<?xml version="1.0" encoding="utf-8"?>
<FilingSummary xmlns:xsi="http://www.w3.org/2001/XMLSchema-instance" xmlns:xsd="http://www.w3.org/2001/XMLSchema">
  <Version>2.3.0.15</Version>
  <ProcessingTime />
  <ReportFormat>Html</ReportFormat>
  <ReportType />
  <ContextCount>55</ContextCount>
  <ElementCount>162</ElementCount>
  <EntityCount>1</EntityCount>
  <FootnotesReported>false</FootnotesReported>
  <SegmentCount>9</SegmentCount>
  <ScenarioCount>0</ScenarioCount>
  <TuplesReported>false</TuplesReported>
  <UnitCount>3</UnitCount>
  <MyReports>
    <Report>
      <IsDefault>true</IsDefault>
      <ContainEmbeddedReports>false</ContainEmbeddedReports>
      <HtmlFileName>R1.htm</HtmlFileName>
      <LongName>00090 - Document - Document And Entity Information</LongName>
      <ReportType>Sheet</ReportType>
      <Role>http://www.atpog.com/role/DocumentDocumentAndEntityInformation</Role>
      <ShortName>Document And Entity Information</ShortName>
    </Report>
    <Report>
      <IsDefault>false</IsDefault>
      <ContainEmbeddedReports>false</ContainEmbeddedReports>
      <HtmlFileName>R2.htm</HtmlFileName>
      <LongName>00100 - Statement - Consolidated Balance Sheets</LongName>
      <ReportType>Sheet</ReportType>
      <Role>http://www.atpog.com/role/StatementConsolidatedBalanceSheets</Role>
      <ShortName>Consolidated Balance Sheets</ShortName>
    </Report>
    <Report>
      <IsDefault>false</IsDefault>
      <ContainEmbeddedReports>false</ContainEmbeddedReports>
      <HtmlFileName>R3.htm</HtmlFileName>
      <LongName>00105 - Statement - Consolidated Balance Sheets (Parenthetical)</LongName>
      <ReportType>Sheet</ReportType>
      <Role>http://www.atpog.com/role/StatementConsolidatedBalanceSheetsParenthetical</Role>
      <ShortName>Consolidated Balance Sheets (Parenthetical)</ShortName>
    </Report>
    <Report>
      <IsDefault>false</IsDefault>
      <ContainEmbeddedReports>false</ContainEmbeddedReports>
      <HtmlFileName>R4.htm</HtmlFileName>
      <LongName>00200 - Statement - Consolidated Statements Of Operations</LongName>
      <ReportType>Sheet</ReportType>
      <Role>http://www.atpog.com/role/StatementConsolidatedStatementsOfOperations</Role>
      <ShortName>Consolidated Statements Of Operations</ShortName>
    </Report>
    <Report>
      <IsDefault>false</IsDefault>
      <ContainEmbeddedReports>false</ContainEmbeddedReports>
      <HtmlFileName>R5.htm</HtmlFileName>
      <LongName>00300 - Statement - Consolidated Statements Of Cash Flows</LongName>
      <ReportType>Sheet</ReportType>
      <Role>http://www.atpog.com/role/StatementConsolidatedStatementsOfCashFlows</Role>
      <ShortName>Consolidated Statements Of Cash Flows</ShortName>
    </Report>
    <Report>
      <IsDefault>false</IsDefault>
      <ContainEmbeddedReports>false</ContainEmbeddedReports>
      <HtmlFileName>R6.htm</HtmlFileName>
      <LongName>00400 - Statement - Consolidated Statements Of Shareholders' Equity And Temporary Equity</LongName>
      <ReportType>Sheet</ReportType>
      <Role>http://www.atpog.com/role/StatementConsolidatedStatementsOfShareholdersEquityAndTemporaryEquity</Role>
      <ShortName>Consolidated Statements Of Shareholders' Equity And Temporary Equity</ShortName>
    </Report>
    <Report>
      <IsDefault>false</IsDefault>
      <ContainEmbeddedReports>false</ContainEmbeddedReports>
      <HtmlFileName>R7.htm</HtmlFileName>
      <LongName>00500 - Statement - Consolidated Statements Of Comprehensive Income (Loss)</LongName>
      <ReportType>Sheet</ReportType>
      <Role>http://www.atpog.com/role/StatementConsolidatedStatementsOfComprehensiveIncomeLoss</Role>
      <ShortName>Consolidated Statements Of Comprehensive Income (Loss)</ShortName>
    </Report>
    <Report>
      <IsDefault>false</IsDefault>
      <ContainEmbeddedReports>false</ContainEmbeddedReports>
      <HtmlFileName>R8.htm</HtmlFileName>
      <LongName>10101 - Disclosure - Organization</LongName>
