Investments - Schedule of Analysis of Investment Operations (Detail) - USD ($) $ in Thousands	12 Months Ended
Dec. 31, 2021	Dec. 31, 2020	Dec. 31, 2019
Net Investment Income [Line Items]
Investment income, gross	$ 973,601	$ 944,894	$ 926,504
Less investment expense	(21,154)	(17,832)	(16,045)
Net investment income	952,447	927,062	910,459
Fixed maturities available for sale
Net Investment Income [Line Items]
Investment income, gross	892,421	873,352	864,280
Policy loans
Net Investment Income [Line Items]
Investment income, gross	45,318	44,801	43,434
Other long-term investments
Net Investment Income [Line Items]
Investment income, gross	35,838	26,196	16,198
Short-term investments
Net Investment Income [Line Items]
Investment income, gross	24	545	2,592
Fair value option
Net Investment Income [Line Items]
Net investment income	$ 26,700	$ 15,300	$ 5,600

Amount, before investment expense, of income earned from investments in securities and real estate. Includes, but is not limited to, real estate investment, policy loans, dividends, and interest. Excludes realized gain (loss) on investments.

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Amount of expenses related to the generation of investment income.

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Amount, after investment expense, of income earned from investments in securities and real estate. Includes, but is not limited to, real estate investment, policy loans, dividends, and interest. Excludes realized gain (loss) on investments.

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