v3.19.3.a.u2

Summary of significant accounting policies - Equity comp (Details) | 12 Months Ended
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Dec. 31, 2019
Long-term incentive plan |
Equity compensation plans |
Weighted average forfeiture rate | 11.00%

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- Definition Share-based Compensation Arrangement by Share-based Payment Award, Weighted Average Forfeiture Rate + References No definition available. + Details
Name: | at_ShareBasedCompensationArrangementByShareBasedPaymentAwardWeightedAverageForfeitureRate
Namespace Prefix: | at_
Data Type: | num:percentItemType
Balance Type: | na
Period Type: | duration

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

X
- Details
Name: | us-gaap_PlanNameAxis=at_LongTermIncentivePlanMember
Namespace Prefix: |
Data Type: | na
Balance Type: |
Period Type: |