XML 139 R101.htm IDEA: XBRL DOCUMENT v2.4.1.9

Benefit Plans (Details) (USD $) In Millions, unless otherwise specified	12 Months Ended
	Dec. 31, 2014 plan	Dec. 31, 2013	Dec. 31, 2012
Compensation and Retirement Disclosure [Abstract]
Number of defined contribution plans	3amg_DefinedContributionPlansNumber
Consolidated expenses related to benefit plans	$ 17.2us-gaap_DefinedContributionPlanCostRecognized	$ 14.1us-gaap_DefinedContributionPlanCostRecognized	$ 12.7us-gaap_DefinedContributionPlanCostRecognized

X

- Definition

The number of defined contribution plans sponsored by the entity.

+ References

No definition available.

+ Details

Name:	amg_DefinedContributionPlansNumber
Namespace Prefix:	amg_
Data Type:	xbrli:integerItemType
Balance Type:	na
Period Type:	duration

X

- Details

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

X

- Definition

The amount of the cost recognized during the period for defined contribution plans.

+ References

Reference 1: http://www.xbrl.org/2003/role/presentationRef

-Publisher FASB

-Name Accounting Standards Codification

-Topic 715

-SubTopic 70

-Section 50

-Paragraph 1

-URI http://asc.fasb.org/extlink&oid=6414718&loc=d3e28014-114942

+ Details

Name:	us-gaap_DefinedContributionPlanCostRecognized
Namespace Prefix:	us-gaap_
Data Type:	xbrli:monetaryItemType
Balance Type:	debit
Period Type:	duration