XML 77 R55.htm IDEA: XBRL DOCUMENT v3.20.4

Investments in Marketable Securities - Additional Information (Details) - USD ($) $ in Millions	Dec. 31, 2020	Dec. 31, 2019
Variable Interest Entity, Primary Beneficiary
Marketable Securities [Line Items]
Fair value of deconsolidated affiliate	$ 52.3	$ 38.1

X

- Definition

Marketable Securities, Fair Value, Deconsolidation

+ References

No definition available.

+ Details

Name:	amg_MarketableSecuritiesFairValueDeconsolidation
Namespace Prefix:	amg_
Data Type:	xbrli:monetaryItemType
Balance Type:	credit
Period Type:	instant

X

- Definition

Line items represent financial concepts included in a table. These concepts are used to disclose reportable information associated with domain members defined in one or many axes to the table.

+ References

No definition available.

+ Details

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

X

- Details

Name:	srt_ConsolidatedEntitiesAxis=us-gaap_VariableInterestEntityPrimaryBeneficiaryMember
Namespace Prefix:
Data Type:	na
Balance Type:
Period Type: