Leases - Narrative (Details) $ in Millions	Sep. 30, 2023 USD ($) serviceCenter
Leases [Abstract]
Number of buildings leased, not yet commenced \| serviceCenter	1
Lessee, future payments, not yet commenced \| $	$ 28.9

Lessee, Not Yet Commenced, Number of Buildings Leased

No definition available.

Name:	ato_LesseeNotYetCommencedNumberOfBuildingsLeased
Namespace Prefix:	ato_
Data Type:	xbrli:integerItemType
Balance Type:	na
Period Type:	instant