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Balance Type:	na
Period Type:	instant

- Definition

Rate case revenue benchmark as set in the APT rate case filing and part of our regulatory mechanism. This revenue benchmark is used in calculating the total revenue to be billed or returned to customers.

+ References

No definition available.

+ Details

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Namespace Prefix:	ato_
Data Type:	xbrli:monetaryItemType
Balance Type:	credit
Period Type:	duration

- Definition

APT has a regulatory mechanism that requires that we share with its tariffed customers a set percentage, as determined through the rate case filings, of the difference between the total non-tariffed revenues earned during a test period and a revenue benchmark.

+ References

No definition available.

+ Details

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Namespace Prefix:	ato_
Data Type:	dtr-types1:percentItemType
Balance Type:	na
Period Type:	duration

- Definition

Self Insured Retention Deductible

+ References

No definition available.

+ Details

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Namespace Prefix:	ato_
Data Type:	xbrli:monetaryItemType
Balance Type:	credit
Period Type:	duration

- Definition

The aggregate amount of write-downs for impairments recognized during the period for long lived assets held for use (including those held for disposal by means other than sale).

+ References

Reference 1: http://fasb.org/us-gaap/role/ref/legacyRef
-Name Accounting Standards Codification
-Section 45
-Paragraph 28
-Subparagraph (b)
-SubTopic 10
-Topic 230
-Publisher FASB
-URI https://asc.fasb.org/1943274/2147482740/230-10-45-28

Reference 2: http://www.xbrl.org/2003/role/exampleRef
-Topic 820
-SubTopic 10
-Name Accounting Standards Codification
-Section 55
-Paragraph 100
-Subparagraph (c)
-Publisher FASB
-URI https://asc.fasb.org/1943274/2147482078/820-10-55-100

Reference 3: http://fasb.org/us-gaap/role/ref/legacyRef
-Topic 360
-SubTopic 10
-Name Accounting Standards Codification
-Section 50
-Paragraph 2
-Subparagraph (b)
-Publisher FASB
-URI https://asc.fasb.org/1943274/2147482099/360-10-50-2

Reference 4: http://fasb.org/us-gaap/role/ref/legacyRef
-Name Accounting Standards Codification
-Topic 360
-SubTopic 10
-Section 45
-Paragraph 4
-Publisher FASB
-URI https://asc.fasb.org/1943274/2147482130/360-10-45-4

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Data Type:	xbrli:monetaryItemType
Balance Type:	debit
Period Type:	duration

- Definition

Composite depreciation rate for public utility plants in service.

+ References

No definition available.

+ Details

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Namespace Prefix:	us-gaap_
Data Type:	dtr-types:percentItemType
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Namespace Prefix:
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Period Type:

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Summary of Significant Accounting Policies - Narrative (Details)		1 Months Ended	12 Months Ended
	Nov. 30, 2023 USD ($)	Dec. 31, 2023 USD ($)	Sep. 30, 2024 USD ($) plan mi	Sep. 30, 2023 USD ($)	Sep. 30, 2022 USD ($)
Alternative Revenue Program [Line Items]
Number of asset management plans under management \| plan			2
Composite depreciation rate for regulated property, plant and equipment			2.90%	3.00%	3.00%
Impairment of long-lived assets			$ 0	$ 0	$ 0
Derivative, cash collateral			0	$ 0
Self-insured retention			$ 1,000,000
Pipeline and Storage
Alternative Revenue Program [Line Items]
Regulatory mechanism threshold (in percent)			75.00%
Rate case revenue benchmark	$ 69,400,000	$ 106,900,000
Pipeline and Storage \| Louisiana
Alternative Revenue Program [Line Items]
Length of pipeline \| mi			21