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Schedule of Total Investment Return (Detail) - USD ($) $ in Thousands | 3 Months Ended | 6 Months Ended
--- | --- | ---
Jun. 30, 2023 | Jun. 30, 2022 | Jun. 30, 2023 | Jun. 30, 2022
Investments, Debt and Equity Securities [Abstract] |  |  |  |  |
Net investment income |  | $ 13,216 | $ 1,930 | $ 25,224 | $ 8,522
Net realized investment losses |  | (761) | (9,916) | (2,281) | (35,301)
Change in unrealized holding gains (losses) |  | (3,117) | (17,488) | 7,363 | (41,332)
Net realized and unrealized investment returns |  | (3,878) | (27,404) | 5,082 | (76,633)
Total investment return |  | $ 9,338 | $ (25,474) | $ 30,306 | $ (68,111)
Total investment return % | [1] | 0.70% | (1.80%) | 2.30% | (4.80%)
Average investment portfolio | [2] | $ 1,345,235 | $ 1,395,519 | $ 1,343,024 | $ 1,429,227
[1] | Not annualized.
[2] | Average of total cash and invested assets, net of receivable/payable for securities purchased and sold, as of the beginning and end of the period.

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