
Namespace Prefix: |
Data Type: | na
Balance Type: |
Period Type: |

X
- Details
Name: | us-gaap_DerivativeInstrumentRiskAxis=ato_ForwardInterestRateSwapPlannedIssuedFiscal2024Member
Namespace Prefix: |
Data Type: | na
Balance Type: |
Period Type: |

X
- Details
Name: | us-gaap_DerivativeInstrumentRiskAxis=ato_ForwardInterestRateSwapPlannedIssuedFiscal2025Member
Namespace Prefix: |
Data Type: | na
Balance Type: |
Period Type: |

X
- Details
Name: | us-gaap_DerivativeInstrumentRiskAxis=ato_ForwardInterestRateSwapPlannedIssuedFiscal2026Member
Namespace Prefix: |
Data Type: | na
Balance Type: |
Period Type: |