Reclassifications of Accumulated Other Comprehensive Income (Detail) - USD ($) $ in Thousands		12 Months Ended
		Dec. 31, 2020	Dec. 31, 2019	Dec. 31, 2018
Reclassification Adjustment out of Accumulated Other Comprehensive Income [Line Items]
Net realized capital gains		$ (3,098)	$ 6,551	$ 3,241
Change in allowance for credit losses on available for sale securities		8,029
Change in allowance for credit losses on available for sale securities			19,660	1,328
Income taxes		30,734	233,435	$ (15,062)
Unrealized Appreciation of Investments
Reclassification Adjustment out of Accumulated Other Comprehensive Income [Line Items]
Total reclassifications		(33,100)	(20,400)
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]	(49,900)	(45,500)
Change in allowance for credit losses on available for sale securities		8,000
Change in allowance for credit losses on available for sale securities			19,700
Income taxes		$ 8,800	$ 5,400

[1] For 2020, excludes: (i) the 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. For 2019, excludes: (i) a $38.4 million loss on the Put Option; and (ii) a $13.6 million loss from the December 2019 sale from a privately held investment accounted for under the equity method. See Note 4(e) for additional information.