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LONG-TERM DEBT - Covenants tested on an annual basis (Details) - OneVI Debt	Sep. 30, 2025
Years 1-3
Short-Term Debt [Line Items]
Annual principal repayment	8.00%
Years 4-6
Short-Term Debt [Line Items]
Annual principal repayment	10.00%
Years 7-8
Short-Term Debt [Line Items]
Annual principal repayment	15.00%
Year 9
Short-Term Debt [Line Items]
Annual principal repayment	18.00%

X

- Definition

Percentage of annual principal repayment for debt instrument.

+ References

No definition available.

+ Details

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Namespace Prefix:	atni_
Data Type:	dtr-types:percentItemType
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

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

X

- Details

Name:	us-gaap_DebtInstrumentAxis=atni_OneviDebtMember
Namespace Prefix:
Data Type:	na
Balance Type:
Period Type:

X

- Details

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Namespace Prefix:
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Balance Type:
Period Type:

X

- Details

Name:	srt_StatementScenarioAxis=atni_PaymentOnFourthToSixthYearMember
Namespace Prefix:
Data Type:	na
Balance Type:
Period Type:

X

- Details

Name:	srt_StatementScenarioAxis=atni_PaymentOnSeventhToEighthYearMember
Namespace Prefix:
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Balance Type:
Period Type:

X

- Details

Name:	srt_StatementScenarioAxis=atni_PaymentOnNinthYearMember
Namespace Prefix:
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Balance Type:
Period Type: