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Reinsurance - Reinsurance Arrangements (Detail) - USD ($) $ in Thousands	3 Months Ended								12 Months Ended
	Dec. 31, 2023	Sep. 30, 2023	Jun. 30, 2023	Mar. 31, 2023	Dec. 31, 2022	Sep. 30, 2022	Jun. 30, 2022	Mar. 31, 2022	Dec. 31, 2023	Dec. 31, 2022	Dec. 31, 2021
Reinsurance Disclosures [Abstract]
Direct premiums written	$ 432,600								$ 1,921,833	$ 1,845,786	$ 1,671,252
Ceded premiums written									(577,020)	(672,508)	(586,425)
Net premiums written									1,344,813	1,173,278	1,084,827
Direct premiums earned									1,875,129	1,759,701	1,596,618
Ceded premiums earned									(623,193)	(631,075)	(561,155)
Premiums earned, net	$ 335,398	$ 331,040	$ 303,274	$ 282,224	$ 291,870	$ 290,631	$ 277,061	$ 269,064	1,251,936	1,128,626	1,035,463
Direct Losses and Loss Adjustment Expenses									1,046,854	1,972,541	1,189,444
Ceded Losses and Loss Adjustment Expenses									(54,218)	(1,034,142)	(410,239)
Net Losses and Loss Adjustment Expenses									$ 992,636	$ 938,399	$ 779,205