v3.20.1

Nature of business (Details) MW in Thousands | 3 Months Ended
--- | ---
Mar. 31, 2020 state region project MW
Nature of business |
Number of states in which power generation projects operate | state | 11
Number of provinces in which power generation projects operate | region | 2
Number of power generation projects | project | 21
Gross generating capacity of project (in MW) | MW | 1,723
Ownership interest in power generation projects (in MW) | MW | 1,327
Number of projects which are majority owned | project | 16

X
- Definition Represents the gross power generating capacity of project. + References No definition available. + Details
Name: | at_GrossGeneratingCapacityOfProject
Namespace Prefix: | at_
Data Type: | num:powerItemType
Balance Type: | na
Period Type: | duration

X
- Definition Represents the number of power generation projects. + References No definition available. + Details
Name: | at_NumberOfOperationalPowerGenerationProjects
Namespace Prefix: | at_
Data Type: | xbrli:integerItemType
Balance Type: | na
Period Type: | instant

X
- Definition Represents the number of power generation projects which are wholly-owned subsidiaries of the reporting entity. + References No definition available. + Details
Name: | at_NumberOfProjectsWhichAreWhollyOwnedSubsidiaries
Namespace Prefix: | at_
Data Type: | xbrli:integerItemType
Balance Type: | na
Period Type: | instant

X
- Definition The number of provinces in which the power generation projects operate. + References No definition available. + Details
Name: | at_NumberOfProvincesInWhichPowerGenerationProjectsOperate
Namespace Prefix: | at_
Data Type: | xbrli:integerItemType
Balance Type: | na
Period Type: | instant

X
- Definition Represents the ownership interest in power generation projects. + References No definition available. + Details
Name: | at_OwnershipInterestInOperationalPowerGenerationProjects
Namespace Prefix: | at_
Data Type: | num:powerItemType
Balance Type: | na
Period Type: | duration

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