Amounts of Gross Realized Capital Gains and Gross Realized Capital Losses (Detail) - USD ($) $ in Thousands	3 Months Ended
	Mar. 31, 2021	Mar. 31, 2020
Investments Debt And Equity Securities [Abstract]
Gross realized capital gains	$ 20,900	$ 59,000	[1]
Gross realized capital losses	(8,000)	(46,000)	[2]
Net realized capital gains	$ 12,931	$ 13,026

[1] Gross realized capital gains in the three months ended March 31, 2020 include a $5.0 million realized gain from a reduction of certain contingent consideration liabilities at the PCT-level in connection with its acquisition of a provider of high-performance solid carbide end mills in June 2019.

[2] Gross realized capital losses in the three months ended March 31, 2020 include (i) impairment charges of $30.0 million from write-downs of SORC oil field assets prior to SORC’s December 31, 2020 sale; and (ii) a $7.1 million realized loss as a result of an early redemption of debt (see 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).