Commitments and Contingencies Schedules of Unfunded Commitments (Details) $ in Millions	12 Months Ended
	Dec. 31, 2016 USD ($) cowenfund
Unfunded Commitments
Other Commitments [Line Items]
Number of Real Estate Investments | cowenfund	5
Real Estate Funds
Other Commitments [Line Items]
Other commitments, unfunded amount	$ 7.6	[1]
Real Estate Funds | Commitment to Invest
Other Commitments [Line Items]
Term of capital commitment	3 years
Healthcare Royalty Partners
Other Commitments [Line Items]
Other commitments, unfunded amount	$ 7.3	[2]
Healthcare Royalty Partners | Commitment to Invest
Other Commitments [Line Items]
Term of capital commitment	2 years
Formation 8 Partners Hardware Fund I, L.P. [Member]
Other Commitments [Line Items]
Other commitments, unfunded amount	$ 0.8
Formation 8 Partners Hardware Fund I, L.P. [Member] | Commitment to Invest
Other Commitments [Line Items]
Term of capital commitment	7 years
Lagunita Biosciences, LLC
Other Commitments [Line Items]
Other commitments, unfunded amount	$ 3.0
Lagunita Biosciences, LLC | Commitment to Invest
Other Commitments [Line Items]
Term of capital commitment	3 years
Eclipse Fund II, L.P. [Member]
Other Commitments [Line Items]
Other commitments, unfunded amount	$ 0.9
Eclipse Fund II, L.P. [Member] | Commitment to Invest
Other Commitments [Line Items]
Term of capital commitment	8 years
Eclipse Continuity Fund I, L.P. [Member]
Other Commitments [Line Items]
Other commitments, unfunded amount	$ 0.9
Eclipse Continuity Fund I, L.P. [Member] | Commitment to Invest
Other Commitments [Line Items]
Term of capital commitment	9 years

[1] five real estate investments held by the Company, all of which pertain to related party investments. Such commitments can be called at any time up to

[2] The Company is a limited partner of the HealthCare Royalty Partners funds (which are managed by Healthcare Royalty Management) and is a member of HealthCare Royalty Partners General Partners. The Company will make its pro-rata investment in the HealthCare Royalty Partners funds along with the other limited partners.