Reclassifications 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 capital gains		$ (67,493)	$ (3,098)	$ 6,551
Change in allowance for credit losses on available for sale securities		(2,077)	8,029
Income taxes		281,925	30,734	$ 233,435
Unrealized Appreciation of Investments
Reclassification Adjustment out of Accumulated Other Comprehensive Income [Line Items]
Total reclassifications		(52,500)	(33,100)
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	[1]	(64,400)	(49,900)
Change in allowance for credit losses on available for sale securities		(2,100)	8,000
Income taxes		$ 14,000	$ 8,800

[1] For 2021, excludes: the 2021 Concord Remeasurement Gain. For 2020, excludes: (i) the 2020 Concord Settlement Gain; (ii) $76.0 million of impairment charge from a write-down of SORC oil field assets; (iii) the Wilbert Remeasurement Gain; (iv) a $7.1 million realized loss as a result of an early redemption of debt; and (v) a $5.0 million realized gain resulting from a reduction of certain PCT contingent consideration liabilities. See Note 4(e) for additional information.