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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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INVESTMENT OPERATIONS - Summary of Major Categories of Net Investment Income (Details) - USD ($) $ in Thousands	3 Months Ended								12 Months Ended
	Dec. 31, 2018	Sep. 30, 2018	Jun. 30, 2018	Mar. 31, 2018	Dec. 31, 2017	Sep. 30, 2017	Jun. 30, 2017	Mar. 31, 2017	Dec. 31, 2018	Dec. 31, 2017	Dec. 31, 2016
Investment [Line Items]
Investment income before other investment expenses									$ 2,513,756	$ 2,080,715	$ 1,971,567
Investment expenses									30,006	29,127	29,111
Net investment income	$ 674,286	$ 672,139	$ 616,462	$ 520,863	$ 529,490	$ 507,914	$ 507,771	$ 506,413	2,483,750	2,051,588	1,942,456
Fixed maturities
Investment [Line Items]
Investment income before other investment expenses									2,051,505	1,631,565	1,552,999
Equity securities
Investment [Line Items]
Investment income before other investment expenses									35,299	39,806	38,838
Mortgage loans
Investment [Line Items]
Investment income before other investment expenses									322,207	298,387	270,749
Investment real estate
Investment [Line Items]
Investment income before other investment expenses									1,888	2,481	2,153
Short-term investments
Investment [Line Items]
Investment income before other investment expenses									$ 102,857	$ 108,476	$ 106,828