Investments - Additional Information (Details) - USD ($)	3 Months Ended								12 Months Ended
	Dec. 31, 2019	Sep. 30, 2019	Jun. 30, 2019	Mar. 31, 2019	Dec. 31, 2018	Sep. 30, 2018	Jun. 30, 2018	Mar. 31, 2018	Dec. 31, 2019	Dec. 31, 2018	Dec. 31, 2017	May 31, 2017	Dec. 31, 2010
Schedule of Investments [Line Items]
Income from Equity Method Investments	$ 3,770,000	$ 2,562,000	$ 2,453,000	$ 2,211,000	$ 2,452,000	$ 2,298,000	$ 2,419,000	$ 2,125,000	$ 10,996,000	$ 9,294,000	$ 8,838,000
Equity Method Investment	57,275,000				58,507,000				57,275,000	58,507,000
Amortization of Intangible Assets									8,077,000	9,199,000	9,793,000
Net Realized and Unrealized Gains (Losses) on Private Equity Fund Investments, Including Performance Fees									(790,000)	(397,000)	(915,000)
Previously Received Carried Interest Subject to Repayment	0								0
Variable Interest Entity, Nonconsolidated, Carrying Amount, Assets	4,658,000				5,445,000				4,658,000	5,445,000
Variable Interest Entity, Reporting Entity Involvement, Maximum Loss Exposure, Amount	8,810,000				8,048,000				8,810,000	8,048,000
Unfunded Commitments for Capital Contributions	13,767,000								13,767,000
Equity Method Investments [Member]
Schedule of Investments [Line Items]
Amortization of Intangible Assets									684,000	893,000	1,505,000
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	1,079,000
2019 Private Company Securities [Member]
Schedule of Investments [Line Items]
Equity Securities without Readily Determinable Fair Value, Amount	$ 693,000								693,000
Investment Banking [Member]
Schedule of Investments [Line Items]
Income from Equity Method Investments									$ 916,000	518,000	277,000
ABS [Member]
Schedule of Investments [Line Items]
Equity Method Investment, Ownership Percentage	46.00%								46.00%
Income from Equity Method Investments									$ 8,870,000	7,565,000	7,990,000
Equity Method Investment	$ 40,052,000				38,699,000				$ 40,052,000	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									$ 1,210,000	1,211,000	493,000
Equity Method Investment	$ 12,300,000				13,291,000				$ 12,300,000	13,291,000
Luminis [Member]
Schedule of Investments [Line Items]
Equity Method Investment, Ownership Percentage	20.00%								20.00%
Income from Equity Method Investments									$ 916,000	518,000	499,000
Equity Method Investment	$ 4,923,000				6,517,000				4,923,000	6,517,000
G5 [Member]
Schedule of Investments [Line Items]
Income from Equity Method Investments											(144,000)
Equity Method Investment												$ 11,555,000
Debt Securities, Held-to-maturity	9,235,000				9,717,000				9,235,000	9,717,000
G5 [Member] | Special Charges [Member] | Investment Banking [Member]
Schedule of Investments [Line Items]
Equity Method Investment, Other than Temporary Impairment											$ 14,400,000
Trilantic VI [Member]
Schedule of Investments [Line Items]
Investment	3,015,000								3,015,000
Capital Commitment	12,000,000								12,000,000
Unfunded Commitments for Capital Contributions	9,164,000								9,164,000
Other Ownership Interests, Contributed Capital	2,836,000								2,836,000
Glisco II [Member]
Schedule of Investments [Line Items]
Distribution Made to Limited Partner, Cash Distributions Paid										2,059,000
Trilantic IV [Member]
Schedule of Investments [Line Items]
Investment					1,178,000					1,178,000
Distribution Made to Limited Partner, Cash Distributions Paid										194,000
Trilantic V [Member]
Schedule of Investments [Line Items]
Investment	155,000				4,980,000				155,000	4,980,000
Distribution Made to Limited Partner, Cash Distributions Paid										1,549,000
Capital Commitment	5,000,000								5,000,000
Unfunded Commitments for Capital Contributions	391,000								391,000
Trilantic [Member]
Schedule of Investments [Line Items]
Investment	6,762,000				9,932,000				6,762,000	9,932,000
Issued LP Units (in shares)													500,000
Limited Partnership Investment													$ 16,090,000
Glisco [Member]
Schedule of Investments [Line Items]
Equity Securities without Readily Determinable Fair Value, Amount	$ 899,000				$ 1,609,000				$ 899,000	$ 1,609,000