Investments of Operating Entities and Consolidated Funds - Portfolio Funds (Details) (USD $) In Thousands, unless otherwise specified	12 Months Ended
	Dec. 31, 2014		Dec. 31, 2013
Investment Holdings [Line Items]
Portfolio Funds, Consolidated Funds	$ 188,884		$ 182,638
Other investments	167,464		99,483
Enterprise LP
Investment Holdings [Line Items]
Portfolio Funds, Consolidated Funds	138,253		155,530
Merger Fund
Investment Holdings [Line Items]
Portfolio Funds, Consolidated Funds	50,631		26,963
Consolidated Fund of Funds
Investment Holdings [Line Items]
Portfolio Funds, Consolidated Funds	0		145
Portfolio Funds
Investment Holdings [Line Items]
Other investments	103,466		71,051
Portfolio Funds | Healthcare Royalty Partners | Affiliated Entity
Investment Holdings [Line Items]
Other investments	11,935	[1],[2]	9,741	[1],[2]
Portfolio Funds | Healthcare Royalty Partners II | Affiliated Entity
Investment Holdings [Line Items]
Other investments	6,648	[1],[2]	4,961	[1],[2]
Portfolio Funds | Orchard Square Partners Credit Fund LP | Affiliated Entity
Investment Holdings [Line Items]
Other investments	11,532	[3]	12,674	[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	21,792	[2],[4]	17,495	[2],[4]
Required notice period, withdrawal	90 days		90 days
Portfolio Funds | Starboard Partners Fund LP | Affiliated Entity
Investment Holdings [Line Items]
Other investments	14,652	[2],[5]	0	[2],[5]
Portfolio Funds | Starboard Leaders Fund LP | Affiliated Entity
Investment Holdings [Line Items]
Other investments	1,367	[2],[6]	552	[2],[6]
Portfolio Funds | Formation 8 Partners Fund I LP
Investment Holdings [Line Items]
Other investments	11,283	[7]	2,788	[7]
Portfolio Funds | RCG LV Park Lane LLC | Affiliated Entity
Investment Holdings [Line Items]
Other investments	642	[2],[8]	678	[2],[8]
Portfolio Funds | RCGL 12E13th LLC | Affiliated Entity
Investment Holdings [Line Items]
Other investments	638	[2],[9]	558	[2],[9]
Portfolio Funds | RCGLongview Debt Fund V, L.P. | Affiliated Entity
Investment Holdings [Line Items]
Other investments	12,876	[2],[9]	11,979	[2],[9]
Portfolio Funds | Other Funds
Investment Holdings [Line Items]
Other investments	7,324	[10]	7,772	[10]
Portfolio Funds | Other Funds | Affiliated Entity
Investment Holdings [Line Items]
Other investments	2,777	[11],[2]	1,853	[11],[2]
Portfolio Funds | Enterprise Master
Investment Holdings [Line Items]
Other investments	135,846		144,223
Portfolio Funds | Enterprise Master | RCG Longview Equity Fund, LP | Affiliated Entity | Real Estate Strategy
Investment Holdings [Line Items]
Other investments	9,090	[12]	8,470	[12]
Portfolio Funds | Enterprise Master | RCG Longview II, LP | Affiliated Entity | Real Estate Strategy
Investment Holdings [Line Items]
Other investments	747	[12]	800	[12]
Portfolio Funds | Enterprise Master | RCG Longview Debt Fund IV, LP | Affiliated Entity | Real Estate Strategy
Investment Holdings [Line Items]
Other investments	5,348	[12]	17,641	[12]
Portfolio Funds | Enterprise Master | RCG Longview, LP | Affiliated Entity | Real Estate Strategy
Investment Holdings [Line Items]
Other investments	40	[12]	319	[12]
Portfolio Funds | Enterprise Master | RCG Soundview, LLC | Affiliated Entity | Real Estate Strategy
Investment Holdings [Line Items]
Other investments	452	[12]	442	[12]
Portfolio Funds | Enterprise Master | RCG Urban American Real Estate Fund, L.P. | Affiliated Entity | Real Estate Strategy
Investment Holdings [Line Items]
Other investments	1,161	[12]	1,812	[12]
Portfolio Funds | Enterprise Master | RCG International Sarl | Affiliated Entity | Multi-strategy
Investment Holdings [Line Items]
Other investments	2,113	[12]	1,795	[12]
Portfolio Funds | Enterprise Master | RCG Special Opportunities Fund, Ltd | Affiliated Entity | Multi-strategy
Investment Holdings [Line Items]
Other investments	92,405	[12]	82,119	[12]
Portfolio Funds | Enterprise Master | RCG Endeavour, LLC | Affiliated Entity | Multi-strategy
Investment Holdings [Line Items]
Other investments	0	[12]	6	[12]
Portfolio Funds | Enterprise Master | RCG Energy, LLC | Affiliated Entity | Energy Strategy
Investment Holdings [Line Items]
Other investments	2,294	[12]	2,842	[12]
Portfolio Funds | Enterprise Master | RCG Renergys, LLC | Affiliated Entity | Energy Strategy
Investment Holdings [Line Items]
Other investments	1	[12]	1	[12]
Portfolio Funds | Enterprise Master | Other Private Investment | Various Strategies
Investment Holdings [Line Items]
Other investments	12,057		12,952
Portfolio Funds | Enterprise Master | Real Estate Funds | Real Estate Strategy
Investment Holdings [Line Items]
Other investments	$ 10,138	[12]	$ 15,024	[12]

[1] 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.

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

[3] Orchard Square Partners 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] Starboard Partners Fund LP permits redemptions on a semi-annual basis on 180 days prior written notice subsequent to an initial two year period when redemptions are not permitted.

[6] Starboard Leaders Fund LP does not permit withdrawals, but instead allows terminations with respect to capital commitments upon 30 days prior written notice at any time following the first anniversary of an investors initial capital contribution.

[7] 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.

[8] 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.

[9] 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.

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

[11] 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.

[12] Affiliates of the Company.