Significant Accounting Policies All Other - Quarterly (Details) $ in Millions	3 Months Ended
Mar. 31, 2016 USD ($) cowenfund	Dec. 31, 2015 USD ($) cowenfund
Total net assets of consolidated VIEs \| $	$ 452.1	$ 1.5
Deferred rent \| $	11.9	12.0
Deferred Rent Asset, Net, Current \| $	$ 0.3	$ 0.3
Variable Interest Entity, Primary Beneficiary [Member]
Number of funds, Consolidated \| cowenfund	3	3
Other investment companies
Number of funds, Consolidated \| cowenfund	5
Investment Company
Number of funds, Consolidated \| cowenfund	2
Assets Held under Capital Leases [Member]
Property, Plant and Equipment, Useful Life	5 years
Minimum \| Telephone and computer equipment
Property, Plant and Equipment, Useful Life	3 years
Minimum \| Computer Software, Intangible Asset [Member]
Property, Plant and Equipment, Useful Life	3 years
Minimum \| Furniture and Fixtures [Member]
Property, Plant and Equipment, Useful Life	5 years
Minimum \| Leasehold improvements
Property, Plant and Equipment, Useful Life	5 years
Minimum \| Aircraft [Domain]
Property, Plant and Equipment, Useful Life	15 years
Minimum \| Flight Equipment [Member]
Property, Plant and Equipment, Useful Life	4 years
Maximum \| Telephone and computer equipment
Property, Plant and Equipment, Useful Life	8 years
Maximum \| Computer Software, Intangible Asset [Member]
Property, Plant and Equipment, Useful Life	7 years
Maximum \| Furniture and Fixtures [Member]
Property, Plant and Equipment, Useful Life	8 years
Maximum \| Leasehold improvements
Property, Plant and Equipment, Useful Life	15 years
Maximum \| Aircraft [Domain]
Property, Plant and Equipment, Useful Life	20 years
Maximum \| Flight Equipment [Member]
Property, Plant and Equipment, Useful Life	10 years

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- Definition

For a classified balance sheet, the cumulative difference between the rental income or payments required by a lease agreement and the rental income or expense recognized on a straight-line basis, or other systematic and rational basis more representative of the time pattern in which use or benefit is granted or derived from the leased property, expected to be recognized in income or expense, by the lessor or lessee, respectively, within one year (or one operating cycle, if longer) of the balance sheet date. Such receivable is reduced by allowances attributable to, for instance, credit risk associated with a lessee.

+ 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 210.5-02.8)
-URI http://asc.fasb.org/extlink&oid=6877327&loc=d3e13212-122682

Reference 2: http://www.xbrl.org/2003/role/presentationRef
-Publisher FASB
-Name Accounting Standards Codification
-Topic 840
-SubTopic 20
-Section 25
-Paragraph 2
-Subparagraph (a)
-URI http://asc.fasb.org/extlink&oid=7501430&loc=d3e39927-112707

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- Definition

The cumulative difference between the rental payments required by a lease agreement and the rental income or expense recognized on a straight-line basis, or other systematic and rational basis more representative of the time pattern in which use or benefit is granted or derived from the leased property, expected to be recognized in income or expense over the term of the leased property by the lessor or lessee, respectively.

+ References

Reference 1: http://www.xbrl.org/2003/role/presentationRef
-Publisher FASB
-Name Accounting Standards Codification
-Topic 840
-SubTopic 20
-Section 25
-Paragraph 1
-URI http://asc.fasb.org/extlink&oid=7501430&loc=d3e39896-112707

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- Definition

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+ References

No definition available.

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- Definition

The net carrying amount of the consolidated Variable Interest Entity's assets and liabilities included in the reporting entity's statement of financial position.

+ References

No definition available.

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