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Investments - Additional Information (Detail) - USD ($)
$ in Millions
Sep. 30, 2024
Dec. 31, 2023
Schedule of Investments [Line Items]    
Total investments $ 184.6 $ 184.7
Partnership Interests in Private Equity Funds    
Schedule of Investments [Line Items]    
Total investments 11.4 11.5
Investments, fair value 10.1 9.2
Equity method investments, fair value 1.3 2.3
Seed Capital Investments [Member]    
Schedule of Investments [Line Items]    
Total investments $ 27.7 $ 26.1