Investments - Realized Gain (Loss) on Investments (Detail) - USD ($) $ in Thousands	3 Months Ended		6 Months Ended
	Jun. 30, 2020	Jun. 30, 2019	Jun. 30, 2020	Jun. 30, 2019
Investments, Debt and Equity Securities [Abstract]
Realized investment gains (losses) - sales and other	$ 5,928	$ 2,237	$ 10,862	$ 5,907
Provision for credit losses	(865)	0	(32,719)	0
Fair value option—change in fair value	(19,434)	2,869	(18,851)	684
Other investments	9,581	48	9,821	(108)
Realized gains (losses) from investments	(4,790)	5,154	(30,887)	6,483
Applicable tax	1,006	(1,082)	6,486	(1,361)
Realized gains (losses), net of tax	(3,784)	4,072	(24,401)	5,122
Exchanges of fixed maturities	80,400	48,300	86,300	117,200
Exchanges of fixed maturities, net realized gains	$ 7,900	$ 2,500	$ 7,900	$ 8,300