Investments (Investment Income Net of Related Expenses) (Details) - USD ($) $ in Thousands	3 Months Ended
	Mar. 31, 2016	Mar. 31, 2015
Major Categories Of Investment Income Net of Expenses [Line Items]
Investment revenue	$ 435,119	$ 443,562
Investment expense	(17,853)	(16,671)
Investment income, net of related expenses	417,266	426,891
Available-for-sale Securities [Member]
Major Categories Of Investment Income Net of Expenses [Line Items]
Investment revenue	312,414	269,768
Mortgage Loans on Real Estate [Member]
Major Categories Of Investment Income Net of Expenses [Line Items]
Investment revenue	39,792	34,772
Policy loans
Major Categories Of Investment Income Net of Expenses [Line Items]
Investment revenue	16,134	14,040
Funds withheld at interest
Major Categories Of Investment Income Net of Expenses [Line Items]
Investment revenue	55,980	112,260
Short-term Investments [Member]
Major Categories Of Investment Income Net of Expenses [Line Items]
Investment revenue	975	695
Other invested assets
Major Categories Of Investment Income Net of Expenses [Line Items]
Investment revenue	$ 9,824	$ 12,027