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Subsequent Events (Details) - Subsequent Event - BlueMountain - Equity Method Investee $ in Billions | Oct. 01, 2019 USD ($)
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Subsequent Event [Line Items] |
Assets under management | $ 18.3
Percentage of outstanding equity interest | 100.00%

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- Definition Equity Method Investment, Outstanding Ownership Percentage Sold + References No definition available. + Details
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Balance Type: | na
Period Type: | duration

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- Definition The carrying amount of assets an investment adviser manages on behalf of investors. + References No definition available. + Details
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Balance Type: | debit
Period Type: | instant

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- Definition Detail information of subsequent event by type. User is expected to use existing line items from elsewhere in the taxonomy as the primary line items for this disclosure, which is further associated with dimension and member elements pertaining to a subsequent event. + References No definition available. + Details
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- Details
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- Details
Name: | dei_LegalEntityAxis=amg_BlueMountainCapitalManagementLLCMember
Namespace Prefix: |
Data Type: | na
Balance Type: |
Period Type: |

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- Details
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