Investments - Realized Gain (Loss) on Investments (Detail) - USD ($) $ in Thousands		3 Months Ended		9 Months Ended
	Jul. 15, 2021	Sep. 30, 2021	Sep. 30, 2020	Sep. 30, 2021	Sep. 30, 2020
Investments, Debt and Equity Securities [Abstract]
Realized investment gains (losses) - sales and other		$ 16,269	$ (38,608)	$ 32,578	$ (27,746)
Provision for credit losses		0	28,332	3,346	(4,387)
Fair value option—change in fair value		1,585	12,053	14,013	(6,798)
Other investments		1,935	358	6,663	10,179
Realized gains (losses) from investments		19,789	2,135	56,600	(28,752)
Realized loss—redemption of debt	$ (9,300)	(9,314)	(634)	(9,314)	(634)
Realized gains (losses)		10,475	1,501	47,286	(29,386)
Applicable tax		(2,200)	463	(9,930)	6,949
Realized gains (losses), net of tax		8,275	1,964	37,356	(22,437)
Exchanges of fixed maturities		0	65,800	108,300	152,100
Exchanges of fixed maturities, net realized gains		$ 0	$ 0	$ 25,200	$ 7,900