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Investments - Realized and Unrealized Gains and Losses related to Marketable Equity Securities (Detail) - USD ($)
$ in Thousands
3 Months Ended 6 Months Ended
Jun. 30, 2021
Jun. 30, 2020
Jun. 30, 2021
Jun. 30, 2020
Investments Debt And Equity Securities [Abstract]        
Realized gain (loss) on equity securities sold $ (79) $ 328 $ (55) $ (2,108)
Unrealized gain on equity securities held 2,011 9,353 2,912 889
Total gain (loss) recognized, net $ 1,932 $ 9,681 $ 2,857 $ (1,219)