Investments - Company's Investments and Securities Sold, Not Yet Purchased (Detail) - USD ($) $ in Thousands	Sep. 30, 2022	Dec. 31, 2021
Schedule of Investments [Line Items]
Total investments	$ 638,960	$ 1,007,339
Investments, at fair value	623,222	991,089
Securities sold, not yet purchased, at fair value (included in "other liabilities")	4,301	6,828
Debt [Member]
Schedule of Investments [Line Items]
Total investments		299,990
Investments, at fair value		299,990
Equities [Member]
Schedule of Investments [Line Items]
Total investments	39,747	54,040
Investments, at fair value	39,747	54,040
Alternative Investment Funds [Member]
Schedule of Investments [Line Items]
Total investments	54,201	49,757
Investments, at fair value	54,201	49,757
Debt Funds [Member]
Schedule of Investments [Line Items]
Total investments	167,763	164,952
Investments, at fair value	167,763	164,952
Equity Funds [Member]
Schedule of Investments [Line Items]
Total investments	319,707	375,761
Investments, at fair value	319,707	375,761
Private Equity Funds [Member]
Schedule of Investments [Line Items]
Total investments	41,804	46,589
Investments, at fair value	41,804	46,589
Funds Total [Member]
Schedule of Investments [Line Items]
Total investments	583,475	637,059
Equity Method [Member]
Schedule of Investments [Line Items]
Total investments	$ 15,738	$ 16,250