Investments - Schedule of Analysis of Investment Operations (Details) - USD ($) $ in Thousands	3 Months Ended
Mar. 31, 2019	Mar. 31, 2018
Net Investment Income [Line Items]
Investment income, gross	$ 230,606	$ 221,985
Less investment expense	(3,933)	(3,901)
Net investment income	226,673	218,084
Fixed maturities available for sale [Member]
Net Investment Income [Line Items]
Investment income, gross	215,763	208,542
Policy loans [Member]
Net Investment Income [Line Items]
Investment income, gross	10,636	10,198
Other long-term investments [Member]
Net Investment Income [Line Items]
Investment income, gross	3,388	2,854
Short-term investments [Member]
Net Investment Income [Line Items]
Investment income, gross	$ 819	$ 391

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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