Investments of Operating Entities and Consolidated Funds - Other Investments (Details) (USD $) In Thousands, unless otherwise specified	12 Months Ended
Dec. 31, 2014	Dec. 31, 2013	Dec. 31, 2012
Investment Holdings [Line Items]
Net Realized gains (losses) on investments, Consolidated Funds	$ 1,861	$ 6,050	$ (8,121)
Other investments	167,464us-gaap_OtherInvestments	99,483us-gaap_OtherInvestments
Other investments	189,377cown_OtherInvestmentsConsolidatedFunds	187,480cown_OtherInvestmentsConsolidatedFunds
Net unrealized gains (losses) on investments, Consolidated Funds	11,029	4,628	14,497
Net realized gains (losses) on derivatives, Consolidated Funds	2,250	521	915
Net unrealized gains (losses) on derivatives, Consolidated Funds	201	(156)	(38)
Real Estate Equity Investment
Investment Holdings [Line Items]
Other investments	2,175	2,088
Portfolio Funds, at fair value
Investment Holdings [Line Items]
Other investments	103,466	71,051
Other investments	188,884	182,638
Equity Method Investments
Investment Holdings [Line Items]
Other investments	61,443	25,966
Lehman claims, at fair value
Investment Holdings [Line Items]
Other investments	380	378
Other investments	493	4,842
RCG RE Manager, LLC \| Real Estate Equity Investment
Investment Holdings [Line Items]
Other investments	$ 2,200	$ 2,100

The net realized gains (losses) on derivatives earned from consolidated funds.

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The net realized gains (losses) on investments earned from the consolidated funds.

+ References

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The net unrealized gains (losses) on derivatives earned from the consolidated funds.

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The net unrealized gains (losses) on investments earned from the consolidated funds.

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Related to consolidated funds only - Other investments not otherwise specified in the taxonomy.

+ References

No definition available.

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Other investments not otherwise specified in the taxonomy.

+ References

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

-Publisher FASB

-Name Accounting Standards Codification

-Topic 210

-SubTopic 10

-Section S99

-Paragraph 1

-Subparagraph (SX 210.5-02.12)

-URI http://asc.fasb.org/extlink&oid=6877327&loc=d3e13212-122682

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

-Publisher SEC

-Name Regulation S-X (SX)

-Number 210

-Section 02

-Paragraph 12

-Article 5

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

-Publisher SEC

-Name Regulation S-X (SX)

-Number 210

-Section 03

-Paragraph 1

-Subparagraph g

-Article 7

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

-Publisher FASB

-Name Accounting Standards Codification

-Topic 944

-SubTopic 210

-Section S99

-Paragraph 1

-Subparagraph (SX 210.7-03.1(f,g))

-URI http://asc.fasb.org/extlink&oid=6879938&loc=d3e572229-122910

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