Investments (Net Investment Income) (Details) - USD ($) $ in Thousands	3 Months Ended
	Mar. 31, 2018	Mar. 31, 2017
Schedule of Investment Income, Reported Amounts, by Category [Line Items]
Gross investment income	$ 82,494	$ 94,777
Less: investment expenses	(4,579)	(5,162)
Net investment income	77,915	89,615
Equity securities, at fair value
Schedule of Investment Income, Reported Amounts, by Category [Line Items]
Gross investment income	221	221
Commercial mortgage and other loans
Schedule of Investment Income, Reported Amounts, by Category [Line Items]
Gross investment income	12,405	13,116
Policy loans
Schedule of Investment Income, Reported Amounts, by Category [Line Items]
Gross investment income	15,904	15,628
Short-term investments and cash equivalents
Schedule of Investment Income, Reported Amounts, by Category [Line Items]
Gross investment income	323	187
Other invested assets
Schedule of Investment Income, Reported Amounts, by Category [Line Items]
Gross investment income	115	6,379
Available-for-sale | Fixed maturities
Schedule of Investment Income, Reported Amounts, by Category [Line Items]
Gross investment income	53,260	59,067
Trading | Fixed maturities
Schedule of Investment Income, Reported Amounts, by Category [Line Items]
Gross investment income	$ 266	$ 179