Comprehensive Income and Accumulated Other Comprehensive Income - Reclassification Out of Accumulated Other Comprehensive Income (Detail) - USD ($) $ in Thousands	3 Months Ended
	Mar. 31, 2022	Mar. 31, 2021
Reclassification Adjustment Out Of Accumulated Other Comprehensive Income [Line Items]
Net realized gains on investments	$ 738	$ 319
Income before income taxes	21,422	23,625
Income tax expense	(4,091)	(4,313)
Net income	17,331	19,312
Unrealized Gains On Debt Securities, Net Of Tax [Member] | Reclassification Out of Accumulated Other Comprehensive Income [Member]
Reclassification Adjustment Out Of Accumulated Other Comprehensive Income [Line Items]
Net realized gains on investments	393	396
Income before income taxes	393	396
Income tax expense	(83)	(83)
Net income	$ 310	$ 313