v3.8.0.1

Related Party Transactions (Details) - USD ($) $ in Millions | 3 Months Ended | 9 Months Ended
--- | --- | ---
Sep. 30, 2017 | Sep. 30, 2016 | Sep. 30, 2017 | Sep. 30, 2016
Allocation of costs |  |  |  |
Direct labor expenses | $ 2.6 | $ 1.0 | $ 5.0 | $ 2.8
General and administrative expense | $ 13.0 | $ 12.2 | $ 39.8 | $ 36.1

X
- Definition Represents allocation of costs. + References No definition available. + Details
Name: | am_AllocationOfCosts
Namespace Prefix: | am_
Data Type: | xbrli:stringItemType
Balance Type: | na
Period Type: | duration

X
- Definition Payroll costs incurred (including equity-based compensation) that are directly related to services rendered by an entity during the reporting period. + References Reference 1: http://www.xbrl.org/2003/role/presentationRef -Publisher FASB -Name Accounting Standards Codification -Topic 225 -SubTopic 10 -Section S99 -Paragraph 2 -Subparagraph (SX 210.5-03.2(d)) -URI http://asc.fasb.org/extlink&oid=63488584&loc=d3e20235-122688 + Details
Name: | us-gaap_CostOfServicesDirectLabor
Namespace Prefix: | us-gaap_
Data Type: | xbrli:monetaryItemType
Balance Type: | debit
Period Type: | duration

X
- Definition Amount of selling, general and administrative expenses resulting from transactions, excluding transactions that are eliminated in consolidated or combined financial statements, with related party. + References No definition available. + Details
Name: | us-gaap_RelatedPartyTransactionSellingGeneralAndAdministrativeExpensesFromTransactionsWithRelatedParty
Namespace Prefix: | us-gaap_
Data Type: | xbrli:monetaryItemType
Balance Type: | debit
Period Type: | duration