v3.4.0.3

Segment and geographic information (Detail) $ in Millions | 3 Months Ended |
--- | --- | ---
Mar. 31, 2016 USD ($) segment | Mar. 31, 2015 USD ($) | Dec. 31, 2015 USD ($)
Segment and geographic information |  |  |
Number of Reportable Segments | segment | 4 |  |
Project revenues | $ 106.4 | $ 111.3 |
Segment assets | 1,660.0 | 1,957.3 | $ 1,674.6
Project Adjusted EBITDA | 62.5 | 58.6 |
Change in fair value of derivative instruments | 1.2 | 1.7 |
Depreciation and amortization | 29.9 | 32.9 |
Interest, net | 2.5 | 2.5 |
Other project expense (income) | 0.2 |  |
Project income | 28.7 | 21.5 |
Administration | 6.1 | 9.4 |
Interest, net | 16.6 | 25.7 |
Foreign exchange loss (gain) | 19.8 | (32.2) |
Other income, net | (2.5) | (1.4) |
(Loss) income from continuing operations before income taxes | (11.3) | 20.0 |
Income tax expense (benefit) | 1.6 | (4.6) |
Loss (income) from continuing operations | (12.9) | 24.6 |
East U.S. |  |  |
Segment and geographic information |  |  |
Project revenues | 39.4 | 37.6 |
Segment assets | 802.5 | 861.5 |
Project Adjusted EBITDA | 30.3 | 26.7 |
Change in fair value of derivative instruments | 0.7 | 2.6 |
Depreciation and amortization | 11.0 | 10.7 |
Interest, net | 2.5 | 2.5 |
Project income | 16.1 | 10.9 |
(Loss) income from continuing operations before income taxes | 16.1 | 10.9 |
Loss (income) from continuing operations | 16.1 | 10.9 |
West U.S. |  |  |
Segment and geographic information |  |  |
Project revenues | 19.1 | 23.0 |
Segment assets | 340.4 | 386.3 |
Project Adjusted EBITDA | 7.5 | 10.0 |
Depreciation and amortization | 9.9 | 9.7 |
Project income | (2.4) | 0.3 |
(Loss) income from continuing operations before income taxes | (2.4) | 0.3 |
Loss (income) from continuing operations | (2.4) | 0.3 |
Canada |  |  |
Segment and geographic information |  |  |
Project revenues | 47.7 | 50.4 |
Segment assets | 439.4 | 618.3 |
Project Adjusted EBITDA | 24.8 | 23.7 |
Change in fair value of derivative instruments | (0.4) | (1.6) |
Depreciation and amortization | 8.8 | 12.3 |
Project income | 16.4 | 13.0 |
(Loss) income from continuing operations before income taxes | 16.4 | 13.0 |
Loss (income) from continuing operations | 16.4 | 13.0 |
Un-Allocated Corporate |  |  |
Segment and geographic information |  |  |
Project revenues | 0.2 | 0.3 |
Segment assets | 77.7 | 91.2 |
Project Adjusted EBITDA | (0.1) | (1.8) |
Change in fair value of derivative instruments | 0.9 | 0.7 |
Depreciation and amortization | 0.2 | 0.2 |
Other project expense (income) | 0.2 |  |
Project income | (1.4) | (2.7) |
Administration | 6.1 | 9.4 |
Interest, net | 16.6 | 25.7 |
Foreign exchange loss (gain) | 19.8 | (32.2) |
Other income, net | (2.5) | (1.4) |
(Loss) income from continuing operations before income taxes | (41.4) | (4.2) |
Income tax expense (benefit) | 1.6 | (4.6) |
Loss (income) from continuing operations | $ (43.0) | $ 0.4 |

X
- Definition The total amount of other project related income (expense), not previously categorized from items that are associated with the entity's normal revenue producing operation. + References No definition available. + Details
Name: | at_OtherProjectRelatedIncomeExpenses
Namespace Prefix: | at_
Data Type: | xbrli:monetaryItemType
Balance Type: | credit
Period Type: | duration

