Investments - Additional Information (Details) - USD ($)	3 Months Ended								12 Months Ended
	Dec. 31, 2018	Sep. 30, 2018	Jun. 30, 2018	Mar. 31, 2018	Dec. 31, 2017	Sep. 30, 2017	Jun. 30, 2017	Mar. 31, 2017	Dec. 31, 2018	Dec. 31, 2017	Dec. 31, 2016	Jan. 31, 2019	May 31, 2017	Dec. 31, 2010
Schedule of Investments [Line Items]
Income from Equity Method Investments	$ 2,452,000	$ 2,298,000	$ 2,419,000	$ 2,125,000	$ 3,331,000	$ 1,827,000	$ 2,070,000	$ 1,610,000	$ 9,294,000	$ 8,838,000	$ 6,641,000
Amortization of Intangible Assets									9,199,000	9,793,000	11,640,000
Equity Method Investment	58,507,000				59,856,000				58,507,000	59,856,000
Marketable Securities	204,627,000				65,032,000				204,627,000	65,032,000
Net Realized and Unrealized Gains (Losses) on Private Equity Fund Investments, Including Performance Fees									(397,000)	(915,000)	7,616,000
Previously Received Carried Interest Subject to Repayment	0								0
Variable Interest Entity, Nonconsolidated, Carrying Amount, Assets	5,445,000				8,730,000				5,445,000	8,730,000
Variable Interest Entity, Reporting Entity Involvement, Maximum Loss Exposure, Amount	8,048,000				10,996,000				8,048,000	10,996,000
Unfunded Commitments for Capital Contributions	15,244,000								15,244,000
Equity Securities without Readily Determinable Fair Value, Amount	1,079,000				1,079,000				1,079,000	1,079,000
Equity Method Investments [Member]
Schedule of Investments [Line Items]
Amortization of Intangible Assets									893,000	1,505,000	3,533,000
Private Equity Funds [Member]
Schedule of Investments [Line Items]
Equity Method Investment	$ 9,800,000				13,812,000				9,800,000	13,812,000
Investment Management [Member]
Schedule of Investments [Line Items]
Income from Equity Method Investments									8,776,000	8,561,000	5,271,000
Investment Banking [Member]
Schedule of Investments [Line Items]
Income from Equity Method Investments									$ 518,000	277,000	1,370,000
ABS [Member]
Schedule of Investments [Line Items]
Equity Method Investment, Ownership Percentage	46.00%								46.00%
Income from Equity Method Investments									$ 7,565,000	7,990,000	4,913,000
Equity Method Investment	$ 38,699,000				39,894,000				$ 38,699,000	39,894,000
Atalanta Sosnoff [Member]
Schedule of Investments [Line Items]
Equity Method Investment, Ownership Percentage	49.00%								49.00%
Income from Equity Method Investments									$ 1,211,000	493,000	574,000
Equity Method Investment	$ 13,291,000				13,963,000				$ 13,291,000	13,963,000
Atalanta Sosnoff [Member] | Special Charges [Member] | Investment Management [Member]
Schedule of Investments [Line Items]
Equity Method Investment, Other than Temporary Impairment											8,100,000
Luminis [Member]
Schedule of Investments [Line Items]
Equity Method Investment, Ownership Percentage	19.00%								19.00%
Income from Equity Method Investments									$ 518,000	499,000
Equity Method Investment	$ 6,517,000				5,999,000				6,517,000	5,999,000
G5 [Member]
Schedule of Investments [Line Items]
Income from Equity Method Investments										(144,000)	$ 1,154,000
Equity Method Investment													$ 11,555,000
Debt Securities, Held-to-maturity	9,717,000				10,995,000				9,717,000	10,995,000
G5 [Member] | Special Charges [Member] | Investment Banking [Member]
Schedule of Investments [Line Items]
Equity Method Investment, Other than Temporary Impairment										14,400,000
Glisco IV [Member] | Private Equity Funds [Member]
Schedule of Investments [Line Items]
Equity Method Investment	45,000								$ 45,000
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	795,000				833,000				$ 795,000	833,000
Cash	786,000								786,000
Marketable Securities	9,000								9,000
Glisco II [Member]
Schedule of Investments [Line Items]
Distribution Made to Limited Partner, Cash Distributions Paid									2,059,000	2,106,000
Trilantic IV [Member]
Schedule of Investments [Line Items]
Distribution Made to Limited Partner, Cash Distributions Paid									194,000
Investment					1,178,000					1,178,000
Trilantic V [Member]
Schedule of Investments [Line Items]
Distribution Made to Limited Partner, Cash Distributions Paid									1,549,000	2,311,000
Investment	467,000				4,513,000				467,000	4,513,000
Capital Commitment	5,000,000								5,000,000
Unfunded Commitments for Capital Contributions	582,000								582,000
Trilantic [Member]
Schedule of Investments [Line Items]
Issued LP Units (in shares)														500,000
Limited Partnership Investment														$ 16,090,000
Investment	9,932,000				10,399,000				9,932,000	10,399,000
Trilantic VI [Member]
Schedule of Investments [Line Items]
Capital Commitment	12,000,000								12,000,000
Trilantic VI [Member] | Subsequent Event [Member]
Schedule of Investments [Line Items]
Other Ownership Interests, Contributed Capital												$ 2,200,000
Glisco [Member]
Schedule of Investments [Line Items]
Equity Securities without Readily Determinable Fair Value, Amount	$ 1,609,000				$ 2,172,000				$ 1,609,000	$ 2,172,000