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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, 2022 USD ($) Claim | Dec. 31, 2021 USD ($) | 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 ($) | Dec. 31, 2013 USD ($)
Claims Development [Line Items] |  |  |  |  |  |  |  |  |  |
Incurred Losses and Allocated Loss Adjustment Expenses, Net of Reinsurance | $ 2,083,934 |  |  |  |  |  |  |  |  |
Total IBNR Plus Expected Development on Reported Claims | 57,308 |  |  |  |  |  |  |  |  |
Cumulative Paid Losses and Allocated Loss Adjustment Expenses, Net of Reinsurance | 1,593,043 |  |  |  |  |  |  |  |  |
All outstanding liabilities before 2013, net of reinsurance | 92,591 |  |  |  |  |  |  |  |  |
Liabilities for loss and loss adjustment expenses, net of reinsurance | 583,482 |  |  |  |  |  |  |  |  |
Accident Year 2013 [Member] |  |  |  |  |  |  |  |  |  |
Claims Development [Line Items] |  |  |  |  |  |  |  |  |  |
Incurred Losses and Allocated Loss Adjustment Expenses, Net of Reinsurance | 204,026 | $ 205,421 | $ 207,304 | $ 209,184 | $ 210,588 | $ 214,701 | $ 220,457 | $ 233,656 | $ 241,811 | $ 241,810
Total IBNR Plus Expected Development on Reported Claims | $ 6,435 |  |  |  |  |  |  |  |  |
Cumulative Number of Claims Reported | Claim | 5,768 |  |  |  |  |  |  |  |  |
Cumulative Paid Losses and Allocated Loss Adjustment Expenses, Net of Reinsurance | $ 184,500 | 183,365 | 182,465 | 180,614 | 177,724 | 172,479 | 165,994 | 150,304 | 119,507 | $ 51,396
Claim Frequency | 16.56% |  |  |  |  |  |  |  |  |
Accident Year 2014 [Member] |  |  |  |  |  |  |  |  |  |
Claims Development [Line Items] |  |  |  |  |  |  |  |  |  |
Incurred Losses and Allocated Loss Adjustment Expenses, Net of Reinsurance | $ 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 | $ 4,510 |  |  |  |  |  |  |  |  |
Cumulative Number of Claims Reported | Claim | 5,841 |  |  |  |  |  |  |  |  |
Cumulative Paid Losses and Allocated Loss Adjustment Expenses, Net of Reinsurance | $ 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 | $ 207,086 | 207,929 | 211,758 | 220,965 | 235,471 | 252,514 | 262,573 | 262,573 |  |
Total IBNR Plus Expected Development on Reported Claims | $ 4,415 |  |  |  |  |  |  |  |  |
Cumulative Number of Claims Reported | Claim | 5,516 |  |  |  |  |  |  |  |  |
Cumulative Paid Losses and Allocated Loss Adjustment Expenses, Net of Reinsurance | $ 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 | $ 201,604 | 202,820 | 209,214 | 218,005 | 241,406 | 250,491 | 250,491 |  |  |
Total IBNR Plus Expected Development on Reported Claims | $ 4,452 |  |  |  |  |  |  |  |  |
Cumulative Number of Claims Reported | Claim | 5,393 |  |  |  |  |  |  |  |  |
Cumulative Paid Losses and Allocated Loss Adjustment Expenses, Net of Reinsurance | $ 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 | $ 208,360 | 211,964 | 220,096 | 234,587 | 244,098 | 244,094 |  |  |  |
Total IBNR Plus Expected Development on Reported Claims | $ 4,939 |  |  |  |  |  |  |  |  |
Cumulative Number of Claims Reported | Claim | 5,212 |  |  |  |  |  |  |  |  |
Cumulative Paid Losses and Allocated Loss Adjustment Expenses, Net of Reinsurance | $ 183,696 | 175,733 | 166,448 | 151,427 | 122,552 | $ 56,951 |  |  |  |
