Investments - Realized Gain (Loss) on Investments (Detail) - USD ($) $ in Thousands	3 Months Ended		9 Months Ended
	Sep. 30, 2020	Sep. 30, 2019	Sep. 30, 2020	Sep. 30, 2019
Investments, Debt and Equity Securities [Abstract]
Realized investment gains (losses) - sales and other	$ (38,608)	$ 12,430	$ (27,746)	$ 18,337
Provision for credit losses	28,332	0	(4,387)	0
Fair value option—change in fair value	12,053	(487)	(6,798)	197
Other investments	358	0	10,179	(108)
Realized gains (losses) from investments	2,135	11,943	(28,752)	18,426
Realized loss on redemption of debt	(634)	0	(634)	0
Realized gains (losses)	1,501	11,943	(29,386)	18,426
Applicable tax	463	(2,508)	6,949	(3,869)
Realized gains (losses), net of tax	1,964	9,435	(22,437)	14,557
Exchanges of fixed maturities	65,800	43,700	152,100	161,000
Exchanges of fixed maturities, net realized gains	$ 0	$ 11,800	$ 7,900	$ 20,100