Investments - Company's Investments and Securities Sold, Not Yet Purchased (Detail) - USD ($) $ in Thousands	Mar. 31, 2022	Dec. 31, 2021
Schedule of Investments [Line Items]
Total investments	$ 869,844	$ 1,007,339
Equity method	16,167	16,250
Investments, at fair value	853,677	991,089
Securities sold, not yet purchased, at fair value (included in "other liabilities")	5,726	6,828
Debt [Member]
Schedule of Investments [Line Items]
Total investments	99,845	299,990
Investments, at fair value	99,845	299,990
Equities [Member]
Schedule of Investments [Line Items]
Total investments	53,497	54,040
Investments, at fair value	53,497	54,040
Alternative Investment Funds [Member]
Schedule of Investments [Line Items]
Total investments	55,390	49,757
Investments, at fair value	55,390	49,757
Debt Funds [Member]
Schedule of Investments [Line Items]
Total investments	195,767	164,952
Investments, at fair value	195,767	164,952
Equity Funds [Member]
Schedule of Investments [Line Items]
Total investments	400,586	375,761
Investments, at fair value	400,586	375,761
Private Equity Funds [Member]
Schedule of Investments [Line Items]
Total investments	48,592	46,589
Investments, at fair value	48,592	46,589
Funds Total [Member]
Schedule of Investments [Line Items]
Total investments	700,335	637,059
Equity Method [Member]
Schedule of Investments [Line Items]
Total investments	$ 16,167	$ 16,250