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Investment Information - Other investments and other investable assets (Details) - USD ($) $ in Thousands | Dec. 31, 2020 | Dec. 31, 2019
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Fair Value, Option, Quantitative Disclosures [Line Items] |  |
Investments accounted for using the fair value option | $ 3,824,796 | $ 3,663,477
Other investable assets | 500,000 | 0
Total other investments | 4,324,796 | 3,663,477
Fixed maturities |  |
Fair Value, Option, Quantitative Disclosures [Line Items] |  |
Investments accounted for using the fair value option | 843,354 | 754,452
Other investments |  |
Fair Value, Option, Quantitative Disclosures [Line Items] |  |
Investments accounted for using the fair value option | 2,331,885 | 2,429,316
Short-term investments |  |
Fair Value, Option, Quantitative Disclosures [Line Items] |  |
Investments accounted for using the fair value option | 557,008 | 377,014
Equity securities |  |
Fair Value, Option, Quantitative Disclosures [Line Items] |  |
Investments accounted for using the fair value option | $ 92,549 | $ 102,695

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