Investments - Summary of Net Investment Income (Detail) - USD ($) $ in Thousands	3 Months Ended		9 Months Ended
	Sep. 30, 2023	Sep. 30, 2022	Sep. 30, 2023	Sep. 30, 2022
Schedule of Available-for-sale Securities [Line Items]
Net investment income	$ 7,197	$ 3,400	$ 20,613	$ 8,575
Less: Investment expenses	330	513	1,565	1,525
Net investment income, less investment expenses	6,867	2,887	19,048	7,050
Debt Securities [Member]
Schedule of Available-for-sale Securities [Line Items]
Net investment income	4,685	2,992	12,723	7,695
Equity Securities[Member]
Schedule of Available-for-sale Securities [Line Items]
Net investment income	79	0	170	0
Cash and Cash Equivalents [Member]
Schedule of Available-for-sale Securities [Line Items]
Net investment income	1,746	273	6,195	433
Other Investments [Member]
Schedule of Available-for-sale Securities [Line Items]
Net investment income	$ 687	$ 135	$ 1,525	$ 447