v2.4.0.6

Commitments and contingencies (Details 2) (USD $) In Millions, unless otherwise specified |  | 1 Months Ended
--- | --- | ---
Nov. 26, 2012 Lake | Mar. 31, 2012 Rate application filed with FERC | Feb. 28, 2011 Rate application filed with FERC
Commitments and contingencies |  |  |
Payment to be received under a settlement agreement | $ 5 |  |
Path 15's annual revenue requirement |  | $ 28.8 | $ 30.3

X
- Definition Represents the payment to be received under the settlement agreement. + References No definition available. + Details
Name: | at_GainContingencyPaymentToBeReceivedUnderSettlementAgreement
Namespace Prefix: | at_
Data Type: | xbrli:monetaryItemType
Balance Type: | credit
Period Type: | instant

X
- Definition Represents the amount of annual revenue requirement included in rate application filed. + References No definition available. + Details
Name: | at_LossContingencyAnnualRevenueRequirement
Namespace Prefix: | at_
Data Type: | xbrli:monetaryItemType
Balance Type: | credit
Period Type: | duration

X
- Details
Name: | us-gaap_LossContingenciesLineItems
Namespace Prefix: | us-gaap_
Data Type: | xbrli:stringItemType
Balance Type: | na
Period Type: | duration