Investments (Investment Income Net of Related Expenses) (Details) - USD ($) $ in Thousands	3 Months Ended		9 Months Ended
	Sep. 30, 2016	Sep. 30, 2015	Sep. 30, 2016	Sep. 30, 2015
Major Categories Of Investment Income Net of Expenses [Line Items]
Investment revenue	$ 507,781	$ 406,052	$ 1,468,130	$ 1,317,332
Investment expense	(18,054)	(16,455)	(53,471)	(50,305)
Investment income, net of related expenses	489,727	389,597	1,414,659	1,267,027
Available-for-sale Securities [Member]
Major Categories Of Investment Income Net of Expenses [Line Items]
Investment revenue	325,089	298,376	961,096	871,936
Mortgage Loans on Real Estate [Member]
Major Categories Of Investment Income Net of Expenses [Line Items]
Investment revenue	39,802	36,547	121,494	108,440
Policy loans
Major Categories Of Investment Income Net of Expenses [Line Items]
Investment revenue	15,391	16,475	47,897	46,763
Funds withheld at interest
Major Categories Of Investment Income Net of Expenses [Line Items]
Investment revenue	104,609	40,382	273,482	239,967
Short-term Investments [Member]
Major Categories Of Investment Income Net of Expenses [Line Items]
Investment revenue	952	576	2,912	2,085
Other invested assets
Major Categories Of Investment Income Net of Expenses [Line Items]
Investment revenue	$ 21,938	$ 13,696	$ 61,249	$ 48,141