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Investments - Summary of Details on Realized and Unrealized Gains and Losses Related to Equity Securities (Detail) - USD ($) $ in Thousands | 3 Months Ended | 6 Months Ended
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Jun. 30, 2021 | Jun. 30, 2020 | Jun. 30, 2021 | Jun. 30, 2020
Investments, Debt and Equity Securities [Abstract] |  |  |  |
Unrealized gains (losses) recognized during the reported period on equity securities still held at the end of the reported period | $ 1,546 | $ 3,871 | $ 1,027 | $ (4,154)

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- Definition Amount of unrealized gain (loss) on investment. + References Reference 1: http://fasb.org/us-gaap/role/ref/legacyRef -Publisher FASB -Name Accounting Standards Codification -Topic 230 -SubTopic 10 -Section 45 -Paragraph 28 -Subparagraph (b) -URI http://asc.fasb.org/extlink&oid=123570139&loc=d3e3602-108585 + Details
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