v2.4.0.6

Goodwill, transmission system rights, power purchase agreements and development intangible assets and liabilities (Details 2) (USD $) In Thousands, unless otherwise specified | 12 Months Ended
--- | ---
Dec. 31, 2012 | Dec. 31, 2011
Components of intangible assets |  |
Gross balance at the end of the period | $ 597,087 | $ 675,330
Less: accumulated amortization | (76,897) | (90,179)
Foreign currency translation adjustment | 4,693 | (877)
Net balance at the end of the period | 524,883 | 584,274
Gross balances at the end of the period | (47,900) | (73,394)
Less: accumulated amortization | 4,448 | 1,371
Foreign currency translation adjustment | (557) | 248
Net balance at the end of the period | (44,009) | (71,775)
Amortization of intangible assets | 65,072 | 10,216
Transmission system rights |  |
Components of intangible assets |  |
Gross balance at the end of the period |  | 231,669
Foreign currency translation adjustment |  | (51,387)
Net balance at the end of the period |  | 180,282
Power Purchase Agreements |  |
Components of intangible assets |  |
Gross balance at the end of the period | 590,923 | 639,699
Less: accumulated amortization | (76,897) | (63,908)
Foreign currency translation adjustment | 4,693 | (877)
Net balance at the end of the period | 518,719 | 574,914
Gross balances at the end of the period | (35,287) | (35,288)
Less: accumulated amortization | 2,884 | 398
Foreign currency translation adjustment | (557) | 127
Net balance at the end of the period | (32,960) | (34,763)
Amortization of intangible assets | 66,168 | 11,586
Fuel Supply Agreements |  |
Components of intangible assets |  |
Gross balance at the end of the period |  | 33,845
Less: accumulated amortization |  | (26,271)
Net balance at the end of the period |  | 7,574
Gross balances at the end of the period | (12,613) | (38,106)
Less: accumulated amortization | 1,564 | 973
Foreign currency translation adjustment |  | 121
Net balance at the end of the period | (11,049) | (37,012)
Amortization of intangible assets | (1,096) | (1,370)
Development Costs |  |
Components of intangible assets |  |
Gross balance at the end of the period | 6,164 | 1,786
Net balance at the end of the period | $ 6,164 | $ 1,786

X
- Definition The accumulated amount of foreign currency translation adjustment of a major finite-lived intangible assets class. + References No definition available. + Details
Name: | at_FiniteLivedIntangibleAssetsForeignCurrencyTranslationAdjustment
Namespace Prefix: | at_
Data Type: | xbrli:monetaryItemType
Balance Type: | debit
Period Type: | instant

X
- Definition The accumulated amount of amortization of a major finite-lived intangible liabilities class. + References No definition available. + Details
Name: | at_FiniteLivedIntangibleLiabilitiesAccumulatedAmortization
Namespace Prefix: | at_
Data Type: | xbrli:monetaryItemType
Balance Type: | debit
Period Type: | instant

X
- Definition The accumulated amount of foreign currency translation adjustment of a major finite-lived intangible liabilities class. + References No definition available. + Details
Name: | at_FiniteLivedIntangibleLiabilitiesForeignCurrencyTranslationAdjustment
Namespace Prefix: | at_
Data Type: | xbrli:monetaryItemType
Balance Type: | credit
Period Type: | instant

X
- Definition Represents the gross carrying value as of the balance sheet date of other intangible liabilities. + References No definition available. + Details
Name: | at_FiniteLivedIntangibleLiabilitiesGross
Namespace Prefix: | at_
Data Type: | xbrli:monetaryItemType
Balance Type: | credit
Period Type: | instant

X
- Definition Represents the carrying value as of the balance sheet date of other intangible liabilities. + References No definition available. + Details
Name: | at_OtherIntangibleLiabilitiesNet
Namespace Prefix: | at_
Data Type: | xbrli:monetaryItemType
Balance Type: | credit
Period Type: | instant

