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Schedule of Total Investment Return (Detail) - USD ($) $ in Thousands | 3 Months Ended
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Mar. 31, 2024 | Mar. 31, 2023
Investments, Debt and Equity Securities [Abstract] |  |  |
Net investment income |  | $ 14,520 | $ 12,008
Net realized investment losses (gains) |  | 847 | (1,520)
Change in unrealized holding gains |  | 3,547 | 10,480
Net realized and unrealized investment returns |  | 4,394 | 8,960
Total investment return |  | $ 18,914 | $ 20,968
Total investment return % | [1] | 1.30% | 1.60%
Average investment portfolio | [2] | $ 1,403,878 | $ 1,344,886
[1] | Not annualized.
[2] | Average of total cash and invested assets, net of receivable/payable for securities, as of the beginning and end of the period.

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- Definition Amount, after investment expense, of income earned from investments in securities and real estate. Includes, but is not limited to, real estate investment, policy loans, dividends, and interest. Excludes realized gain (loss) on investments. + References Reference 1: http://www.xbrl.org/2003/role/exampleRef -Topic 946 -SubTopic 830 -Name Accounting Standards Codification -Section 55 -Paragraph 10 -Publisher FASB -URI https://asc.fasb.org//1943274/2147480167/946-830-55-10 Reference 2: http://www.xbrl.org/2003/role/disclosureRef -Topic 944 -SubTopic 220 -Name Accounting Standards Codification -Section S99 -Paragraph 1 -Subparagraph (SX 210.7-04(2)(d)) -Publisher FASB -URI https://asc.fasb.org//1943274/2147483586/944-220-S99-1 Reference 3: http://www.xbrl.org/2003/role/disclosureRef -Topic 946 -SubTopic 220 -Name Accounting Standards Codification -Section S99 -Paragraph 1 -Subparagraph (SX 210.6-07(4)) -Publisher FASB -URI https://asc.fasb.org//1943274/2147483575/946-220-S99-1 Reference 4: http://www.xbrl.org/2003/role/disclosureRef -Topic 944 -SubTopic 220 -Name Accounting Standards Codification -Section S99 -Paragraph 1 -Subparagraph (SX 210.7-04(2)) -Publisher FASB -URI https://asc.fasb.org//1943274/2147483586/944-220-S99-1 Reference 5: http://www.xbrl.org/2003/role/disclosureRef -Name Accounting Standards Codification -Section 45 -Paragraph 5 -SubTopic 220 -Topic 946 -Publisher FASB -URI https://asc.fasb.org//1943274/2147483581/946-220-45-5 + Details
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