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Investments - Investments in Variable Interest Entities (Detail) - USD ($)
Sep. 30, 2021
Dec. 31, 2020
Variable Interest Entity [Line Items]    
Maximum Exposure to Loss $ 4,900,000 $ 4,800,000
Variable Interest Entity, Not Primary Beneficiary    
Variable Interest Entity [Line Items]    
Investment 1,044,000 1,258,000
Maximum Exposure to Loss $ 2,024,000 $ 2,238,000