Liability for Unpaid Losses and Loss Adjustment Expenses - Summary of Incurred Claims and Allocated Claim Adjustment Expenses, Net of Reinsurance (Detail) $ in Thousands	Dec. 31, 2023 USD ($) Claim	Dec. 31, 2022 USD ($)	Dec. 31, 2021 USD ($)	Dec. 31, 2020 USD ($)	Dec. 31, 2019 USD ($)
Claims Development [Line Items]
Incurred Loss and Defense & Cost Containment Expenses, Net of Reinsurance	$ 3,450,253
Accident Year 2019
Claims Development [Line Items]
Incurred Loss and Defense & Cost Containment Expenses, Net of Reinsurance	487,459	$ 470,372	$ 467,198	$ 452,029	$ 446,419
Total of IBNR Plus Expected Development (Redundancy) on Reported Claims	$ (4,404)
Cumulative Number of Reported Claims | Claim	47,695
Accident Year 2020
Claims Development [Line Items]
Incurred Loss and Defense & Cost Containment Expenses, Net of Reinsurance	$ 725,486	635,412	637,764	$ 617,795
Total of IBNR Plus Expected Development (Redundancy) on Reported Claims	$ (4,604)
Cumulative Number of Reported Claims | Claim	81,106
Accident Year 2021
Claims Development [Line Items]
Incurred Loss and Defense & Cost Containment Expenses, Net of Reinsurance	$ 695,957	646,977	$ 641,679
Total of IBNR Plus Expected Development (Redundancy) on Reported Claims	$ (19,332)
Cumulative Number of Reported Claims | Claim	60,580
Accident Year 2022
Claims Development [Line Items]
Incurred Loss and Defense & Cost Containment Expenses, Net of Reinsurance	$ 717,840	$ 793,341
Total of IBNR Plus Expected Development (Redundancy) on Reported Claims	$ (19,946)
Cumulative Number of Reported Claims | Claim	103,936
Accident Year 2023
Claims Development [Line Items]
Incurred Loss and Defense & Cost Containment Expenses, Net of Reinsurance	$ 823,511
Total of IBNR Plus Expected Development (Redundancy) on Reported Claims	$ 344,113
Cumulative Number of Reported Claims | Claim	45,849