      <ReportType>Sheet</ReportType>
      <Role>http://www.atpog.com/role/DisclosureOrganization</Role>
      <ShortName>Organization</ShortName>
    </Report>
    <Report>
      <IsDefault>false</IsDefault>
      <ContainEmbeddedReports>false</ContainEmbeddedReports>
      <HtmlFileName>R9.htm</HtmlFileName>
      <LongName>10201 - Disclosure - Recent Accounting Pronouncements</LongName>
      <ReportType>Sheet</ReportType>
      <Role>http://www.atpog.com/role/DisclosureRecentAccountingPronouncements</Role>
      <ShortName>Recent Accounting Pronouncements</ShortName>
    </Report>
    <Report>
      <IsDefault>false</IsDefault>
      <ContainEmbeddedReports>false</ContainEmbeddedReports>
      <HtmlFileName>R10.htm</HtmlFileName>
      <LongName>10301 - Disclosure - Risks And Uncertainties</LongName>
      <ReportType>Sheet</ReportType>
      <Role>http://www.atpog.com/role/DisclosureRisksAndUncertainties</Role>
      <ShortName>Risks And Uncertainties</ShortName>
    </Report>
    <Report>
      <IsDefault>false</IsDefault>
      <ContainEmbeddedReports>false</ContainEmbeddedReports>
      <HtmlFileName>R11.htm</HtmlFileName>
      <LongName>10401 - Disclosure - Oil And Gas Properties</LongName>
      <ReportType>Sheet</ReportType>
      <Role>http://www.atpog.com/role/DisclosureOilAndGasProperties</Role>
      <ShortName>Oil And Gas Properties</ShortName>
    </Report>
    <Report>
      <IsDefault>false</IsDefault>
      <ContainEmbeddedReports>false</ContainEmbeddedReports>
      <HtmlFileName>R12.htm</HtmlFileName>
      <LongName>10501 - Disclosure - Income Taxes</LongName>
      <ReportType>Sheet</ReportType>
      <Role>http://www.atpog.com/role/DisclosureIncomeTaxes</Role>
      <ShortName>Income Taxes</ShortName>
    </Report>
    <Report>
      <IsDefault>false</IsDefault>
      <ContainEmbeddedReports>false</ContainEmbeddedReports>
      <HtmlFileName>R13.htm</HtmlFileName>
      <LongName>10601 - Disclosure - Long-Term Debt</LongName>
      <ReportType>Sheet</ReportType>
      <Role>http://www.atpog.com/role/DisclosureLongTermDebt</Role>
      <ShortName>Long-Term Debt</ShortName>
    </Report>
    <Report>
      <IsDefault>false</IsDefault>
      <ContainEmbeddedReports>false</ContainEmbeddedReports>
      <HtmlFileName>R14.htm</HtmlFileName>
      <LongName>10701 - Disclosure - Other Long-Term Obligations</LongName>
      <ReportType>Sheet</ReportType>
      <Role>http://www.atpog.com/role/DisclosureOtherLongTermObligations</Role>
      <ShortName>Other Long-Term Obligations</ShortName>
    </Report>
    <Report>
      <IsDefault>false</IsDefault>
      <ContainEmbeddedReports>false</ContainEmbeddedReports>
      <HtmlFileName>R15.htm</HtmlFileName>
      <LongName>10801 - Disclosure - Preferred Stock</LongName>
      <ReportType>Sheet</ReportType>
      <Role>http://www.atpog.com/role/DisclosurePreferredStock</Role>
      <ShortName>Preferred Stock</ShortName>
    </Report>
    <Report>
      <IsDefault>false</IsDefault>
      <ContainEmbeddedReports>false</ContainEmbeddedReports>
      <HtmlFileName>R16.htm</HtmlFileName>
      <LongName>10901 - Disclosure - Asset Retirement Obligation</LongName>
      <ReportType>Sheet</ReportType>
      <Role>http://www.atpog.com/role/DisclosureAssetRetirementObligation</Role>
      <ShortName>Asset Retirement Obligation</ShortName>
    </Report>
    <Report>
      <IsDefault>false</IsDefault>
      <ContainEmbeddedReports>false</ContainEmbeddedReports>
      <HtmlFileName>R17.htm</HtmlFileName>
      <LongName>11001 - Disclosure - Stock-Based Compensation</LongName>
      <ReportType>Sheet</ReportType>
      <Role>http://www.atpog.com/role/DisclosureStockBasedCompensation</Role>
      <ShortName>Stock-Based Compensation</ShortName>
    </Report>
    <Report>
      <IsDefault>false</IsDefault>
      <ContainEmbeddedReports>false</ContainEmbeddedReports>
      <HtmlFileName>R18.htm</HtmlFileName>
