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

X

- Definition

The value of assets that are managed by a company

+ References

No definition available.

+ Details

Name:	amg_ValueOfManagedAssets
Namespace Prefix:	amg_
Data Type:	xbrli:monetaryItemType
Balance Type:	debit
Period Type:	instant

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- Details

Name:	us-gaap_ScheduleOfEquityMethodInvestmentsLineItems
Namespace Prefix:	us-gaap_
Data Type:	xbrli:stringItemType
Balance Type:	na
Period Type:	duration