Investments (Net Investment Income) (Details) - USD ($) $ in Thousands	3 Months Ended		6 Months Ended
	Jun. 30, 2016	Jun. 30, 2015	Jun. 30, 2016	Jun. 30, 2015
Schedule of Investment Income, Reported Amounts, by Category [Line Items]
Gross investment income	$ 87,445	$ 35,448	$ 121,841	$ 74,437
Less: investment expenses	(2,625)	(1,392)	(4,011)	(2,792)
Net investment income	84,820	34,056	117,830	71,645
Fixed maturities, available-for-sale
Schedule of Investment Income, Reported Amounts, by Category [Line Items]
Gross investment income	64,314	28,861	93,384	59,643
Trading account assets
Schedule of Investment Income, Reported Amounts, by Category [Line Items]
Gross investment income	1,063	29	1,065	31
Commercial mortgage and other loans
Schedule of Investment Income, Reported Amounts, by Category [Line Items]
Gross investment income	11,480	5,008	16,376	10,244
Policy loans
Schedule of Investment Income, Reported Amounts, by Category [Line Items]
Gross investment income	222	258	332	388
Short-term investments
Schedule of Investment Income, Reported Amounts, by Category [Line Items]
Gross investment income	7,493	57	7,697	101
Other long-term investments
Schedule of Investment Income, Reported Amounts, by Category [Line Items]
Gross investment income	$ 2,873	$ 1,235	$ 2,987	$ 4,030