Investments of Operating Entities and Consolidated Funds - Portfolio Funds (Details) (USD $) In Thousands, unless otherwise specified	6 Months Ended
	Jun. 30, 2014		Jun. 30, 2013	Dec. 31, 2013
Investment Holdings [Line Items]
Portfolio Funds, Consolidated Funds	$ 194,474			$ 182,638
Other investments	114,551			99,483
Enterprise LP
Investment Holdings [Line Items]
Portfolio Funds, Consolidated Funds	145,371			155,530
Merger Fund
Investment Holdings [Line Items]
Portfolio Funds, Consolidated Funds	49,103			26,963
Consolidated Fund of Funds [Member]
Investment Holdings [Line Items]
Portfolio Funds, Consolidated Funds	0			145
Portfolio Funds
Investment Holdings [Line Items]
Other investments	83,967			71,051
Portfolio Funds | Healthcare Royalty Partners | Affiliated Entity
Investment Holdings [Line Items]
Other investments	10,947	[1],[2]		9,741	[1],[2]
Portfolio Funds | Healthcare Royalty Partners II | Affiliated Entity
Investment Holdings [Line Items]
Other investments	6,578	[1],[2]		4,961	[1],[2]
Portfolio Funds | Orchard Square Partners Credit Fund LP | Affiliated Entity
Investment Holdings [Line Items]
Other investments	14,093	[1],[3]		12,674	[1],[3]
Required notice period, redemption	60 days		60 days
Penalty on redemptions of less than one year	4.00%		4.00%
Portfolio Funds | Starboard Value and Opportunity Fund LP | Affiliated Entity
Investment Holdings [Line Items]
Other investments	18,888	[1],[4]		17,495	[1],[4]
Required notice period, withdrawal	90 days		90 days
Portfolio Funds | Formation 8 Partners Fund I LP
Investment Holdings [Line Items]
Other investments	6,962	[5]		2,788	[5]
Portfolio Funds | RCG LV Park Lane LLC
Investment Holdings [Line Items]
Other investments	707	[6]		678	[6]
Portfolio Funds | RCGL 12E13th LLC
Investment Holdings [Line Items]
Other investments	611	[7]		558	[7]
Portfolio Funds | RCGLongview Debt Fund V, L.P.
Investment Holdings [Line Items]
Other investments	14,560	[7]		11,979	[7]
Portfolio Funds | Other Funds
Investment Holdings [Line Items]
Other investments	7,737	[8]		7,772	[8]
Portfolio Funds | Other Funds | Affiliated Entity
Investment Holdings [Line Items]
Other investments	2,884	[1],[9]		2,405	[1],[9]
Portfolio Funds | Enterprise Master
Investment Holdings [Line Items]
Other investments	141,338			144,223
Portfolio Funds | Enterprise Master | RCG Longview Equity Fund, LP | Affiliated Entity | Real Estate Strategy
Investment Holdings [Line Items]
Other investments	9,031	[10]		8,470	[10]
Portfolio Funds | Enterprise Master | RCG Longview II, LP | Affiliated Entity | Real Estate Strategy
Investment Holdings [Line Items]
Other investments	760	[10]		800	[10]
Portfolio Funds | Enterprise Master | RCG Longview Debt Fund IV, LP | Affiliated Entity | Real Estate Strategy
Investment Holdings [Line Items]
Other investments	9,360	[10]		17,641	[10]
Portfolio Funds | Enterprise Master | RCG Longview, LP | Affiliated Entity | Real Estate Strategy
Investment Holdings [Line Items]
Other investments	423	[10]		319	[10]
Portfolio Funds | Enterprise Master | RCG Soundview, LLC | Affiliated Entity | Real Estate Strategy
Investment Holdings [Line Items]
Other investments	442	[10]		442	[10]
Portfolio Funds | Enterprise Master | RCG Urban American Real Estate Fund, L.P. | Affiliated Entity | Real Estate Strategy
Investment Holdings [Line Items]
Other investments	1,128	[10]		1,812	[10]
Portfolio Funds | Enterprise Master | RCG International Sarl | Affiliated Entity | Multi-strategy
Investment Holdings [Line Items]
Other investments	1,643	[10]		1,795	[10]
Portfolio Funds | Enterprise Master | RCG Special Opportunities Fund, Ltd | Affiliated Entity | Multi-strategy
Investment Holdings [Line Items]
Other investments	85,924	[10]		82,119	[10]
Portfolio Funds | Enterprise Master | RCG Endeavour, LLC | Affiliated Entity | Multi-strategy
Investment Holdings [Line Items]
Other investments	4	[10]		6	[10]
Portfolio Funds | Enterprise Master | RCG Energy, LLC | Affiliated Entity | Energy Strategy
Investment Holdings [Line Items]
Other investments	3,281	[10]		2,842	[10]
Portfolio Funds | Enterprise Master | RCG Renergys, LLC | Affiliated Entity | Energy Strategy
Investment Holdings [Line Items]
Other investments	1	[10]		1	[10]
Portfolio Funds | Enterprise Master | Other Private Investment | Various Strategies
Investment Holdings [Line Items]
Other investments	13,113			12,952
Portfolio Funds | Enterprise Master | Real Estate Funds | Real Estate Strategy
Investment Holdings [Line Items]
Other investments	$ 16,228			$ 15,024

[1] These portfolio funds are affiliates of the Company.

[2] HealthCare Royalty Partners, L.P. and HealthCare Royalty Partners II, L.P. are private equity funds and therefore distributions will be made when cash flows are received from the underlying investments, typically on a quarterly basis.

[3] Orchard Square Partners Credit Fund LP (formerly known as Ramius Global Credit Fund LP) has a quarterly redemption policy with a 60 day notice period and a 4% penalty on redemptions of investments of less than a year in duration.

[4] Starboard Value and Opportunity Fund LP permits quarterly withdrawals upon 90 days notice.

[5] Formation 8 Partners Fund I is a private equity fund which invests in equity of early stage and growth transformational information and energy technology companies. Distributions will be made when the underlying investments are liquidated.

[6] RCG LV Park Lane LLC is a single purpose entity formed to participate in a joint venture which acquired, at a discount, the mortgage notes on a portfolio of multifamily real estate properties located in Birmingham, Alabama. RCG LV Park Lane LLC is a private equity structure and therefore distributions will be made when the underlying investments are liquidated.

[7] RCGL 12E13th LLC and RCG Longview Debt Fund V, L.P. are real estate private equity structures and therefore distributions will be made when the underlying investments are liquidated.

[8] Other private investment represents the Company's closed end investment in a portfolio fund that invests in a wireless broadband communication provider in Italy.

[9] The majority of these funds are affiliates of the Company or are managed by the Company and the investors can redeem from these funds as investments are liquidated.

[10] Affiliates of the Company.