X
- Definition The aggregate expense charged against earnings to allocate the cost of intangible assets (nonphysical assets not used in production) in a systematic and rational manner to the periods expected to benefit from such assets. As a noncash expense, this element is added back to net income when calculating cash provided by or used in operations using the indirect method. + References Reference 1: http://www.xbrl.org/2003/role/presentationRef -Publisher FASB -Name Statement of Financial Accounting Standard (FAS) -Number 142 -Paragraph 45 -Subparagraph a(2) -LegacyDoc This reference is SUPERSEDED by the Accounting Standards Codification effective for interim and annual periods ending after September 15, 2009. This reference is included to help users transition from the previous accounting hierarchy and will be removed from future versions of this taxonomy. 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=6943989&loc=d3e3602-108585 Reference 3: http://www.xbrl.org/2003/role/presentationRef -Publisher FASB -Name Accounting Standards Codification -Topic 350 -SubTopic 30 -Section 45 -Paragraph 2 -URI http://asc.fasb.org/extlink&oid=6388964&loc=d3e16225-109274 Reference 4: http://www.xbrl.org/2003/role/presentationRef -Publisher FASB -Name Accounting Standards Codification -Topic 350 -SubTopic 30 -Section 50 -Paragraph 2 -Subparagraph (a)(2) -URI http://asc.fasb.org/extlink&oid=7658586&loc=d3e16323-109275 + Details
Name: | us-gaap_AmortizationOfIntangibleAssets
Namespace Prefix: | us-gaap_
Data Type: | xbrli:monetaryItemType
Balance Type: | debit
Period Type: | duration

X
- Definition Accumulated amount of amortization of assets, excluding financial assets and goodwill, lacking physical substance with a finite life. + References Reference 1: http://www.xbrl.org/2003/role/presentationRef -Publisher FASB -Name Accounting Standards Codification -Topic 350 -SubTopic 30 -Section 50 -Paragraph 2 -Subparagraph (a)(1) -URI http://asc.fasb.org/extlink&oid=7658586&loc=d3e16323-109275 Reference 2: http://www.xbrl.org/2003/role/presentationRef -Publisher FASB -Name Statement of Financial Accounting Standard (FAS) -Number 142 -Paragraph 45 -Subparagraph a(1) -LegacyDoc This reference is SUPERSEDED by the Accounting Standards Codification effective for interim and annual periods ending after September 15, 2009. This reference is included to help users transition from the previous accounting hierarchy and will be removed from future versions of this taxonomy. + Details
Name: | us-gaap_FiniteLivedIntangibleAssetsAccumulatedAmortization
Namespace Prefix: | us-gaap_
Data Type: | xbrli:monetaryItemType
Balance Type: | credit
Period Type: | instant

X
- Definition Amount before amortization of assets, excluding financial assets and goodwill, lacking physical substance with a finite life. + References Reference 1: http://www.xbrl.org/2003/role/presentationRef -Publisher FASB -Name Accounting Standards Codification -Topic 350 -SubTopic 30 -Section 50 -Paragraph 2 -Subparagraph (a)(1) -URI http://asc.fasb.org/extlink&oid=7658586&loc=d3e16323-109275 Reference 2: http://www.xbrl.org/2003/role/presentationRef -Publisher FASB -Name Statement of Financial Accounting Standard (FAS) -Number 142 -Paragraph 45 -Subparagraph a(1) -LegacyDoc This reference is SUPERSEDED by the Accounting Standards Codification effective for interim and annual periods ending after September 15, 2009. This reference is included to help users transition from the previous accounting hierarchy and will be removed from future versions of this taxonomy. + Details
Name: | us-gaap_FiniteLivedIntangibleAssetsGross
Namespace Prefix: | us-gaap_
Data Type: | xbrli:monetaryItemType
Balance Type: | debit
Period Type: | instant

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

X
- Definition Amount after amortization of assets, excluding financial assets and goodwill, lacking physical substance with a finite life. + References Reference 1: http://www.xbrl.org/2003/role/presentationRef -Publisher FASB -Name Accounting Standards Codification -Topic 350 -SubTopic 30 -Section 50 -Paragraph 2 -Subparagraph (a)(1) -URI http://asc.fasb.org/extlink&oid=7658586&loc=d3e16323-109275 Reference 2: http://www.xbrl.org/2003/role/presentationRef -Publisher FASB -Name Statement of Financial Accounting Standard (FAS) -Number 142 -Paragraph 45 -Subparagraph a(1) -LegacyDoc This reference is SUPERSEDED by the Accounting Standards Codification effective for interim and annual periods ending after September 15, 2009. This reference is included to help users transition from the previous accounting hierarchy and will be removed from future versions of this taxonomy. + Details
Name: | us-gaap_FiniteLivedIntangibleAssetsNet
Namespace Prefix: | us-gaap_
Data Type: | xbrli:monetaryItemType
Balance Type: | debit
Period Type: | instant