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Schedule VI - Supplementary Information Concerning Property-Casualty Insurance Operations (Details) - USD ($) $ in Thousands | 12 Months Ended
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Dec. 31, 2023 | Dec. 31, 2022 | Dec. 31, 2021
SEC Schedule, 12-18, Supplemental Information, Property-Casualty Insurance Underwriters [Abstract] |  |  |
Deferred policy acquisition costs | $ 861,609 | $ 763,486 | $ 676,145
Reserves for losses and loss expenses | 18,739,652 | 17,011,223 | 15,390,888
Unearned premiums | 5,922,326 | 5,297,654 | 4,847,160
Net premiums earned | 10,400,687 | 9,561,429 | 8,106,031
Net investment income | 1,052,835 | 779,185 | 671,618
Losses and loss expenses incurred: |  |  |
Current year | 6,311,780 | 5,774,713 | 4,921,191
Prior years | 29,681 | 54,511 | 863
Loss reserve discount accretion | 30,681 | 32,526 | 31,906
Amortization of deferred policy acquisition costs |  | 1,038,903 | 961,628
Paid losses and loss expenses | 4,981,610 | 4,347,910 | 3,665,694
Net premiums written | $ 10,954,467 | $ 10,004,070 | $ 8,862,867

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- Definition Amount of amortization expense on deferred policy acquisition cost for property-casualty insurance underwriter. + References Reference 1: http://www.xbrl.org/2003/role/disclosureRef -Topic 944 -SubTopic 235 -Name Accounting Standards Codification -Section S99 -Paragraph 3 -Subparagraph (SX 210.12-18(Column I)) -Publisher FASB -URI https://asc.fasb.org//1943274/2147480149/944-235-S99-3 + Details
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- Definition Amount, after effects of reinsurance, of expense for claims incurred in the current reporting period and related claims settlement costs. + References Reference 1: http://www.xbrl.org/2003/role/disclosureRef -Topic 944 -SubTopic 40 -Name Accounting Standards Codification -Section 50 -Paragraph 3 -Subparagraph (b) -Publisher FASB -URI https://asc.fasb.org//1943274/2147480081/944-40-50-3 + Details
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- Definition Amount of loss reported and paid for claim and claim adjustment expense by property-casualty insurance underwriter. + References Reference 1: http://www.xbrl.org/2003/role/disclosureRef -Topic 944 -SubTopic 235 -Name Accounting Standards Codification -Section S99 -Paragraph 3 -Subparagraph (SX 210.12-18(Column J)) -Publisher FASB -URI https://asc.fasb.org//1943274/2147480149/944-235-S99-3 + Details
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