X
- Definition The adjusted result for the period before adjusting interest, taxes, depreciation and amortization (including non-cash impairment charges) and changes in fair value of derivative instruments. + References No definition available. + Details
Name: | at_ProjectAdjustedEarningsBeforeInterestTaxesDepreciationAndAmortization
Namespace Prefix: | at_
Data Type: | xbrli:monetaryItemType
Balance Type: | credit
Period Type: | duration

X
- Definition The net result for the period of deducting project expenses from project revenues. + References No definition available. + Details
Name: | at_ProjectIncomeLoss
Namespace Prefix: | at_
Data Type: | xbrli:monetaryItemType
Balance Type: | credit
Period Type: | duration

X
- Definition The net change in the difference between the fair value and the carrying value, or in the comparative fair values, of derivative instruments presented in segment disclosures, including options, swaps, futures, and forward contracts, held at each balance sheet date, that was included in earnings for the period. + References No definition available. + Details
Name: | at_UnrealizedGainLossOnSegmentDerivatives
Namespace Prefix: | at_
Data Type: | xbrli:monetaryItemType
Balance Type: | credit
Period Type: | duration

X
- Definition Sum of the carrying amounts as of the balance sheet date of all assets that are recognized. Assets are probable future economic benefits obtained or controlled by an entity as a result of past transactions or events. + References Reference 1: http://www.xbrl.org/2003/role/presentationRef -Publisher FASB -Name Accounting Standards Codification -Topic 210 -SubTopic 10 -Section S99 -Paragraph 1 -Subparagraph (SX 210.5-02.18) -URI http://asc.fasb.org/extlink&oid=6877327&loc=d3e13212-122682 Reference 2: http://www.xbrl.org/2003/role/presentationRef -Publisher FASB -Name Accounting Standards Codification -Topic 210 -SubTopic 10 -Section S99 -Paragraph 1 -URI http://asc.fasb.org/extlink&oid=6877327&loc=d3e13212-122682 Reference 3: http://www.xbrl.org/2003/role/presentationRef -Publisher SEC -Name Regulation S-X (SX) -Number 210 -Section 03 -Paragraph 12 -Article 7 + Details
Name: | us-gaap_Assets
Namespace Prefix: | us-gaap_
Data Type: | xbrli:monetaryItemType
Balance Type: | debit
Period Type: | instant

X
- Definition The current period expense charged against earnings on long-lived, physical assets not used in production, and which are not intended for resale, to allocate or recognize the cost of such assets over their useful lives; or to record the reduction in book value of an intangible asset over the benefit period of such asset; or to reflect consumption during the period of an asset that is not used in production. + References Reference 1: http://www.xbrl.org/2003/role/presentationRef -Publisher FASB -Name Accounting Standards Codification -Topic 360 -SubTopic 10 -Section 50 -Paragraph 1 -Subparagraph (a) -URI http://asc.fasb.org/extlink&oid=6391035&loc=d3e2868-110229 Reference 2: http://www.xbrl.org/2003/role/presentationRef -Publisher FASB -Name Accounting Standards Codification -Topic 230 -SubTopic 10 -Section 45 -Paragraph 28 -Subparagraph (b) -URI http://asc.fasb.org/extlink&oid=56944662&loc=d3e3602-108585 + Details
Name: | us-gaap_DepreciationAndAmortization
Namespace Prefix: | us-gaap_
Data Type: | xbrli:monetaryItemType
Balance Type: | debit
Period Type: | duration

X
- Definition The aggregate revenue, whether regulated or unregulated, derived from the generation, transmission and distribution of electricity. + References Reference 1: http://www.xbrl.org/2003/role/presentationRef -Publisher FASB -Name Accounting Standards Codification -Topic 225 -SubTopic 10 -Section S99 -Paragraph 2 -Subparagraph (SX 210.5-03.1(b)) -URI http://asc.fasb.org/extlink&oid=26872669&loc=d3e20235-122688 + Details
Name: | us-gaap_ElectricUtilityRevenue
Namespace Prefix: | us-gaap_
Data Type: | xbrli:monetaryItemType
Balance Type: | credit
Period Type: | duration

