Comprehensive Income and Accumulated Other Comprehensive Income - Reclassification Out of Accumulated Other Comprehensive Income (Detail) - USD ($) $ in Thousands	12 Months Ended
	Dec. 31, 2022	Dec. 31, 2021	Dec. 31, 2020
Reclassification Adjustment Out Of Accumulated Other Comprehensive Income [Line Items]
Net realized gains on investments	$ 3,440	$ 1,695	$ 1,132
Income before income taxes	67,646	79,449	106,919
Income tax expense	(12,044)	(13,693)	(20,317)
Net income	55,602	65,756	86,602
Unrealized Gains on Available-for-Sale Securities [Member] | Reclassification Out of Accumulated Other Comprehensive Income (Loss) [Member]
Reclassification Adjustment Out Of Accumulated Other Comprehensive Income [Line Items]
Net realized gains on investments	3,037	2,776	925
Income before income taxes	3,037	2,776	925
Income tax expense	(638)	(583)	(195)
Net income	$ 2,399	$ 2,193	$ 730