Investments - Additional Information (Details) - USD ($)	3 Months Ended			9 Months Ended
	Sep. 30, 2017	Jun. 30, 2017	Sep. 30, 2016	Sep. 30, 2017	Sep. 30, 2016	Dec. 31, 2016	Dec. 31, 2010
Schedule of Investments [Line Items]
Marketable Securities and Certificates of Deposit	$ 115,752,000			$ 115,752,000		$ 66,487,000
Net Realized and Unrealized Gains (Losses) on Private Equity Fund Investments, Including Performance Fees	1,208,000		$ 171,000	(985,000)	$ 6,302,000
Previously Received Carried Interest Subject to Repayment	0			0
Variable Interest Entity, Nonconsolidated, Carrying Amount, Assets	10,696,000			10,696,000		9,889,000
Variable Interest Entity, Reporting Entity Involvement, Maximum Loss Exposure, Amount	13,035,000			13,035,000
Unfunded Commitments for Capital Contributions	3,529,000			3,529,000
Cost Method Investments	1,079,000			1,079,000		1,079,000
Income (Loss) from Equity Method Investments	1,827,000		1,178,000	5,507,000	4,129,000
Investment Banking [Member]
Schedule of Investments [Line Items]
Income (Loss) from Equity Method Investments	(75,000)		(112,000)	(111,000)	(94,000)
Amortization of Intangible Assets	2,357,000		2,582,000	7,071,000	8,659,000
Trilantic [Member]
Schedule of Investments [Line Items]
Issued LP Units (in shares)							500,000
Limited Partnership Investment							$ 16,090,000
Participation in Successor Funds	12,000,000			12,000,000
Glisco [Member]
Schedule of Investments [Line Items]
Cost Method Investments	$ 2,172,000			$ 2,172,000		2,463,000
G5 Evercore [Member]
Schedule of Investments [Line Items]
Equity Method Investment, Ownership Percentage	49.00%			49.00%
Income (Loss) from Equity Method Investments	$ (93,000)		(107,000)	$ (144,000)	(78,000)
G5 Evercore [Member] | Special Charges [Member] | Investment Banking [Member]
Schedule of Investments [Line Items]
Equity Method Investment, Other than Temporary Impairment		$ 14,400,000		$ 14,400,000
ABS [Member]
Schedule of Investments [Line Items]
Equity Method Investment, Ownership Percentage	45.00%			45.00%
Income (Loss) from Equity Method Investments	$ 1,676,000		1,113,000	$ 4,919,000	3,687,000
Atalanta Sosnoff [Member]
Schedule of Investments [Line Items]
Equity Method Investment, Ownership Percentage	49.00%			49.00%
Income (Loss) from Equity Method Investments	$ 190,000		172,000	$ 621,000	520,000
Luminis [Member]
Schedule of Investments [Line Items]
Equity Method Investment, Ownership Percentage	19.00%			19.00%
Income (Loss) from Equity Method Investments	$ 54,000			$ 111,000
Variable Interest Entity, Not Primary Beneficiary [Member] | Minimum [Member] | ECP II [Member]
Schedule of Investments [Line Items]
Percent Ownership of Carried Interest				8.00%
Variable Interest Entity, Not Primary Beneficiary [Member] | Maximum [Member] | ECP II [Member]
Schedule of Investments [Line Items]
Percent Ownership of Carried Interest				9.00%
Trilantic [Member]
Schedule of Investments [Line Items]
Investment	10,462,000			$ 10,462,000		11,632,000
Trilantic [Member] | Trilantic V [Member]
Schedule of Investments [Line Items]
Investment	1,170,000			1,170,000		3,280,000
Capital Commitment	5,000,000			5,000,000
Unfunded Commitments for Capital Contributions	1,130,000			1,130,000
Trilantic [Member] | Trilantic IV [Member]
Schedule of Investments [Line Items]
Investment						1,178,000
Equity Method Investments [Member]
Schedule of Investments [Line Items]
Amortization of Intangible Assets	391,000		$ 884,000	1,172,000	$ 2,648,000
Private Equity Funds [Member]
Schedule of Investments [Line Items]
Equity Method Investment	15,776,000			15,776,000		21,742,000
Private Equity Funds [Member] | ECP II [Member]
Schedule of Investments [Line Items]
Equity Method Investment	838,000			838,000		$ 933,000
Cash	814,000			814,000
Marketable Securities and Certificates of Deposit	$ 24,000			$ 24,000