Reclassifications of Accumulated Other Comprehensive Income (Loss) (Detail) - USD ($) $ in Thousands		3 Months Ended
		Mar. 31, 2021	Mar. 31, 2020
Reclassification Adjustment out of Accumulated Other Comprehensive Income [Line Items]
Net realized capital gains		$ (12,931)	$ (13,026)
Change in allowance for credit losses on available for sale securities		(1,972)	31,375
Income taxes		58,867	(104,720)
Unrealized Appreciation of Investments
Reclassification Adjustment out of Accumulated Other Comprehensive Income [Line Items]
Total reclassifications		(11,800)	(10,900)
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]	(12,900)	(45,100)
Change in allowance for credit losses on available for sale securities		(2,000)	31,400
Income taxes		$ 3,100	$ 2,800

[1] For the three months ended March 31, 2020, excludes: (i) a $7.1 million realized loss as a result of an early redemption of debt (Note 8 to Notes to Consolidated Financial Statements set forth in Part II, Item 8, “Financial Statements and Supplementary Data” of the 2020 Form 10-K for further information); (ii) $30.0 million of impairment charges from a write-down of SORC oil field assets; and (iii) a $5.0 million realized gain resulting from a reduction of certain PCT contingent consideration liabilities (see Note 3(e) of this Form 10-Q for additional information).