X
- Definition Amount before tax of foreign currency transaction realized and unrealized gain (loss) recognized in the income statement. + References Reference 1: http://www.xbrl.org/2003/role/presentationRef -Publisher FASB -Name Accounting Standards Codification -Topic 830 -SubTopic 20 -Section 50 -Paragraph 1 -URI http://asc.fasb.org/extlink&oid=6450222&loc=d3e30840-110895 Reference 2: http://www.xbrl.org/2003/role/presentationRef -Publisher FASB -Name Accounting Standards Codification -Topic 830 -SubTopic 20 -Section 45 -Paragraph 2 -URI http://asc.fasb.org/extlink&oid=6450189&loc=d3e30700-110894 Reference 3: http://www.xbrl.org/2003/role/presentationRef -Publisher FASB -Name Accounting Standards Codification -Topic 830 -SubTopic 20 -Section 45 -Paragraph 1 -URI http://asc.fasb.org/extlink&oid=6450189&loc=d3e30690-110894 + Details
Name: | us-gaap_ForeignCurrencyTransactionGainLossBeforeTax
Namespace Prefix: | us-gaap_
Data Type: | xbrli:monetaryItemType
Balance Type: | credit
Period Type: | duration

X
- Definition The aggregate total of expenses of managing and administering the affairs of an entity, including affiliates of the reporting entity, which are not directly or indirectly associated with the manufacture, sale or creation of a product or product line. + References Reference 1: http://www.xbrl.org/2003/role/presentationRef -Publisher FASB -Name Accounting Standards Codification -Topic 225 -SubTopic 10 -Section S99 -Paragraph 2 -Subparagraph (SX 210.5-03.4) -URI http://asc.fasb.org/extlink&oid=26872669&loc=d3e20235-122688 + Details
Name: | us-gaap_GeneralAndAdministrativeExpense
Namespace Prefix: | us-gaap_
Data Type: | xbrli:monetaryItemType
Balance Type: | debit
Period Type: | duration

X
- Definition This element represents the income or loss from continuing operations attributable to the economic entity which may also be defined as revenue less expenses from ongoing operations, after income or loss from equity method investments, but before income taxes, extraordinary items, and noncontrolling interest. + References Reference 1: http://www.xbrl.org/2003/role/presentationRef -Publisher FASB -Name Accounting Standards Codification -Topic 940 -SubTopic 20 -Section 25 -Paragraph 1 -URI http://asc.fasb.org/extlink&oid=51673353&loc=d3e41242-110953 Reference 2: http://www.xbrl.org/2003/role/presentationRef -Publisher FASB -Name Accounting Standards Codification -Topic 235 -SubTopic 10 -Section S99 -Paragraph 1 -URI http://asc.fasb.org/extlink&oid=26873400&loc=d3e23780-122690 Reference 3: http://www.xbrl.org/2003/role/presentationRef -Publisher SEC -Name Regulation S-X (SX) -Number 210 -Section 03 -Paragraph 10 -Article 5 + Details
Name: | us-gaap_IncomeLossFromContinuingOperationsBeforeIncomeTaxesExtraordinaryItemsNoncontrollingInterest
Namespace Prefix: | us-gaap_
Data Type: | xbrli:monetaryItemType
Balance Type: | credit
Period Type: | duration

X
- Definition This element represents the income or loss from continuing operations attributable to the economic entity which may also be defined as revenue less expenses and taxes from ongoing operations before extraordinary items, and noncontrolling interest. + References Reference 1: http://www.xbrl.org/2003/role/presentationRef -Publisher FASB -Name Accounting Standards Codification -Topic 810 -SubTopic 10 -Section 45 -Paragraph 19 -URI http://asc.fasb.org/extlink&oid=51664549&loc=SL4569616-111683 + Details
Name: | us-gaap_IncomeLossFromContinuingOperationsIncludingPortionAttributableToNoncontrollingInterest
Namespace Prefix: | us-gaap_
Data Type: | xbrli:monetaryItemType
Balance Type: | credit
Period Type: | duration

