Investments (Net Investment Income) (Details) - USD ($) $ in Thousands	3 Months Ended		9 Months Ended
	Sep. 30, 2015	Sep. 30, 2014	Sep. 30, 2015	Sep. 30, 2014
Schedule of Investment Income, Reported Amounts, by Category [Line Items]
Gross investment income	$ 108,029	$ 106,015	$ 323,996	$ 317,239
Less: investment expenses	(5,814)	(5,061)	(16,875)	(14,588)
Net investment income	102,215	100,954	307,121	302,651
Fixed maturities, available-for-sale
Schedule of Investment Income, Reported Amounts, by Category [Line Items]
Gross investment income	68,428	65,656	198,912	197,684
Equity securities, available-for-sale
Schedule of Investment Income, Reported Amounts, by Category [Line Items]
Gross investment income	0	0	1	1
Trading account assets
Schedule of Investment Income, Reported Amounts, by Category [Line Items]
Gross investment income	774	206	2,021	603
Commercial mortgage and other loans
Schedule of Investment Income, Reported Amounts, by Category [Line Items]
Gross investment income	21,891	20,963	64,427	61,684
Policy loans
Schedule of Investment Income, Reported Amounts, by Category [Line Items]
Gross investment income	16,155	15,634	46,641	45,432
Short-term investments and cash equivalents
Schedule of Investment Income, Reported Amounts, by Category [Line Items]
Gross investment income	203	89	662	349
Other long-term investments
Schedule of Investment Income, Reported Amounts, by Category [Line Items]
Gross investment income	$ 578	$ 3,467	$ 11,332	$ 11,486