Reclassifications of Accumulated Other Comprehensive Income (Loss) (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 capital gains	$ 10,003	$ (12,931)
Change in allowance for credit losses on available for sale securities	582	(1,972)
Income taxes	45,082	58,867
Unrealized Appreciation of Investments
Reclassification Adjustment out of Accumulated Other Comprehensive Income [Line Items]
Total reclassifications	8,400	(11,800)
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	10,000	(12,900)
Change in allowance for credit losses on available for sale securities	600	(2,000)
Income taxes	$ (2,200)	$ 3,100