Investments - Additional Information (Details) - USD ($)	3 Months Ended		6 Months Ended
	Jun. 30, 2019	Jun. 30, 2018	Jun. 30, 2019	Jun. 30, 2018	Dec. 31, 2018	Dec. 31, 2010
Schedule of Investments [Line Items]
Income from Equity Method Investments	$ 2,453,000	$ 2,419,000	$ 4,664,000	$ 4,544,000
Equity Method Investment	54,506,000		54,506,000		$ 58,507,000
Net Realized and Unrealized Gains (Losses) on Private Equity Fund Investments, Including Performance Fees	(123,000)	(204,000)	(127,000)	142,000
Previously Received Carried Interest Subject to Repayment	0		0
Variable Interest Entity, Nonconsolidated, Carrying Amount, Assets	5,108,000		5,108,000		5,445,000
Variable Interest Entity, Reporting Entity Involvement, Maximum Loss Exposure, Amount	7,672,000		7,672,000		8,048,000
Unfunded Commitments for Capital Contributions	12,418,000		12,418,000
Equity Method Investments [Member]
Schedule of Investments [Line Items]
Amortization of Intangible Assets	171,000	223,000	342,000	445,000
Private Equity Funds [Member]
Schedule of Investments [Line Items]
Equity Method Investment	15,096,000		15,096,000		9,800,000
2015 Private Company Securities [Member]
Schedule of Investments [Line Items]
Equity Securities without Readily Determinable Fair Value, Amount	1,079,000		1,079,000		1,079,000
2019 Private Company Securities [Member]
Schedule of Investments [Line Items]
Equity Securities without Readily Determinable Fair Value, Amount	$ 934,000		$ 934,000
ABS [Member]
Schedule of Investments [Line Items]
Equity Method Investment, Ownership Percentage	46.00%		46.00%
Income from Equity Method Investments	$ 1,921,000	1,891,000	$ 3,652,000	3,763,000
Equity Method Investment	$ 36,172,000		$ 36,172,000		38,699,000
Atalanta Sosnoff [Member]
Schedule of Investments [Line Items]
Equity Method Investment, Ownership Percentage	49.00%		49.00%
Income from Equity Method Investments	$ 313,000	231,000	$ 538,000	484,000
Equity Method Investment	$ 12,726,000		$ 12,726,000		13,291,000
Luminis [Member]
Schedule of Investments [Line Items]
Equity Method Investment, Ownership Percentage	20.00%		20.00%
Income from Equity Method Investments	$ 219,000	$ 297,000	$ 474,000	$ 297,000
Equity Method Investment	5,608,000		5,608,000		6,517,000
G5 [Member]
Schedule of Investments [Line Items]
Debt Securities, Held-to-maturity	9,509,000		9,509,000		9,717,000
Trilantic VI [Member]
Schedule of Investments [Line Items]
Other Ownership Interests, Contributed Capital	2,642,000		2,642,000
Investment	2,642,000		2,642,000
Capital Commitment	12,000,000		12,000,000
Unfunded Commitments for Capital Contributions	9,358,000		$ 9,358,000
ECP II [Member] | Variable Interest Entity, Not Primary Beneficiary [Member] | Minimum [Member]
Schedule of Investments [Line Items]
Percent Ownership of Carried Interest			8.00%
ECP II [Member] | Variable Interest Entity, Not Primary Beneficiary [Member] | Maximum [Member]
Schedule of Investments [Line Items]
Percent Ownership of Carried Interest			9.00%
ECP II [Member] | Private Equity Funds [Member]
Schedule of Investments [Line Items]
Equity Method Investment	765,000		$ 765,000		795,000
Trilantic IV [Member]
Schedule of Investments [Line Items]
Investment					1,178,000
Trilantic V [Member]
Schedule of Investments [Line Items]
Investment	147,000		147,000		4,980,000
Capital Commitment	5,000,000		5,000,000
Unfunded Commitments for Capital Contributions	436,000		436,000
Trilantic [Member]
Schedule of Investments [Line Items]
Issued LP Units (in shares)						500,000
Limited Partnership Investment						$ 16,090,000
Investment	7,143,000		7,143,000		9,932,000
Glisco [Member]
Schedule of Investments [Line Items]
Equity Securities without Readily Determinable Fair Value, Amount	$ 1,253,000		$ 1,253,000		$ 1,609,000