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v3.5.0.2

Commitments and Contingencies (Details) | Sep. 30, 2016 USD ($)
--- | ---
Commitments and Contingencies |
Co-investment commitments in partnership | $ 91,800,000
Expected payments of contingent liability | 10,300,000
Consolidated Affiliates |
Commitments and Contingencies |
Contingent liability | 84,900,000
Expected payments of contingent liability | 84,900,000
Equity Method Investee |
Commitments and Contingencies |
Contingent liability | 316,500,000
Expected payments of contingent liability | 0
Prior Owner |
Commitments and Contingencies |
Reimbursable amount of investment commitments | $ 14,000,000

X
- Definition -- None. No documentation exists for this element. -- + References No definition available. + Details
Name: | amg_CommitmentAndContingenciesLineItems
Namespace Prefix: | amg_
Data Type: | xbrli:stringItemType
Balance Type: | na
Period Type: | duration

X
- Definition The amount that the entity agreed to co-invest in certain investment partnerships where the entity serves as the general partner. + References No definition available. + Details
Name: | amg_InvestmentCommitmentAmount
Namespace Prefix: | amg_
Data Type: | xbrli:monetaryItemType
Balance Type: | credit
Period Type: | instant

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- Definition Other Commitment Expected Payments + References No definition available. + Details
Name: | amg_OtherCommitmentExpectedPayments
Namespace Prefix: | amg_
Data Type: | xbrli:monetaryItemType
Balance Type: | debit
Period Type: | instant

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- Definition Represents the contractual obligation to reimburse the entity for co-investments in investment partnerships. + References No definition available. + Details
Name: | amg_ReimbursableAmountOfInvestmentCommitments
Namespace Prefix: | amg_
Data Type: | xbrli:monetaryItemType
Balance Type: | debit
Period Type: | instant

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- Definition Minimum amount of other commitment not otherwise specified in the taxonomy. Excludes commitments explicitly modeled in the taxonomy, including but not limited to, long-term and short-term purchase commitments, recorded and unrecorded purchase obligations, supply commitments, registration payment arrangements, leases, debt, product warranties, guarantees, environmental remediation obligations, and pensions. + References No definition available. + Details
Name: | us-gaap_OtherCommitment
Namespace Prefix: | us-gaap_
Data Type: | xbrli:monetaryItemType
Balance Type: | credit
Period Type: | instant

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- Details
Name: | us-gaap_RelatedPartyTransactionsByRelatedPartyAxis=us-gaap_ConsolidatedEntitiesMember
Namespace Prefix: |
Data Type: | na
Balance Type: |
Period Type: |

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- Details
Name: | us-gaap_RelatedPartyTransactionsByRelatedPartyAxis=us-gaap_EquityMethodInvesteeMember
Namespace Prefix: |
Data Type: | na
Balance Type: |
Period Type: |

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- Details
Name: | dei_LegalEntityAxis=amg_PriorOwnerOfPantheonMember
Namespace Prefix: |
Data Type: | na
Balance Type: |
Period Type: |