v3.8.0.1

Sale of Common Units Under Equity Distribution Agreement (Details) - USD ($) $ in Millions | 3 Months Ended | 9 Months Ended
--- | --- | ---
Sep. 30, 2016 | Sep. 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) |  | 777,262
Net proceeds from issue and sale of common units |  | $ 25.5
Compensation payable |  | 0.6
Other offering costs |  | 0.4
Remaining capacity to issue additional common units under an equity distribution agreement |  | $ 157.3

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

X
- 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 The amount of compensation payable to the sales agents for sales made during the period. + References No definition available. + Details
Name: | am_LimitedPartnersSaleOfUnitsCompensationPayable
Namespace Prefix: | am_
Data Type: | xbrli:monetaryItemType
Balance Type: | debit
Period Type: | duration

X
- Definition The amount of other offering cost. + References No definition available. + Details
Name: | am_LimitedPartnersSaleOfUnitsOtherOfferingCost
Namespace Prefix: | am_
Data Type: | xbrli:monetaryItemType
Balance Type: | debit
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