Investments - Schedule of Analysis of Investment Operations (Detail) - USD ($) $ in Thousands	3 Months Ended		6 Months Ended
	Jun. 30, 2022	Jun. 30, 2021	Jun. 30, 2022	Jun. 30, 2021
Net Investment Income [Line Items]
Investment income, gross	$ 249,158	$ 243,488	$ 498,585	$ 484,641
Less investment expense	(5,516)	(5,180)	(11,109)	(10,513)
Net investment income	$ 243,642	238,308	$ 487,476	474,128
Percentage change in investment income, gross	2.00%		3.00%
Percentage change in investment expense	6.00%		6.00%
Percentage change in net investment income	2.00%		3.00%
Investment distribution	$ 8,600	6,500	$ 19,300	12,300
Fixed maturities available for sale
Net Investment Income [Line Items]
Investment income, gross	$ 226,753	223,278	$ 452,037	444,997
Percentage change in investment income, gross	2.00%		2.00%
Policy loans
Net Investment Income [Line Items]
Investment income, gross	$ 11,580	11,324	$ 23,008	22,592
Percentage change in investment income, gross	2.00%		2.00%
Other long-term investments
Net Investment Income [Line Items]
Investment income, gross	$ 10,703	8,880	$ 23,416	17,042
Percentage change in investment income, gross	21.00%		37.00%
Short-term investments
Net Investment Income [Line Items]
Investment income, gross	$ 122	$ 6	$ 124	$ 10
Percentage change in investment income, gross	1933.00%		1140.00%