Investments - Additional Information (Details)	1 Months Ended	3 Months Ended		6 Months Ended
	Jul. 31, 2021 USD ($) director	Jun. 30, 2021 USD ($) shares	Jun. 30, 2020 USD ($) shares	Jun. 30, 2021 USD ($) shares	Jun. 30, 2020 USD ($) shares	Dec. 31, 2020 USD ($)	Dec. 31, 2010 USD ($) shares
Schedule of Investments [Line Items]
Income from Equity Method Investments		$ 3,394,000	$ 2,313,000	$ 6,418,000	$ 5,441,000
Net Realized and Unrealized Gains (Losses) on Private Equity Fund Investments		(17,000)	(2,255,000)	22,000	(2,343,000)
Previously Received Carried Interest Subject to Repayment		761,000		761,000
Total Assets		2,947,448,000	$ 2,499,589,000	2,947,448,000	$ 2,499,589,000	$ 3,370,888,000
Variable Interest Entity, Reporting Entity Involvement, Maximum Loss Exposure, Amount		$ 5,995,000		$ 5,995,000		5,572,000
Issued LP Units (in shares) | shares		0	0	0	0
Unfunded Commitments for Capital Contributions		$ 10,091,000		$ 10,091,000
Equity Securities without Readily Determinable Fair Value, Amount		691,000		691,000		683,000
Variable Interest Entity, Not Primary Beneficiary [Member]
Schedule of Investments [Line Items]
Total Assets		3,560,000		3,560,000		3,083,000
Equity Method Investments [Member]
Schedule of Investments [Line Items]
Amortization of Intangible Assets		$ 79,000	$ 79,000	$ 158,000	$ 158,000
ABS [Member]
Schedule of Investments [Line Items]
Equity Method Investment, Ownership Percentage		46.00%		46.00%
Income from Equity Method Investments		$ 2,295,000	1,803,000	$ 4,490,000	3,823,000
Atalanta Sosnoff [Member]
Schedule of Investments [Line Items]
Equity Method Investment, Ownership Percentage		49.00%		49.00%
Income from Equity Method Investments		$ 550,000	445,000	$ 1,210,000	1,017,000
Luminis [Member]
Schedule of Investments [Line Items]
Equity Method Investment, Ownership Percentage		20.00%		20.00%
Income from Equity Method Investments		$ 549,000	$ 65,000	$ 718,000	$ 601,000
Seneca Evercore | Subsequent Event [Member]
Schedule of Investments [Line Items]
Equity Method Investment, Ownership Percentage	20.00%
Payments to Acquire Equity Method Investments	$ 500,000
Number of Dirctors | director	1
G5 [Member]
Schedule of Investments [Line Items]
Debt Securities, Held-to-maturity						7,385,000
G5 [Member] | Other Income
Schedule of Investments [Line Items]
Debt Securities, Gain (Loss)		4,374,000		4,374,000
Trilantic [Member]
Schedule of Investments [Line Items]
Issued LP Units (in shares) | shares							500,000
Limited Partnership Investment							$ 16,090,000
Investment		5,293,000		5,293,000		6,623,000
Trilantic IV [Member]
Schedule of Investments [Line Items]
Investment						1,178,000
Trilantic V [Member]
Schedule of Investments [Line Items]
Investment		5,000		5,000		5,164,000
Capital Commitment		5,000,000		5,000,000
Unfunded Commitments for Capital Contributions		367,000		367,000
Trilantic VI [Member]
Schedule of Investments [Line Items]
Investment		1,325,000		1,325,000		3,125,000
Capital Commitment		12,000,000		12,000,000
Unfunded Commitments for Capital Contributions		7,229,000		7,229,000
Glisco [Member]
Schedule of Investments [Line Items]
Equity Securities without Readily Determinable Fair Value, Amount		$ 221,000		$ 221,000		$ 387,000