v3.5.0.2

Contingencies (Details) | Sep. 30, 2016 item
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Shareholder class action lawsuits |
Contingencies |
Number of pending matters having material adverse impact on financial position or results of operations or have been reserved | 0

X
- Definition Represents the number of pending matters having material adverse impact on financial position or results of operations or have been reserved. + References No definition available. + Details
Name: | at_LossContingencyPendingMattersHavingMaterialAdverseImpactOnFinancialPositionOrResultsOfOperationsOrHaveBeenReserved
Namespace Prefix: | at_
Data Type: | xbrli:integerItemType
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
Name: | us-gaap_LossContingenciesLineItems
Namespace Prefix: | us-gaap_
Data Type: | xbrli:stringItemType
Balance Type: | na
Period Type: | duration

X
- Details
Name: | us-gaap_LossContingenciesByNatureOfContingencyAxis=at_ShareholderClassActionLawsuitsMember
Namespace Prefix: |
Data Type: | na
Balance Type: |
Period Type: |