Significant Accounting Policies - Annual (Details) $ in Thousands	12 Months Ended
	Dec. 31, 2015 USD ($) cowenfund	Dec. 31, 2014 USD ($) cowenfund
Organization [Line Items]
Total net assets of consolidated VIEs | $	$ 2,200	$ 2,000
Deferred rent | $	11,979	13,142
Deferred Rent Asset, Net, Current | $	$ 341	$ 512
Minimum
Organization [Line Items]
Redeemable Noncontrolling Interest, Redemption Fee, Percent	1.00%
Maximum
Organization [Line Items]
Redeemable Noncontrolling Interest, Redemption Fee, Percent	5.00%
Telephone and computer equipment | Minimum
Organization [Line Items]
Property, Plant and Equipment, Useful Life	3 years
Telephone and computer equipment | Maximum
Organization [Line Items]
Property, Plant and Equipment, Useful Life	8 years
Computer Software, Intangible Asset [Member] | Minimum
Organization [Line Items]
Property, Plant and Equipment, Useful Life	3 years
Computer Software, Intangible Asset [Member] | Maximum
Organization [Line Items]
Property, Plant and Equipment, Useful Life	5 years
Furniture and Fixtures [Member] | Minimum
Organization [Line Items]
Property, Plant and Equipment, Useful Life	5 years
Furniture and Fixtures [Member] | Maximum
Organization [Line Items]
Property, Plant and Equipment, Useful Life	8 years
Leasehold improvements | Minimum
Organization [Line Items]
Property, Plant and Equipment, Useful Life	5 years
Leasehold improvements | Maximum
Organization [Line Items]
Property, Plant and Equipment, Useful Life	15 years
Assets Held under Capital Leases [Member]
Organization [Line Items]
Property, Plant and Equipment, Useful Life	5 years
Variable Interest Entity, Primary Beneficiary [Member]
Organization [Line Items]
Number of funds, Consolidated | cowenfund	3	2
Other investment companies
Organization [Line Items]
Number of funds, Consolidated | cowenfund	5
Investment Company
Organization [Line Items]
Number of funds, Consolidated | cowenfund	4	4
Managed mutual funds | Minimum
Organization [Line Items]
Asset Management Fees, Percent Fee	1.35%
Managed mutual funds | Maximum
Organization [Line Items]
Asset Management Fees, Percent Fee	1.90%
Alternative Solutions | Maximum
Organization [Line Items]
Asset Management Fees, Percent Fee	2.00%
Real Estate Funds | Minimum
Organization [Line Items]
Asset Management Fees, Percent Fee	0.25%
Real Estate Funds | Maximum
Organization [Line Items]
Asset Management Fees, Percent Fee	1.50%
Hedge Funds | Maximum
Organization [Line Items]
Asset Management Fees, Percent Fee	2.00%
After investment period | Healthcare Royalty Partners
Organization [Line Items]
Asset Management Fees, Percent Fee	2.00%
During investment period | Healthcare Royalty Partners
Organization [Line Items]
Asset Management Fees, Percent Fee	2.00%
Commodity trading advisory | Ramius Trading Strategies Managed Futures Fund | Maximum
Organization [Line Items]
Asset Management Fees, Percent Fee	0.50%
Alternative Solutions
Organization [Line Items]
Incentive Fees, Percent Fee	10.00%
Hedge Funds
Organization [Line Items]
Incentive Fees, Percent Fee	20.00%