Investments - Schedule of Analysis of Investment Operations (Detail) - USD ($) $ in Thousands	3 Months Ended	6 Months Ended
Jun. 30, 2019	Jun. 30, 2018	Jun. 30, 2019	Jun. 30, 2018
Net Investment Income [Line Items]
Investment income, gross	$ 231,442	$ 222,525	$ 462,048	$ 444,510
Less investment expense	(4,017)	(3,957)	(7,950)	(7,858)
Net investment income	227,425	218,568	454,098	436,652
Fixed maturities available for sale
Net Investment Income [Line Items]
Investment income, gross	215,867	209,771	431,630	418,313
Policy loans
Net Investment Income [Line Items]
Investment income, gross	10,821	10,201	21,457	20,399
Other long-term investments
Net Investment Income [Line Items]
Investment income, gross	3,991	2,120	7,379	4,974
Short-term investments
Net Investment Income [Line Items]
Investment income, gross	$ 763	$ 433	$ 1,582	$ 824

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, 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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