Investments (Net Investment Income) (Details) - USD ($) $ in Thousands	3 Months Ended		6 Months Ended
	Jun. 30, 2015	Jun. 30, 2014	Jun. 30, 2015	Jun. 30, 2014
Schedule of Investment Income, Reported Amounts, by Category [Line Items]
Gross investment income	$ 107,159	$ 108,113	$ 215,967	$ 211,224
Less: investment expenses	(5,673)	(4,893)	(11,061)	(9,527)
Net investment income	101,486	103,220	204,906	201,697
Fixed maturities, available-for-sale
Schedule of Investment Income, Reported Amounts, by Category [Line Items]
Gross investment income	66,546	66,293	130,484	132,028
Equity securities, available-for-sale
Schedule of Investment Income, Reported Amounts, by Category [Line Items]
Gross investment income	0	1	1	1
Trading account assets
Schedule of Investment Income, Reported Amounts, by Category [Line Items]
Gross investment income	735	201	1,247	397
Commercial mortgage and other loans
Schedule of Investment Income, Reported Amounts, by Category [Line Items]
Gross investment income	21,639	20,891	42,536	40,721
Policy loans
Schedule of Investment Income, Reported Amounts, by Category [Line Items]
Gross investment income	15,371	15,072	30,486	29,798
Short-term investments and cash equivalents
Schedule of Investment Income, Reported Amounts, by Category [Line Items]
Gross investment income	184	103	459	260
Other long-term investments
Schedule of Investment Income, Reported Amounts, by Category [Line Items]
Gross investment income	$ 2,684	$ 5,552	$ 10,754	$ 8,019