XML 66 R40.htm IDEA: XBRL DOCUMENT v3.20.2

Investments in Marketable Securities - Cost, Gross Unrealized Gains and Losses and Fair Value (Details) - USD ($) $ in Millions	Jun. 30, 2020	Dec. 31, 2019
Marketable Securities [Abstract]
Cost	$ 62.3	$ 57.9
Unrealized gains	1.7	2.1
Unrealized losses	(2.6)	(0.6)
Fair value	$ 61.4	$ 59.4

X

- Definition

Marketable Securities, Cost

+ References

No definition available.

+ Details

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

X

- Definition

Marketable Securities, Unrealized Gains

+ References

No definition available.

+ Details

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

X

- Definition

Marketable Securities, Unrealized Losses

+ References

No definition available.

+ Details

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

X

- Definition

Amount of investment in marketable security.

+ References

Reference 1: http://fasb.org/us-gaap/role/ref/legacyRef
-Publisher FASB
-Name Accounting Standards Codification
-Topic 942
-SubTopic 210
-Section S99
-Paragraph 1
-Subparagraph (SX 210.9-03.4)
-URI http://asc.fasb.org/extlink&oid=120398452&loc=d3e534808-122878

+ Details

Name:	us-gaap_MarketableSecurities
Namespace Prefix:	us-gaap_
Data Type:	xbrli:monetaryItemType
Balance Type:	debit
Period Type:	instant

X

- References

No definition available.

+ Details

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