Investments - Additional Information (Details) - USD ($)	3 Months Ended
	Mar. 31, 2017	Mar. 31, 2016	Dec. 31, 2016	Dec. 31, 2015	Dec. 31, 2010
Schedule of Investments [Line Items]
Marketable Securities	$ 62,829,000		$ 66,487,000
Net Realized and Unrealized Gains (Losses) on Private Equity Fund Investments, Including Performance Fees	339,000	$ 1,367,000
Previously Received Carried Interest Subject to Repayment	0
Variable Interest Entity, Nonconsolidated, Carrying Amount, Assets	9,743,000
Variable Interest Entity, Reporting Entity Involvement, Maximum Loss Exposure, Amount	12,086,000
Unfunded Commitments for Capital Contributions	4,392,000
Cost Method Investments				$ 1,079,000
Income (Loss) from Equity Method Investments	1,610,000	1,287,000
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
Glisco [Member]
Schedule of Investments [Line Items]
Cost Method Investments	$ 2,317,000		2,463,000
G5 Evercore [Member]
Schedule of Investments [Line Items]
Equity Method Investment, Ownership Percentage	49.00%
Income (Loss) from Equity Method Investments	$ (26,000)	(248,000)
ABS [Member]
Schedule of Investments [Line Items]
Equity Method Investment, Ownership Percentage	45.00%
Income (Loss) from Equity Method Investments	$ 1,531,000	1,330,000
Atalanta Sosnoff [Member]
Schedule of Investments [Line Items]
Equity Method Investment, Ownership Percentage	49.00%
Income (Loss) from Equity Method Investments	$ 105,000	205,000
Luminis [Member]
Schedule of Investments [Line Items]
Equity Method Investment, Ownership Percentage	19.00%
Minimum [Member] | ECP II [Member] | Variable Interest Entity, Not Primary Beneficiary [Member]
Schedule of Investments [Line Items]
Percent Ownership of Carried Interest	8.00%
Maximum [Member] | ECP II [Member] | Variable Interest Entity, Not Primary Beneficiary [Member]
Schedule of Investments [Line Items]
Percent Ownership of Carried Interest	9.00%
Trilantic [Member]
Schedule of Investments [Line Items]
Investment	$ 11,512,000		11,632,000
Trilantic [Member] | Trilantic V [Member]
Schedule of Investments [Line Items]
Investment	120,000		3,280,000
Capital Commitment	5,000,000
Unfunded Commitments for Capital Contributions	1,989,000
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	390,000	$ 880,000
Private Equity Funds [Member]
Schedule of Investments [Line Items]
Equity Method Investment	13,855,000		21,742,000
Private Equity Funds [Member] | ECP II [Member]
Schedule of Investments [Line Items]
Equity Method Investment	933,000		$ 933,000
Cash	852,000
Marketable Securities	$ 81,000