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Pending Investments (Details) (USD $) In Billions, unless otherwise specified | Mar. 31, 2012
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Veritable, LP |
Pending Investments |
Value of managed assets | $ 11.1
Yacktman Asset Management Co |
Pending Investments |
Value of managed assets | $ 16.8

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- Definition The value of assets that are managed by a company + References No definition available. + Details
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Namespace Prefix: | amg_
Data Type: | xbrli:monetaryItemType
Balance Type: | debit
Period Type: | instant

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- Details
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Namespace Prefix: | us-gaap_
Data Type: | xbrli:stringItemType
Balance Type: | na
Period Type: | duration