Comprehensive Income and Accumulated Other Comprehensive Income - Reclassification Out of Accumulated Other Comprehensive Income (Detail) - USD ($) $ in Thousands	12 Months Ended
	Dec. 31, 2021	Dec. 31, 2020	Dec. 31, 2019
Reclassification Adjustment Out Of Accumulated Other Comprehensive Income [Line Items]
Net realized gains (losses) on investments	$ 1,695	$ 1,132	$ (80)
Income before income taxes	79,449	106,919	115,517
Income tax expense	(13,693)	(20,317)	(22,827)
Net income	65,756	86,602	92,690
Unrealized Gains (losses) on Available-for-Sale Securities [Member] | Reclassification Out of Accumulated Other Comprehensive Income [Member]
Reclassification Adjustment Out Of Accumulated Other Comprehensive Income [Line Items]
Net realized gains (losses) on investments	2,776	925	(841)
Income before income taxes	2,776	925	(841)
Income tax expense	(583)	(195)	177
Net income	$ 2,193	$ 730	$ (664)