Investments in Merchant Banking Funds - Additional Information (Details) - USD ($) $ in Millions	Sep. 30, 2015	Dec. 31, 2014
GCP I
Fair Value, Measurement Inputs, Disclosure [Line Items]
Investment related to noncontrolling interests	$ 0.1	$ 0.1
GCP II
Fair Value, Measurement Inputs, Disclosure [Line Items]
Investment related to noncontrolling interests	$ 0.6	$ 0.6

Total of all Partners' Capital (deficit) items which is directly or indirectly attributable to that ownership interest in subsidiary equity which is not attributable to the parent (noncontrolling interest, minority interest).

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

-Publisher FASB

-Name Accounting Standards Codification

-Topic 505

-SubTopic 10

-Section S99

-Paragraph 1

-URI http://asc.fasb.org/extlink&oid=27012166&loc=d3e187085-122770

Reference 2: http://www.xbrl.org/2003/role/presentationRef

-Publisher FASB

-Name Accounting Standards Codification

-Topic 505

-SubTopic 10

-Section S99

-Paragraph 5

-URI http://asc.fasb.org/extlink&oid=27012166&loc=d3e187171-122770

Reference 3: http://www.xbrl.org/2003/role/presentationRef

-Publisher FASB

-Name Accounting Standards Codification

-Topic 272

-SubTopic 10

-Section 50

-Paragraph 1

-URI http://asc.fasb.org/extlink&oid=6373374&loc=d3e70434-108055

Reference 4: http://www.xbrl.org/2003/role/presentationRef

-Publisher SEC

-Name Regulation S-X (SX)

-Number 210

-Section 03

-Paragraph 20

-Article 7

Reference 5: http://www.xbrl.org/2003/role/presentationRef

-Publisher SEC

-Name Regulation S-X (SX)

-Number 210

-Section 02

-Paragraph 27

-Article 5

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Namespace Prefix:	us-gaap_
Data Type:	xbrli:monetaryItemType
Balance Type:	credit
Period Type:	instant