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Investments - Realized and Unrealized Gains and Losses related to Marketable Equity Securities (Detail) - USD ($)
$ in Thousands
3 Months Ended 9 Months Ended
Sep. 30, 2021
Sep. 30, 2020
Sep. 30, 2021
Sep. 30, 2020
Investments Debt And Equity Securities [Abstract]        
Realized gain (loss) on equity securities sold   $ 623 $ (55) $ (1,485)
Unrealized (loss) gain on equity securities held $ (68) 2,157 2,844 3,046
Total gain (loss) recognized, net $ (68) $ 2,780 $ 2,789 $ 1,561