Investments - Schedule of Analysis of Investment Operations (Detail) - USD ($) $ in Thousands	3 Months Ended		9 Months Ended
	Sep. 30, 2022	Sep. 30, 2021	Sep. 30, 2022	Sep. 30, 2021
Net Investment Income [Line Items]
Investment income, gross	$ 251,291	$ 244,063	$ 749,876	$ 728,704
Less investment expense	(5,666)	(5,088)	(16,775)	(15,601)
Net investment income	$ 245,625	238,975	$ 733,101	713,103
Percentage change in investment income, gross	3.00%		3.00%
Percentage change in investment expense	11.00%		8.00%
Percentage change in net investment income	3.00%		3.00%
Investment distribution	$ 8,400	7,100	$ 27,700	19,400
Fixed maturities available for sale
Net Investment Income [Line Items]
Investment income, gross	$ 227,673	223,287	$ 679,710	668,284
Percentage change in investment income, gross	2.00%		2.00%
Policy loans
Net Investment Income [Line Items]
Investment income, gross	$ 11,716	11,376	$ 34,724	33,968
Percentage change in investment income, gross	3.00%		2.00%
Other long-term investments
Net Investment Income [Line Items]
Investment income, gross	$ 10,933	9,390	$ 34,349	26,432
Percentage change in investment income, gross	16.00%		30.00%
Short-term investments
Net Investment Income [Line Items]
Investment income, gross	$ 969	$ 10	$ 1,093	$ 20
Percentage change in investment income, gross