v3.7.0.1

Sale of Common Units Under Equity Distribution Agreement (Details) - USD ($) $ in Millions | 3 Months Ended | 6 Months Ended
--- | --- | ---
Sep. 30, 2016 | Jun. 30, 2017
Sale of Common Units Under Equity Distribution Agreement |  |
Maximum aggregate offering price of common limited partners units under an equity distribution agreement | $ 250.0 |
Units issued and sold (in shares) |  | 700,031
Net proceeds from issue and sale of common units |  | $ 23.1
Remaining capacity to issue additional common units under an equity distribution agreement |  | $ 159.9

X
- Definition Maximum aggregate offering price of common limited partners units under an equity distribution agreement. + References No definition available. + Details
Name: | am_CommonLimitedPartnersUnitsDistributionAgreementMaximumAmount
Namespace Prefix: | am_
Data Type: | xbrli:monetaryItemType
Balance Type: | debit
Period Type: | duration

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- Definition Remaining capacity to issue additional common units under an equity distribution agreement. + References No definition available. + Details
Name: | am_CommonLimitedPartnersUnitsDistributionAgreementRemainingCapacity
Namespace Prefix: | am_
Data Type: | xbrli:monetaryItemType
Balance Type: | debit
Period Type: | instant

X
- Definition Total limited partner units issued during the period due to the sale of units. + References No definition available. + Details
Name: | am_LimitedPartnersSaleOfUnits
Namespace Prefix: | am_
Data Type: | xbrli:sharesItemType
Balance Type: | na
Period Type: | duration

X
- Definition Total amount of limited partner units issued during the period due to the sale of units. + References No definition available. + Details
Name: | am_LimitedPartnersSaleOfUnitsValue
Namespace Prefix: | am_
Data Type: | xbrli:monetaryItemType
Balance Type: | debit
Period Type: | duration

X
- References No definition available. + Details
Name: | am_SaleOfCommonUnitsUnderEquityDistributionAgreementAbstract
Namespace Prefix: | am_
Data Type: | xbrli:stringItemType
Balance Type: | na
Period Type: | duration