Comprehensive Income and Accumulated Other Comprehensive Loss - Reclassification Out of Accumulated Other Comprehensive Income (Loss) (Detail) - USD ($) $ in Thousands	3 Months Ended		9 Months Ended
	Sep. 30, 2023	Sep. 30, 2022	Sep. 30, 2023	Sep. 30, 2022
Reclassification Adjustment Out Of Accumulated Other Comprehensive Income [Line Items]
Net realized gains on investments	$ 5,133	$ 585	$ 5,466	$ 2,402
Income before income taxes	12,327	13,451	53,430	41,996
Income tax expense	(2,366)	(2,090)	(10,503)	(7,172)
Net income	9,961	11,361	42,927	34,824
Unrealized Gains (Losses) On Debt Securities, Net Of Tax [Member] | Reclassification Out of Accumulated Other Comprehensive Loss [Member]
Reclassification Adjustment Out Of Accumulated Other Comprehensive Income [Line Items]
Net realized gains on investments	(243)	1,061	(438)	1,955
Income before income taxes	(243)	1,061	(438)	1,955
Income tax expense	51	(223)	92	(410)
Net income	$ (192)	$ 838	$ (346)	$ 1,545