Comprehensive Income and Accumulated Other Comprehensive Income (Loss) - Reclassification Out of Accumulated Other Comprehensive Income (Loss) (Detail) - USD ($) $ in Thousands	3 Months Ended		9 Months Ended
	Sep. 30, 2022	Sep. 30, 2021	Sep. 30, 2022	Sep. 30, 2021
Reclassification Adjustment Out Of Accumulated Other Comprehensive Income [Line Items]
Net realized gains (losses) on investments	$ 585	$ (8)	$ 2,402	$ 1,490
Income before income taxes	13,451	24,721	41,996	77,517
Income tax expense	(2,090)	(5,585)	(7,172)	(15,302)
Net income	11,361	19,136	34,824	62,215
Unrealized Gains On Debt Securities, Net Of Tax [Member] | Reclassification Out of Accumulated Other Comprehensive Income (Loss) [Member]
Reclassification Adjustment Out Of Accumulated Other Comprehensive Income [Line Items]
Net realized gains (losses) on investments	1,061	331	1,955	2,307
Income before income taxes	1,061	331	1,955	2,307
Income tax expense	(223)	(69)	(410)	(484)
Net income	$ 838	$ 262	$ 1,545	$ 1,823