Commitments and Contingencies (Details) (USD $)	3 Months Ended												3 Months Ended			1 Months Ended			3 Months Ended
	Mar. 31, 2013	Mar. 31, 2012	Dec. 31, 2011	Mar. 31, 2013 Equipment Leases		Mar. 31, 2013 Service Payments	Mar. 31, 2013 Facility Leases		Mar. 31, 2013 Buildings, Avenue of Americas	Dec. 31, 2012 Buildings, Avenue of Americas	Mar. 31, 2013 Clawback Obligation	Mar. 31, 2013 Unfunded Commitments investments	Mar. 31, 2013 Commitment to Invest Healthcare Royalty Partners Affiliated Entity	Mar. 31, 2013 Commitment to Invest Healthcare Royalty Partners Affiliated Entity Minimum	Mar. 31, 2013 Commitment to Invest Healthcare Royalty Partners Affiliated Entity Maximum	Apr. 30, 2011 Commitment to Invest Starboard Value L.P. Affiliated Entity	Jan. 31, 2013 Commitment to Invest OSP Credit Fund LP (formerly known as Ramius Global Credit Fund LP ) [Member] Affiliated Entity	Sep. 30, 2012 Commitment to Invest Formation 8 Partners Fund I Affiliated Entity	Mar. 31, 2013 Commitment to Invest Formation 8 Partners Fund I Affiliated Entity
Lease Obligations
Net rent expense	$ 3,700,000	$ 3,700,000
Future Rent Payments Liability			5,700,000
Liability relating to vacating premises									1,600,000	2,800,000
Future minimum annual lease and service payments
2013				2,476,000	[1]	10,272,000	15,862,000	[2]
2014				1,548,000	[1]	9,325,000	19,212,000	[2]
2015				1,051,000	[1]	2,166,000	16,152,000	[2]
2016				194,000	[1]	189,000	13,039,000	[2]
2017				0	[1]	0	9,938,000	[2]
Thereafter				0	[1]	0	43,733,000	[2]
Future minimum annual lease and service payments				5,269,000	[1]	21,952,000	117,936,000	[2]
Sublease income related to operating leases	300,000	500,000
Contractual obligation											6,200,000	8,100,000	42,200,000
Number of real estate investments, in investments												3
Expected call period														2 years	5 years
Funding toward commitments													27,700,000						1,500,000
Commitments made																$ 15,000,000.0	$ 10,000,000.0	$ 10,000,000.0
Term of capital commitment																			5 years

[1] Equipment Leases include the Company's commitments relating to operating and capital leases. See Note 14 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 $0.3 million and $0.5 million for the three months ended March 31, 2013 and 2012, respectively.