Investments (Net Investment Income) (Details) - USD ($) $ in Thousands	12 Months Ended
	Dec. 31, 2018	Dec. 31, 2017	Dec. 31, 2016
Schedule of Investment Income, Reported Amounts, by Category [Line Items]
Gross investment income	$ 417,743	$ 438,873	$ 349,662
Less: investment expenses	(14,935)	(16,064)	(11,292)
Net investment income(1)	402,808	422,809	338,370
Equity securities
Schedule of Investment Income, Reported Amounts, by Category [Line Items]
Gross investment income	678	567	330
Commercial mortgage and other loans
Schedule of Investment Income, Reported Amounts, by Category [Line Items]
Gross investment income	51,040	48,598	40,258
Policy loans
Schedule of Investment Income, Reported Amounts, by Category [Line Items]
Gross investment income	737	1,069	444
Short-term investments and cash equivalents
Schedule of Investment Income, Reported Amounts, by Category [Line Items]
Gross investment income	28,645	31,505	26,831
Other invested assets
Schedule of Investment Income, Reported Amounts, by Category [Line Items]
Gross investment income	13,733	20,626	29,160
Available-for-sale | Fixed maturities
Schedule of Investment Income, Reported Amounts, by Category [Line Items]
Gross investment income	317,726	332,148	249,496
Trading | Fixed maturities
Schedule of Investment Income, Reported Amounts, by Category [Line Items]
Gross investment income	$ 5,184	$ 4,360	$ 3,143