Investments - Additional Information (Details) - USD ($)	3 Months Ended		9 Months Ended
	Sep. 30, 2020	Sep. 30, 2019	Sep. 30, 2020	Sep. 30, 2019	Dec. 31, 2019	Dec. 31, 2010
Schedule of Investments [Line Items]
Income from Equity Method Investments	$ 3,111,000	$ 2,562,000	$ 8,552,000	$ 7,226,000
Net Realized and Unrealized Gains (Losses) on Private Equity Fund Investments, Including Performance Fees	697,000	(49,000)	(1,646,000)	(176,000)
Previously Received Carried Interest Subject to Repayment	347,000		347,000
Variable Interest Entity, Nonconsolidated, Carrying Amount, Assets	2,975,000		2,975,000		$ 4,658,000
Variable Interest Entity, Reporting Entity Involvement, Maximum Loss Exposure, Amount	5,483,000		5,483,000		8,810,000
Unfunded Commitments for Capital Contributions	11,998,000		11,998,000
Equity Method Investments [Member]
Schedule of Investments [Line Items]
Amortization of Intangible Assets	$ 79,000	171,000	$ 237,000	513,000
ABS [Member]
Schedule of Investments [Line Items]
Equity Method Investment, Ownership Percentage	46.00%		46.00%
Income from Equity Method Investments	$ 1,917,000	1,936,000	$ 5,740,000	5,588,000
Atalanta Sosnoff [Member]
Schedule of Investments [Line Items]
Equity Method Investment, Ownership Percentage	49.00%		49.00%
Income from Equity Method Investments	$ 624,000	344,000	$ 1,641,000	882,000
Luminis [Member]
Schedule of Investments [Line Items]
Equity Method Investment, Ownership Percentage	20.00%		20.00%
Income from Equity Method Investments	$ 570,000	282,000	$ 1,171,000	756,000
G5 [Member]
Schedule of Investments [Line Items]
Debt Securities, Held-to-maturity	6,684,000		6,684,000		9,235,000
Trilantic [Member]
Schedule of Investments [Line Items]
Issued LP Units (in shares)						500,000
Limited Partnership Investment						$ 16,090,000
Investment	6,638,000		6,638,000		6,762,000
Trilantic IV [Member]
Schedule of Investments [Line Items]
Investment					1,178,000
Trilantic V [Member]
Schedule of Investments [Line Items]
Investment	14,000		14,000		5,135,000
Capital Commitment	5,000,000		5,000,000
Unfunded Commitments for Capital Contributions	376,000		376,000
Trilantic VI [Member]
Schedule of Investments [Line Items]
Investment	110,000		110,000		3,015,000
Capital Commitment	12,000,000		12,000,000
Unfunded Commitments for Capital Contributions	9,054,000		9,054,000
Other Ownership Interests, Contributed Capital		$ 3,015,000		$ 3,015,000
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	645,000		645,000		693,000
Glisco [Member]
Schedule of Investments [Line Items]
Equity Securities without Readily Determinable Fair Value, Amount	$ 387,000		$ 387,000		$ 899,000