Comprehensive Income and Accumulated Other Comprehensive Income (Loss) - Reclassification Out of Accumulated Other Comprehensive Income (Loss) (Detail) - USD ($) $ in Thousands	3 Months Ended		6 Months Ended
	Jun. 30, 2022	Jun. 30, 2021	Jun. 30, 2022	Jun. 30, 2021
Reclassification Adjustment Out Of Accumulated Other Comprehensive Income [Line Items]
Net realized gains on investments	$ 1,079	$ 1,179	$ 1,817	$ 1,498
Income before income taxes	7,123	29,171	28,545	52,796
Income tax expense	(991)	(5,404)	(5,082)	(9,717)
Net income	6,132	23,767	23,463	43,079
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 on investments	865	1,580	894	1,976
Income before income taxes	865	1,580	894	1,976
Income tax expense	(182)	(332)	(188)	(415)
Net income	$ 683	$ 1,248	$ 706	$ 1,561