XML 43 R32.htm IDEA: XBRL DOCUMENT
v3.8.0.1

Nature of Business (Details) customers in Millions | Mar. 31, 2018 state customers regulated_gas_distributions_divisions
--- | ---
Organization, Consolidation and Presentation of Financial Statements [Abstract] |
Number of Customers, Regulated Distribution | customers | 3
Number of Divisions, Regulated Distribution | regulated_gas_distributions_divisions | 6
Number of States in which Entity Operates | state | 8

X
- Definition Number Of Customers, Regulated Distribution + References No definition available. + Details
Name: | ato_NumberOfCustomersRegulatedDistribution
Namespace Prefix: | ato_
Data Type: | xbrli:integerItemType
Balance Type: | na
Period Type: | instant

X
- Definition Represents the number of regulated distribution divisions. + References No definition available. + Details
Name: | ato_NumberOfDivisionsRegulatedDistribution
Namespace Prefix: | ato_
Data Type: | xbrli:integerItemType
Balance Type: | na
Period Type: | instant

X
- Definition The number of states the entity operates in as of the balance sheet date. + References No definition available. + Details
Name: | us-gaap_NumberOfStatesInWhichEntityOperates
Namespace Prefix: | us-gaap_
Data Type: | xbrli:integerItemType
Balance Type: | na
Period Type: | instant

X
- References No definition available. + Details
Name: | us-gaap_OrganizationConsolidationAndPresentationOfFinancialStatementsAbstract
Namespace Prefix: | us-gaap_
Data Type: | xbrli:stringItemType
Balance Type: | na
Period Type: | duration