Reclassifications 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 capital gains	$ (11,167)	$ (12,942)	$ (1,164)	$ (25,873)
Change in allowance for credit losses on available for sale securities	7,595	(246)	8,177	(2,218)
Income taxes	(40,033)	102,281	5,049	161,148
Unrealized Appreciation of Investments
Reclassification Adjustment out of Accumulated Other Comprehensive Income [Line Items]
Total reclassifications	(2,800)	(10,400)	5,500	(22,200)
Reclassification out of Accumulated Other Comprehensive Income | Unrealized Appreciation of Investments
Reclassification Adjustment out of Accumulated Other Comprehensive Income [Line Items]
Net realized capital gains	(11,100)	(12,900)	(1,200)	(25,900)
Change in allowance for credit losses on available for sale securities	7,600	(200)	8,200	(2,200)
Income taxes	$ 700	$ 2,700	$ (1,500)	$ 5,900