Investments (Net Investment Income) (Details) - USD ($) $ in Thousands	3 Months Ended
Mar. 31, 2019	Mar. 31, 2018
Schedule of Investment Income, Reported Amounts, by Category [Line Items]
Gross investment income	$ 129,022	$ 100,505
Less: investment expenses	(3,953)	(3,794)
Net investment income	125,069	96,711
Equity securities
Schedule of Investment Income, Reported Amounts, by Category [Line Items]
Gross investment income	73	68
Commercial mortgage and other loans
Schedule of Investment Income, Reported Amounts, by Category [Line Items]
Gross investment income	11,732	13,493
Policy loans
Schedule of Investment Income, Reported Amounts, by Category [Line Items]
Gross investment income	59	135
Short-term investments and cash equivalents
Schedule of Investment Income, Reported Amounts, by Category [Line Items]
Gross investment income	13,740	6,527
Other invested assets
Schedule of Investment Income, Reported Amounts, by Category [Line Items]
Gross investment income	8,842	3,630
Available-for-sale \| Fixed maturities
Schedule of Investment Income, Reported Amounts, by Category [Line Items]
Gross investment income	92,211	76,051
Trading \| Fixed maturities
Schedule of Investment Income, Reported Amounts, by Category [Line Items]
Gross investment income	$ 2,365	$ 601

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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