Annual report pursuant to Section 13 and 15(d)

Long-term Debt (Details)

v2.4.1.9
Long-term Debt (Details) (USD $)
0 Months Ended 12 Months Ended
Nov. 10, 2014
Dec. 31, 2014
Line of credit | Gathering and compression assets    
Long-term debt    
Outstanding balance 510,000,000us-gaap_LineOfCredit
/ us-gaap_CreditFacilityAxis
= us-gaap_LineOfCreditMember
/ us-gaap_PropertyPlantAndEquipmentByTypeAxis
= am_GatheringAndCompressionAssetsMember
 
Line of credit | Minimum | Predecessor    
Long-term debt    
Commitment fees on the unused portion (as a percent)   0.375%us-gaap_LineOfCreditFacilityUnusedCapacityCommitmentFeePercentage
/ us-gaap_CreditFacilityAxis
= us-gaap_LineOfCreditMember
/ us-gaap_RangeAxis
= us-gaap_MinimumMember
/ us-gaap_StatementScenarioAxis
= us-gaap_PredecessorMember
Line of credit | Minimum | LIBOR | Predecessor    
Long-term debt    
Basis spread on variable rate (as a percent)   1.50%us-gaap_DebtInstrumentBasisSpreadOnVariableRate1
/ us-gaap_CreditFacilityAxis
= us-gaap_LineOfCreditMember
/ us-gaap_RangeAxis
= us-gaap_MinimumMember
/ us-gaap_StatementScenarioAxis
= us-gaap_PredecessorMember
/ us-gaap_VariableRateAxis
= us-gaap_LondonInterbankOfferedRateLIBORMember
Line of credit | Minimum | Prime rate | Predecessor    
Long-term debt    
Basis spread on variable rate (as a percent)   0.50%us-gaap_DebtInstrumentBasisSpreadOnVariableRate1
/ us-gaap_CreditFacilityAxis
= us-gaap_LineOfCreditMember
/ us-gaap_RangeAxis
= us-gaap_MinimumMember
/ us-gaap_StatementScenarioAxis
= us-gaap_PredecessorMember
/ us-gaap_VariableRateAxis
= us-gaap_PrimeRateMember
Line of credit | Maximum | Predecessor    
Long-term debt    
Commitment fees on the unused portion (as a percent)   0.50%us-gaap_LineOfCreditFacilityUnusedCapacityCommitmentFeePercentage
/ us-gaap_CreditFacilityAxis
= us-gaap_LineOfCreditMember
/ us-gaap_RangeAxis
= us-gaap_MaximumMember
/ us-gaap_StatementScenarioAxis
= us-gaap_PredecessorMember
Line of credit | Maximum | LIBOR | Predecessor    
Long-term debt    
Basis spread on variable rate (as a percent)   2.50%us-gaap_DebtInstrumentBasisSpreadOnVariableRate1
/ us-gaap_CreditFacilityAxis
= us-gaap_LineOfCreditMember
/ us-gaap_RangeAxis
= us-gaap_MaximumMember
/ us-gaap_StatementScenarioAxis
= us-gaap_PredecessorMember
/ us-gaap_VariableRateAxis
= us-gaap_LondonInterbankOfferedRateLIBORMember
Line of credit | Maximum | Prime rate | Predecessor    
Long-term debt    
Basis spread on variable rate (as a percent)   1.50%us-gaap_DebtInstrumentBasisSpreadOnVariableRate1
/ us-gaap_CreditFacilityAxis
= us-gaap_LineOfCreditMember
/ us-gaap_RangeAxis
= us-gaap_MaximumMember
/ us-gaap_StatementScenarioAxis
= us-gaap_PredecessorMember
/ us-gaap_VariableRateAxis
= us-gaap_PrimeRateMember
New revolving credit facility    
Long-term debt    
Maximum amount of the Credit Facility   1,000,000,000us-gaap_LineOfCreditFacilityMaximumBorrowingCapacity
/ us-gaap_CreditFacilityAxis
= us-gaap_RevolvingCreditFacilityMember
Interest coverage ratio 2.5am_DebtInstrumentCovenantInterestCoverageRatio
/ us-gaap_CreditFacilityAxis
= us-gaap_RevolvingCreditFacilityMember
 
Consolidated total leverage ratio 5.0am_DebtInstrumentCovenantLeverageRatio
/ us-gaap_CreditFacilityAxis
= us-gaap_RevolvingCreditFacilityMember
 
Consolidated total leverage ratio after electing to issue high yield notes 5.25am_DebtInstrumentCovenantLeverageRatioAfterElectingToIssueNotes
/ us-gaap_CreditFacilityAxis
= us-gaap_RevolvingCreditFacilityMember
 
