Commitments and Contingencies (Details) (USD $)	12 Months Ended												12 Months Ended				12 Months Ended			1 Months Ended	12 Months Ended
	Dec. 31, 2013	Dec. 31, 2012	Dec. 31, 2011	Dec. 31, 2013 Equipment Leases		Dec. 31, 2013 Service Payments	Dec. 31, 2013 Facility Leases		Dec. 31, 2012 Buildings, Avenue of Americas	Dec. 31, 2011 Buildings, Avenue of Americas	Dec. 31, 2013 Clawback Obligation [Member]	Dec. 31, 2012 Clawback Obligation [Member]	Dec. 31, 2013 Commitment to Invest Healthcare Royalty Partners Affiliated Entity	Dec. 31, 2013 Commitment to Invest Healthcare Royalty Partners Affiliated Entity Minimum	Dec. 31, 2013 Commitment to Invest Healthcare Royalty Partners Affiliated Entity Maximum	Apr. 30, 2011 Commitment to Invest Starboard Value and Opportunity Fund LP Affiliated Entity	Dec. 31, 2013 Commitment to Invest Starboard Leaders Fund LP Affiliated Entity	Apr. 30, 2013 Commitment to Invest Starboard Leaders Fund LP Affiliated Entity	Jan. 31, 2013 Commitment to Invest Orchard Square Partners Credit Fund LP Affiliated Entity	Sep. 30, 2012 Commitment to Invest Formation 8 Partners Fund I LP Affiliated Entity	Dec. 31, 2013 Commitment to Invest Formation 8 Partners Fund I LP Affiliated Entity	Dec. 31, 2013 Unfunded Commitments cowenfund	Dec. 31, 2013 Unfunded Commitments Affiliated Entity
Lease Obligations
Net rent expense	$ 15,600,000	$ 14,300,000	$ 16,700,000
Future Rent Payments Liability										5,700,000
Liability relating to vacating premises									2,800,000
Future minimum annual lease and service payments
Contractual Obligation, Due in Next Twelve Months				810,000	[1]	11,970,000	17,862,000	[2]
Contractual Obligation, Due in Second Year				405,000	[1]	5,499,000	17,375,000	[2]
Contractual Obligation, Due in Third Year				86,000	[1]	1,634,000	14,283,000	[2]
Contractual Obligation, Due in Fourth Year				0	[1]	1,133,000	11,174,000	[2]
Contractual Obligation, Due in Fifth Year				0	[1]	1,049,000	10,885,000	[2]
Contractual Obligation, Due after Fifth Year				0	[1]	22,000	39,594,000	[2]
Future minimum annual lease and service payments				1,301,000	[1]	21,307,000	111,173,000	[2]
Sublease income related to operating leases	1,500,000	1,200,000	300,000
Contractual obligation											6,200,000	6,200,000	42,400,000			15,000,000		1,000,000	10,000,000				13,200,000
Number of real estate investments, in investments																						4
Expected call period														2 years	5 years
Funding toward commitments													29,900,000				500,000				3,000,000
Commitments made																				$ 10,000,000
Term of capital commitment																					5 years

[1] Equipment Leases include the Company's commitments relating to operating and capital leases. See Note 20 for further information on the capital lease minimum payments which are included in the table

[2] The Company has entered into various agreements to sublease certain of its premises. The Company recorded sublease income related to these leases of $1.5 million, $1.2 million, and $0.3 million for the years ended December 31, 2013, 2012, and 2011, respectively.