Claim Frequency | 14.68% |  |  |  |  |  |  |  |  |
Accident Year 2018 [Member] |  |  |  |  |  |  |  |  |  |
Claims Development [Line Items] |  |  |  |  |  |  |  |  |  |
Incurred Losses and Allocated Loss Adjustment Expenses, Net of Reinsurance | $ 208,517 | 217,369 | 235,641 | 250,487 | 250,487 |  |  |  |  |
Total IBNR Plus Expected Development on Reported Claims | $ 5,268 |  |  |  |  |  |  |  |  |
Cumulative Number of Claims Reported | Claim | 5,471 |  |  |  |  |  |  |  |  |
Cumulative Paid Losses and Allocated Loss Adjustment Expenses, Net of Reinsurance | $ 181,081 | 172,423 | 152,328 | 126,057 | $ 62,061 |  |  |  |  |
Claim Frequency | 15.21% |  |  |  |  |  |  |  |  |
Accident Year 2019 [Member] |  |  |  |  |  |  |  |  |  |
Claims Development [Line Items] |  |  |  |  |  |  |  |  |  |
Incurred Losses and Allocated Loss Adjustment Expenses, Net of Reinsurance | $ 214,123 | 227,246 | 241,344 | 241,344 |  |  |  |  |  |
Total IBNR Plus Expected Development on Reported Claims | $ 8,550 |  |  |  |  |  |  |  |  |
Cumulative Number of Claims Reported | Claim | 5,218 |  |  |  |  |  |  |  |  |
Cumulative Paid Losses and Allocated Loss Adjustment Expenses, Net of Reinsurance | $ 168,448 | 154,391 | 120,512 | $ 58,884 |  |  |  |  |  |
Claim Frequency | 15.26% |  |  |  |  |  |  |  |  |
Accident Year 2020 [Member] |  |  |  |  |  |  |  |  |  |
Claims Development [Line Items] |  |  |  |  |  |  |  |  |  |
Incurred Losses and Allocated Loss Adjustment Expenses, Net of Reinsurance | $ 214,500 | 220,710 | 220,710 |  |  |  |  |  |  |
Total IBNR Plus Expected Development on Reported Claims | $ 17,039 |  |  |  |  |  |  |  |  |
Cumulative Number of Claims Reported | Claim | 4,387 |  |  |  |  |  |  |  |  |
Cumulative Paid Losses and Allocated Loss Adjustment Expenses, Net of Reinsurance | $ 137,411 | 109,882 | $ 50,113 |  |  |  |  |  |  |
Claim Frequency | 13.94% |  |  |  |  |  |  |  |  |
Accident Year 2021 [Member] |  |  |  |  |  |  |  |  |  |
Claims Development [Line Items] |  |  |  |  |  |  |  |  |  |
Incurred Losses and Allocated Loss Adjustment Expenses, Net of Reinsurance | $ 222,715 | 222,715 |  |  |  |  |  |  |  |
Total IBNR Plus Expected Development on Reported Claims | $ (5,162) |  |  |  |  |  |  |  |  |
Cumulative Number of Claims Reported | Claim | 4,273 |  |  |  |  |  |  |  |  |
Cumulative Paid Losses and Allocated Loss Adjustment Expenses, Net of Reinsurance | $ 130,288 | $ 52,292 |  |  |  |  |  |  |  |
Claim Frequency | 14.92% |  |  |  |  |  |  |  |  |
Accident Year 2022 [Member] |  |  |  |  |  |  |  |  |  |
Claims Development [Line Items] |  |  |  |  |  |  |  |  |  |
Incurred Losses and Allocated Loss Adjustment Expenses, Net of Reinsurance | $ 192,907 |  |  |  |  |  |  |  |  |
Total IBNR Plus Expected Development on Reported Claims | $ 6,863 |  |  |  |  |  |  |  |  |
Cumulative Number of Claims Reported | Claim | 3,886 |  |  |  |  |  |  |  |  |
Cumulative Paid Losses and Allocated Loss Adjustment Expenses, Net of Reinsurance | $ 50,954 |  |  |  |  |  |  |  |  |
Claim Frequency | 13.77% |  |  |  |  |  |  |  |  |

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