Period of fiscal quarter after a material acquisition considered in leverage ratio 2am_DebtInstrumentCovenantPeriodOfQuarterAfterMaterialAcquisitionConsideredInLeverageRatio
/ us-gaap_CreditFacilityAxis
= us-gaap_RevolvingCreditFacilityMember
 
Consolidated total leverage ratio after a material acquisition 5.50am_DebtInstrumentCovenantLeverageRatioAfterMaterialAcquisition
/ us-gaap_CreditFacilityAxis
= us-gaap_RevolvingCreditFacilityMember
 
Consolidated senior secured leverage ratio 3.75am_DebtInstrumentCovenantSeniorSecuredLeverageRatio
/ us-gaap_CreditFacilityAxis
= us-gaap_RevolvingCreditFacilityMember
 
New revolving credit facility | LIBOR | Base rate loans    
Long-term debt    
Description of variable rate basis   LIBOR
New revolving credit facility | Reference rate | Base rate loans    
Long-term debt    
Description of variable rate basis   the agent bank's reference rate
New revolving credit facility | Federal funds effective rate | Base rate loans    
Long-term debt    
Description of variable rate basis   the federal funds effective rate
Basis spread on variable rate (as a percent) 0.50%us-gaap_DebtInstrumentBasisSpreadOnVariableRate1
/ us-gaap_CreditFacilityAxis
= us-gaap_RevolvingCreditFacilityMember
/ us-gaap_DebtInstrumentAxis
= am_BaseRateLoansMember
/ us-gaap_VariableRateAxis
= us-gaap_FederalFundsEffectiveSwapRateMember
 
New revolving credit facility | One month Eurodollar rate | Base rate loans    
Long-term debt    
Description of variable rate basis   one month Eurodollar
Basis spread on variable rate (as a percent) 1.00%us-gaap_DebtInstrumentBasisSpreadOnVariableRate1
/ us-gaap_CreditFacilityAxis
= us-gaap_RevolvingCreditFacilityMember
/ us-gaap_DebtInstrumentAxis
= am_BaseRateLoansMember
/ us-gaap_VariableRateAxis
= us-gaap_EurodollarMember
 
New revolving credit facility | Minimum | LIBOR | Eurodollar loans    
Long-term debt    
Basis spread on variable rate (as a percent) 1.50%us-gaap_DebtInstrumentBasisSpreadOnVariableRate1
/ us-gaap_CreditFacilityAxis
= us-gaap_RevolvingCreditFacilityMember
/ us-gaap_DebtInstrumentAxis
= am_EurodollarLoansMember
/ us-gaap_RangeAxis
= us-gaap_MinimumMember
/ us-gaap_VariableRateAxis
= us-gaap_LondonInterbankOfferedRateLIBORMember
 
New revolving credit facility | Minimum | One month Eurodollar rate | Base rate loans    
Long-term debt    
Additional spread on variable rate (as a percent) 0.50%am_DebtInstrumentAdditionalSpreadOnVariableRate
/ us-gaap_CreditFacilityAxis
= us-gaap_RevolvingCreditFacilityMember
/ us-gaap_DebtInstrumentAxis
= am_BaseRateLoansMember
/ us-gaap_RangeAxis
= us-gaap_MinimumMember
/ us-gaap_VariableRateAxis
= us-gaap_EurodollarMember
 
New revolving credit facility | Maximum | LIBOR | Eurodollar loans    
Long-term debt    
Basis spread on variable rate (as a percent) 2.25%us-gaap_DebtInstrumentBasisSpreadOnVariableRate1
/ us-gaap_CreditFacilityAxis
= us-gaap_RevolvingCreditFacilityMember
/ us-gaap_DebtInstrumentAxis
= am_EurodollarLoansMember
/ us-gaap_RangeAxis
= us-gaap_MaximumMember
/ us-gaap_VariableRateAxis
= us-gaap_LondonInterbankOfferedRateLIBORMember
 
New revolving credit facility | Maximum | One month Eurodollar rate | Base rate loans    
Long-term debt    
Additional spread on variable rate (as a percent) 1.25%am_DebtInstrumentAdditionalSpreadOnVariableRate
/ us-gaap_CreditFacilityAxis
= us-gaap_RevolvingCreditFacilityMember
/ us-gaap_DebtInstrumentAxis
= am_BaseRateLoansMember
/ us-gaap_RangeAxis
= us-gaap_MaximumMember
/ us-gaap_VariableRateAxis
= us-gaap_EurodollarMember
 
Letter of credit    
Long-term debt    
Current borrowing capacity   150,000,000us-gaap_LineOfCreditFacilityCurrentBorrowingCapacity
/ us-gaap_CreditFacilityAxis
= us-gaap_LetterOfCreditMember