Reclassifications of Accumulated Other Comprehensive Income (Loss) (Detail) - USD ($) $ in Thousands		3 Months Ended
		Mar. 31, 2020	Mar. 31, 2019
Reclassification Adjustment out of Accumulated Other Comprehensive Income [Line Items]
Net realized capital gains		$ (13,026)	$ (4,442)
Credit losses for available for sale securities		31,375
Credit losses for available for sale securities			10,020
Income taxes		(104,720)	108,512
Unrealized Appreciation of Investments
Reclassification Adjustment out of Accumulated Other Comprehensive Income [Line Items]
Total reclassifications		(10,900)	4,400
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]	(45,100)	(4,400)
Credit losses for available for sale securities		31,400
Credit losses for available for sale securities			10,000
Income taxes		$ 2,800	$ (1,200)

[1] For the three months ended March 31, 2020, excludes a $7.1 million realized loss as a result of an early redemption of debt (see Note 11(a) of this Form 10-Q for further information), a $30.0 million impairment charge from a write-down of certain SORC assets and a $5.0 million realized gain from a reduction of certain contingent consideration liabilities (see Note 3(e) of this Form 10-Q for additional information).