Commitments and Contingencies (Details) (USD $)	3 Months Ended		9 Months Ended											9 Months Ended			1 Months Ended
	Sep. 30, 2012	Sep. 30, 2011	Sep. 30, 2012	Sep. 30, 2011	Sep. 30, 2012 Equipment Leases [Member]		Sep. 30, 2012 Service Payments [Member]	Sep. 30, 2012 Facility Leases [Member]		Sep. 30, 2012 Buildings, Avenue of Americas [Member]	Dec. 31, 2011 Buildings, Avenue of Americas [Member]	Sep. 30, 2012 Clawback Obligation [Member]	Sep. 30, 2012 Unfunded Commitments [Member] investments	Sep. 30, 2012 Commitment to Invest [Member] Cowen Healthcare Royalty Partners [Member] Affiliated Entity [Member]	Sep. 30, 2011 Commitment to Invest [Member] Cowen Healthcare Royalty Partners [Member] Affiliated Entity [Member] Minimum [Member]	Sep. 30, 2011 Commitment to Invest [Member] Cowen Healthcare Royalty Partners [Member] Affiliated Entity [Member] Maximum [Member]	Apr. 30, 2011 Commitment to Invest [Member] Starboard Value L.P. [Member] Affiliated Entity [Member]	Sep. 30, 2012 Unfunded Commitment to Invest [Member] Starboard Value L.P. [Member] Affiliated Entity [Member]
Lease Obligations
Net rent expense	$ 3,600,000	$ 3,600,000	$ 11,000,000	$ 10,500,000
Liability relating to vacating premises										3,300,000	5,700,000
Future minimum annual lease and service payments
2012					825,000	[1]	2,445,000	4,503,000	[2]
2013					3,301,000	[1]	10,920,000	17,560,000	[2]
2014					1,548,000	[1]	7,935,000	15,396,000	[2]
2015					1,051,000	[1]	2,030,000	12,310,000	[2]
2016					194,000	[1]	194,000	11,421,000	[2]
Thereafter					0	[1]	0	53,607,000	[2]
Future minimum annual lease and service payments					6,919,000	[1]	23,524,000	114,797,000	[2]
Sublease income related to operating leases	300,000	100,000	1,000,000	300,000
Contractual obligation												6,200,000	6,400,000	42,200,000				2,900,000
Number of real estate investments, in investments													2
Funding toward commitments														26,300,000
Commitments made																	$ 15,000,000
Expected call period															2 years	5 years

[1] Equipment Leases include the Company's commitments relating to operating and capital leases. See Note 15 for further information on capital lease minimum payments.

[2] The Company has entered into various agreements to sublease certain of its premises. The Company recorded sublease income related to these leases of $0.3 million and $0.1 million for the three months ended September 30, 2012 and 2011, respectively, and $1.0 million and $0.3 million for the nine months ended September 30, 2012 and 2011