X
- Definition Amount of current income tax expense (benefit) and deferred income tax expense (benefit) pertaining to continuing operations. + References Reference 1: http://www.xbrl.org/2003/role/presentationRef -Publisher FASB -Name Accounting Standards Codification -Topic 740 -SubTopic 10 -Section 50 -Paragraph 9 -Subparagraph (a),(b) -URI http://asc.fasb.org/extlink&oid=6907707&loc=d3e32639-109319 Reference 2: http://www.xbrl.org/2003/role/presentationRef -Publisher FASB -Name Accounting Standards Codification -Topic 235 -SubTopic 10 -Section S99 -Paragraph 1 -Subparagraph (SX 210.4-08.(h)) -URI http://asc.fasb.org/extlink&oid=26873400&loc=d3e23780-122690 Reference 3: http://www.xbrl.org/2003/role/presentationRef -Publisher FASB -Name Accounting Standards Codification -Glossary Income Tax Expense (or Benefit) -URI http://asc.fasb.org/extlink&oid=6515339 + Details
Name: | us-gaap_IncomeTaxExpenseBenefit
Namespace Prefix: | us-gaap_
Data Type: | xbrli:monetaryItemType
Balance Type: | debit
Period Type: | duration

X
- Definition The net amount of nonoperating interest income (expense). + References No definition available. + Details
Name: | us-gaap_InterestIncomeExpenseNonoperatingNet
Namespace Prefix: | us-gaap_
Data Type: | xbrli:monetaryItemType
Balance Type: | credit
Period Type: | duration

X
- Definition Amount of interest revenue (income derived from investments in debt securities and on cash and cash equivalents) net of interest expense (cost of borrowed funds accounted for as interest). + References No definition available. + Details
Name: | us-gaap_InterestRevenueExpenseNet
Namespace Prefix: | us-gaap_
Data Type: | xbrli:monetaryItemType
Balance Type: | credit
Period Type: | duration

X
- Definition Number of segments reported by the entity. A reportable segment is a component of an entity for which there is an accounting requirement to report separate financial information on that component in the entity's financial statements. + References No definition available. + Details
Name: | us-gaap_NumberOfReportableSegments
Namespace Prefix: | us-gaap_
Data Type: | xbrli:integerItemType
Balance Type: | na
Period Type: | duration

X
- Definition The net amount of other income and expense amounts, the components of which are not separately disclosed on the income statement, resulting from ancillary business-related activities (that is, excluding major activities considered part of the normal operations of the business) also known as other nonoperating income (expense) recognized for the period. Such amounts may include: (a) dividends, (b) interest on securities, (c) net gains or losses on securities, (d) unusual costs, (e) gains or losses on foreign exchange transactions, and (f) miscellaneous other income and expense items. + References Reference 1: http://www.xbrl.org/2003/role/presentationRef -Publisher FASB -Name Accounting Standards Codification -Topic 225 -SubTopic 10 -Section S99 -Paragraph 2 -Subparagraph (SX 210.5-03.9) -URI http://asc.fasb.org/extlink&oid=26872669&loc=d3e20235-122688 + Details
Name: | us-gaap_OtherNonoperatingIncomeExpense
Namespace Prefix: | us-gaap_
Data Type: | xbrli:monetaryItemType
Balance Type: | credit
Period Type: | duration

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

X
- Details
Name: | us-gaap_StatementBusinessSegmentsAxis=at_EastSegmentMember
Namespace Prefix: |
Data Type: | na
Balance Type: |
Period Type: |

X
- Details
Name: | us-gaap_StatementBusinessSegmentsAxis=at_WestSegmentMember
Namespace Prefix: |
Data Type: | na
Balance Type: |
Period Type: |

X
- Details
Name: | us-gaap_StatementBusinessSegmentsAxis=at_CanadaSegmentMember
Namespace Prefix: |
Data Type: | na
Balance Type: |
Period Type: |

X
- Details
Name: | us-gaap_StatementBusinessSegmentsAxis=us-gaap_CorporateMember
Namespace Prefix: |
Data Type: | na
Balance Type: |
Period Type: |