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Loss and Loss Adjustment Expenses - Development Tables of Incurred and Paid Losses and Allocated Loss Adjustment Expenses Net of Reinsurance (Detail) $ in Thousands | 12 Months Ended |  |  |  |  |  |  |  |  |
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Dec. 31, 2023 USD ($) Claim | Dec. 31, 2022 USD ($) | Dec. 31, 2021 USD ($) | Dec. 31, 2020 USD ($) | Dec. 31, 2019 USD ($) | Dec. 31, 2018 USD ($) | Dec. 31, 2017 USD ($) | Dec. 31, 2016 USD ($) | Dec. 31, 2015 USD ($) | Dec. 31, 2014 USD ($)
Claims Development [Line Items] |  |  |  |  |  |  |  |  |  |
Incurred Losses and Allocated Loss Adjustment Expenses, Net of Reinsurance | $ 2,035,580 |  |  |  |  |  |  |  |  |
Total IBNR Plus Expected Development on Reported Claims | 44,927 |  |  |  |  |  |  |  |  |
Cumulative Paid Losses and Allocated Loss Adjustment Expenses, Net of Reinsurance | 1,583,083 |  |  |  |  |  |  |  |  |
All outstanding liabilities before 2012, net of reinsurance | 101,752 |  |  |  |  |  |  |  |  |
Liabilities for loss and loss adjustment expenses, net of reinsurance | 554,248 |  |  |  |  |  |  |  |  |
Accident Year 2014 [Member] |  |  |  |  |  |  |  |  |  |
Claims Development [Line Items] |  |  |  |  |  |  |  |  |  |
Incurred Losses and Allocated Loss Adjustment Expenses, Net of Reinsurance | 209,210 | $ 210,096 | $ 210,811 | $ 212,417 | $ 218,386 | $ 226,933 | $ 235,058 | $ 249,097 | $ 268,846 | $ 268,846
Total IBNR Plus Expected Development on Reported Claims | $ 4,097 |  |  |  |  |  |  |  |  |
Cumulative Number of Claims Reported | Claim | 5,841 |  |  |  |  |  |  |  |  |
Cumulative Paid Losses and Allocated Loss Adjustment Expenses, Net of Reinsurance | $ 195,409 | 193,192 | 192,169 | 191,394 | 186,129 | 180,683 | 169,736 | 153,320 | 119,820 | $ 53,060
Claim Frequency | 14.99% |  |  |  |  |  |  |  |  |
Accident Year 2015 [Member] |  |  |  |  |  |  |  |  |  |
Claims Development [Line Items] |  |  |  |  |  |  |  |  |  |
Incurred Losses and Allocated Loss Adjustment Expenses, Net of Reinsurance | $ 205,556 | 207,086 | 207,929 | 211,758 | 220,965 | 235,471 | 252,514 | 262,573 | 262,573 |
Total IBNR Plus Expected Development on Reported Claims | $ 4,374 |  |  |  |  |  |  |  |  |
Cumulative Number of Claims Reported | Claim | 5,517 |  |  |  |  |  |  |  |  |
Cumulative Paid Losses and Allocated Loss Adjustment Expenses, Net of Reinsurance | $ 190,588 | 189,339 | 188,145 | 185,657 | 182,053 | 170,461 | 151,818 | 121,599 | $ 54,141 |
Claim Frequency | 14.25% |  |  |  |  |  |  |  |  |
Accident Year 2016 [Member] |  |  |  |  |  |  |  |  |  |
Claims Development [Line Items] |  |  |  |  |  |  |  |  |  |
Incurred Losses and Allocated Loss Adjustment Expenses, Net of Reinsurance | $ 198,566 | 201,604 | 202,820 | 209,214 | 218,005 | 241,406 | 250,491 | 250,491 |  |
Total IBNR Plus Expected Development on Reported Claims | $ 4,691 |  |  |  |  |  |  |  |  |
Cumulative Number of Claims Reported | Claim | 5,394 |  |  |  |  |  |  |  |  |
Cumulative Paid Losses and Allocated Loss Adjustment Expenses, Net of Reinsurance | $ 178,572 | 174,134 | 172,133 | 166,887 | 156,860 | 143,016 | 115,713 | $ 52,238 |  |
Claim Frequency | 14.23% |  |  |  |  |  |  |  |  |
Accident Year 2017 [Member] |  |  |  |  |  |  |  |  |  |
Claims Development [Line Items] |  |  |  |  |  |  |  |  |  |
Incurred Losses and Allocated Loss Adjustment Expenses, Net of Reinsurance | $ 206,293 | 208,360 | 211,964 | 220,096 | 234,587 | 244,098 | 244,094 |  |  |
Total IBNR Plus Expected Development on Reported Claims | $ 5,324 |  |  |  |  |  |  |  |  |
Cumulative Number of Claims Reported | Claim | 5,214 |  |  |  |  |  |  |  |  |
Cumulative Paid Losses and Allocated Loss Adjustment Expenses, Net of Reinsurance | $ 185,690 | 183,696 | 175,733 | 166,448 | 151,427 | 122,552 | $ 56,951 |  |  |
