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

Maximum aggregate offering price of common limited partners units under an equity distribution agreement.

No definition available.

Name:	am_CommonLimitedPartnersUnitsDistributionAgreementMaximumAmount
Namespace Prefix:	am_
Data Type:	xbrli:monetaryItemType
Balance Type:	debit
Period Type:	duration

Remaining capacity to issue additional common units under an equity distribution agreement.

No definition available.

Name:	am_CommonLimitedPartnersUnitsDistributionAgreementRemainingCapacity
Namespace Prefix:	am_
Data Type:	xbrli:monetaryItemType
Balance Type:	debit
Period Type:	instant

Total limited partner units issued during the period due to the sale of units.

No definition available.

Name:	am_LimitedPartnersSaleOfUnits
Namespace Prefix:	am_
Data Type:	xbrli:sharesItemType
Balance Type:	na
Period Type:	duration

The amount of compensation payable to the sales agents for sales made during the period.

No definition available.

Name:	am_LimitedPartnersSaleOfUnitsCompensationPayable
Namespace Prefix:	am_
Data Type:	xbrli:monetaryItemType
Balance Type:	debit
Period Type:	duration

The amount of other offering cost.

No definition available.

Name:	am_LimitedPartnersSaleOfUnitsOtherOfferingCost
Namespace Prefix:	am_
Data Type:	xbrli:monetaryItemType
Balance Type:	debit
Period Type:	duration

Total amount of limited partner units issued during the period due to the sale of units.

No definition available.

Name:	am_LimitedPartnersSaleOfUnitsValue
Namespace Prefix:	am_
Data Type:	xbrli:monetaryItemType
Balance Type:	debit
Period Type:	duration

No definition available.

Name:	am_SaleOfCommonUnitsUnderEquityDistributionAgreementAbstract
Namespace Prefix:	am_
Data Type:	xbrli:stringItemType
Balance Type:	na
Period Type:	duration