Annual report pursuant to Section 13 and 15(d)

Partnership Equity and Distributions (Details)

v2.4.1.9
Partnership Equity and Distributions (Details) (USD $)
In Millions, except Per Share data, unless otherwise specified
0 Months Ended 2 Months Ended 3 Months Ended 12 Months Ended
Feb. 02, 2015
Dec. 31, 2014
Dec. 31, 2014
Dec. 31, 2014
Partnership equity and distributions        
Annual cash distribution (per unit)   0.68am_LimitedPartnerMinimumAnnualDistributionPerPartnershipAgreement    
Cash balance to be maintained for distribution per quarter   $ 26am_CashAvailableForDistributionsPerQuarter    
Cash balance to be maintained for distribution per year   $ 105am_CashAvailableForDistributionsPerYear    
Pro rata cash distribution to the holders of common and subordinate units   0.1955am_LimitedPartnersProRataDistributionToHoldersOfCommonAndSubordinatedUnits    
Distribution Made to Limited Partner, Distributions Declared, Per Unit $ 0.0943us-gaap_DistributionMadeToLimitedPartnerDistributionsDeclaredPerUnit   $ 0.0943us-gaap_DistributionMadeToLimitedPartnerDistributionsDeclaredPerUnit  
Above $0.1955 up to $0.2125 (Member)        
Partnership equity and distributions        
Unitholders marginal percentage interest in distribution       85.00%am_UnitHoldersMarginalPercentageInterestInDistributionPercentageOfLimitedPartnerInterest
/ am_TotalQuarterlyDistributionTargetAmountAxis
= am_Above0.1955UpTo0.2125Member
General Partners marginal percentage interest in distribution       15.00%am_IncentiveDistributionDistributionPercentage
/ am_TotalQuarterlyDistributionTargetAmountAxis
= am_Above0.1955UpTo0.2125Member
Above $0.2125 up to $0.2550 (Member)        
Partnership equity and distributions        
Unitholders marginal percentage interest in distribution       75.00%am_UnitHoldersMarginalPercentageInterestInDistributionPercentageOfLimitedPartnerInterest
/ am_TotalQuarterlyDistributionTargetAmountAxis
= am_Above0.2125UpTo0.2550Member
General Partners marginal percentage interest in distribution       25.00%am_IncentiveDistributionDistributionPercentage
/ am_TotalQuarterlyDistributionTargetAmountAxis
= am_Above0.2125UpTo0.2550Member
Above $0.2550 (Member)        
Partnership equity and distributions        
Pro rata cash distribution to the holders of common and subordinate units       0.2550am_LimitedPartnersProRataDistributionToHoldersOfCommonAndSubordinatedUnits
/ am_TotalQuarterlyDistributionTargetAmountAxis
= am_Above0.2550Member
Unitholders marginal percentage interest in distribution       50.00%am_UnitHoldersMarginalPercentageInterestInDistributionPercentageOfLimitedPartnerInterest
/ am_TotalQuarterlyDistributionTargetAmountAxis
= am_Above0.2550Member
General Partners marginal percentage interest in distribution       50.00%am_IncentiveDistributionDistributionPercentage
/ am_TotalQuarterlyDistributionTargetAmountAxis
= am_Above0.2550Member
Minimum        
Partnership equity and distributions        
Minimum quarterly cash distribution (per unit)   0.17am_LimitedPartnerMinimumQuarterlyDistributionPerPartnershipAgreement
/ us-gaap_RangeAxis
= us-gaap_MinimumMember
   
Minimum | Above $0.1955 up to $0.2125 (Member)        
Partnership equity and distributions        
Pro rata cash distribution to the holders of common and subordinate units       0.1955am_LimitedPartnersProRataDistributionToHoldersOfCommonAndSubordinatedUnits
/ us-gaap_RangeAxis
= us-gaap_MinimumMember
/ am_TotalQuarterlyDistributionTargetAmountAxis
= am_Above0.1955UpTo0.2125Member
Minimum | Above $0.2125 up to $0.2550 (Member)        
Partnership equity and distributions        
Pro rata cash distribution to the holders of common and subordinate units       0.2125am_LimitedPartnersProRataDistributionToHoldersOfCommonAndSubordinatedUnits
/ us-gaap_RangeAxis
= us-gaap_MinimumMember
/ am_TotalQuarterlyDistributionTargetAmountAxis
= am_Above0.2125UpTo0.2550Member
Maximum | Above $0.1955 up to $0.2125 (Member)        
Partnership equity and distributions        
Pro rata cash distribution to the holders of common and subordinate units       0.2125am_LimitedPartnersProRataDistributionToHoldersOfCommonAndSubordinatedUnits
/ us-gaap_RangeAxis
= us-gaap_MaximumMember
/ am_TotalQuarterlyDistributionTargetAmountAxis
= am_Above0.1955UpTo0.2125Member
Maximum | Above $0.2125 up to $0.2550 (Member)        
Partnership equity and distributions        
Pro rata cash distribution to the holders of common and subordinate units       0.2550am_LimitedPartnersProRataDistributionToHoldersOfCommonAndSubordinatedUnits
/ us-gaap_RangeAxis
= us-gaap_MaximumMember
/ am_TotalQuarterlyDistributionTargetAmountAxis
= am_Above0.2125UpTo0.2550Member