Claim Frequency | 14.69% |  |  |  |  |  |  |  |  |
Accident Year 2018 [Member] |  |  |  |  |  |  |  |  |  |
Claims Development [Line Items] |  |  |  |  |  |  |  |  |  |
Incurred Losses and Allocated Loss Adjustment Expenses, Net of Reinsurance | $ 205,001 | 208,517 | 217,369 | 235,641 | 250,487 | 250,487 |  |  |  |
Total IBNR Plus Expected Development on Reported Claims | $ 4,347 |  |  |  |  |  |  |  |  |
Cumulative Number of Claims Reported | Claim | 5,477 |  |  |  |  |  |  |  |  |
Cumulative Paid Losses and Allocated Loss Adjustment Expenses, Net of Reinsurance | $ 184,797 | 181,081 | 172,423 | 152,328 | 126,057 | $ 62,061 |  |  |  |
Claim Frequency | 15.23% |  |  |  |  |  |  |  |  |
Accident Year 2019 [Member] |  |  |  |  |  |  |  |  |  |
Claims Development [Line Items] |  |  |  |  |  |  |  |  |  |
Incurred Losses and Allocated Loss Adjustment Expenses, Net of Reinsurance | $ 206,109 | 214,123 | 227,246 | 241,344 | 241,344 |  |  |  |  |
Total IBNR Plus Expected Development on Reported Claims | $ 5,672 |  |  |  |  |  |  |  |  |
Cumulative Number of Claims Reported | Claim | 5,223 |  |  |  |  |  |  |  |  |
Cumulative Paid Losses and Allocated Loss Adjustment Expenses, Net of Reinsurance | $ 176,488 | 168,448 | 154,391 | 120,512 | $ 58,884 |  |  |  |  |
Claim Frequency | 15.28% |  |  |  |  |  |  |  |  |
Accident Year 2020 [Member] |  |  |  |  |  |  |  |  |  |
Claims Development [Line Items] |  |  |  |  |  |  |  |  |  |
Incurred Losses and Allocated Loss Adjustment Expenses, Net of Reinsurance | $ 207,047 | 214,500 | 220,710 | 220,710 |  |  |  |  |  |
Total IBNR Plus Expected Development on Reported Claims | $ 13,909 |  |  |  |  |  |  |  |  |
Cumulative Number of Claims Reported | Claim | 4,391 |  |  |  |  |  |  |  |  |
Cumulative Paid Losses and Allocated Loss Adjustment Expenses, Net of Reinsurance | $ 153,974 | 137,411 | 109,882 | $ 50,113 |  |  |  |  |  |
Claim Frequency | 13.95% |  |  |  |  |  |  |  |  |
Accident Year 2021 [Member] |  |  |  |  |  |  |  |  |  |
Claims Development [Line Items] |  |  |  |  |  |  |  |  |  |
Incurred Losses and Allocated Loss Adjustment Expenses, Net of Reinsurance | $ 215,232 | 222,715 | 222,715 |  |  |  |  |  |  |
Total IBNR Plus Expected Development on Reported Claims | $ 2,894 |  |  |  |  |  |  |  |  |
Cumulative Number of Claims Reported | Claim | 4,304 |  |  |  |  |  |  |  |  |
Cumulative Paid Losses and Allocated Loss Adjustment Expenses, Net of Reinsurance | $ 159,864 | 130,288 | $ 52,292 |  |  |  |  |  |  |
Claim Frequency | 15.02% |  |  |  |  |  |  |  |  |
Accident Year 2022 [Member] |  |  |  |  |  |  |  |  |  |
Claims Development [Line Items] |  |  |  |  |  |  |  |  |  |
Incurred Losses and Allocated Loss Adjustment Expenses, Net of Reinsurance | $ 192,907 | 192,907 |  |  |  |  |  |  |  |
Total IBNR Plus Expected Development on Reported Claims | $ (12,814) |  |  |  |  |  |  |  |  |
Cumulative Number of Claims Reported | Claim | 4,065 |  |  |  |  |  |  |  |  |
Cumulative Paid Losses and Allocated Loss Adjustment Expenses, Net of Reinsurance | $ 110,494 | $ 50,954 |  |  |  |  |  |  |  |
Claim Frequency | 14.40% |  |  |  |  |  |  |  |  |
Accident Year 2023 [Member] |  |  |  |  |  |  |  |  |  |
Claims Development [Line Items] |  |  |  |  |  |  |  |  |  |
Incurred Losses and Allocated Loss Adjustment Expenses, Net of Reinsurance | $ 189,659 |  |  |  |  |  |  |  |  |
Total IBNR Plus Expected Development on Reported Claims | $ 12,433 |  |  |  |  |  |  |  |  |
Cumulative Number of Claims Reported | Claim | 3,715 |  |  |  |  |  |  |  |  |
Cumulative Paid Losses and Allocated Loss Adjustment Expenses, Net of Reinsurance | $ 47,207 |  |  |  |  |  |  |  |  |
Claim Frequency | 13.09% |  |  |  |  |  |  |  |  |

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