      <LongName>11101 - Disclosure - Earnings Per Share</LongName>
      <ReportType>Sheet</ReportType>
      <Role>http://www.atpog.com/role/DisclosureEarningsPerShare</Role>
      <ShortName>Earnings Per Share</ShortName>
    </Report>
    <Report>
      <IsDefault>false</IsDefault>
      <ContainEmbeddedReports>false</ContainEmbeddedReports>
      <HtmlFileName>R19.htm</HtmlFileName>
      <LongName>11201 - Disclosure - Derivative Instruments And Risk Management Activities</LongName>
      <ReportType>Sheet</ReportType>
      <Role>http://www.atpog.com/role/DisclosureDerivativeInstrumentsAndRiskManagementActivities</Role>
      <ShortName>Derivative Instruments And Risk Management Activities</ShortName>
    </Report>
    <Report>
      <IsDefault>false</IsDefault>
      <ContainEmbeddedReports>false</ContainEmbeddedReports>
      <HtmlFileName>R20.htm</HtmlFileName>
      <LongName>11301 - Disclosure - Commitments And Contingencies</LongName>
      <ReportType>Sheet</ReportType>
      <Role>http://www.atpog.com/role/DisclosureCommitmentsAndContingencies</Role>
      <ShortName>Commitments And Contingencies</ShortName>
    </Report>
    <Report>
      <IsDefault>false</IsDefault>
      <ContainEmbeddedReports>false</ContainEmbeddedReports>
      <HtmlFileName>R21.htm</HtmlFileName>
      <LongName>11401 - Disclosure - Segment Information</LongName>
      <ReportType>Sheet</ReportType>
      <Role>http://www.atpog.com/role/DisclosureSegmentInformation</Role>
      <ShortName>Segment Information</ShortName>
    </Report>
    <Report>
      <IsDefault>false</IsDefault>
      <ContainEmbeddedReports>false</ContainEmbeddedReports>
      <HtmlFileName>R22.htm</HtmlFileName>
      <LongName>11501 - Disclosure - Fair Value Measurements</LongName>
      <ReportType>Sheet</ReportType>
      <Role>http://www.atpog.com/role/DisclosureFairValueMeasurements</Role>
      <ShortName>Fair Value Measurements</ShortName>
    </Report>
    <Report>
      <IsDefault>false</IsDefault>
      <ContainEmbeddedReports>false</ContainEmbeddedReports>
      <HtmlFileName>R23.htm</HtmlFileName>
      <LongName>11601 - Disclosure - Subsequent Events</LongName>
      <ReportType>Sheet</ReportType>
      <Role>http://www.atpog.com/role/DisclosureSubsequentEvents</Role>
      <ShortName>Subsequent Events</ShortName>
    </Report>
    <Report>
      <IsDefault>false</IsDefault>
      <ContainEmbeddedReports>false</ContainEmbeddedReports>
      <LongName>All Reports</LongName>
      <ReportType>Book</ReportType>
      <ShortName>All Reports</ShortName>
    </Report>
  </MyReports>
  <Logs>
    <Log type="Info">'Monetary' elements on report '00105 - Statement - Consolidated Balance Sheets (Parenthetical)' had a mix of different decimal attribute values.</Log>
    <Log type="Info">Process Flow-Through: 00100 - Statement - Consolidated Balance Sheets</Log>
    <Log type="Info">	Process Flow-Through: Removing column 'Sep. 30, 2010'</Log>
    <Log type="Info">	Process Flow-Through: Removing column 'Dec. 31, 2009'</Log>
    <Log type="Info">Process Flow-Through: 00105 - Statement - Consolidated Balance Sheets (Parenthetical)</Log>
    <Log type="Info">Process Flow-Through: 00200 - Statement - Consolidated Statements Of Operations</Log>
    <Log type="Info">Process Flow-Through: 00300 - Statement - Consolidated Statements Of Cash Flows</Log>
    <Log type="Info">Process Flow-Through: 00500 - Statement - Consolidated Statements Of Comprehensive Income (Loss)</Log>
  </Logs>
  <InputFiles>
    <File>atpg-20110930.xml</File>
    <File>atpg-20110930.xsd</File>
    <File>atpg-20110930_cal.xml</File>
    <File>atpg-20110930_def.xml</File>
    <File>atpg-20110930_lab.xml</File>
    <File>atpg-20110930_pre.xml</File>
  </InputFiles>
  <SupplementalFiles />
  <BaseTaxonomies />
  <HasPresentationLinkbase>true</HasPresentationLinkbase>
  <HasCalculationLinkbase>true</HasCalculationLinkbase>
</FilingSummary>
