Investments (Investment Income Net of Related Expenses) (Details) - USD ($) $ in Thousands	3 Months Ended		6 Months Ended
	Jun. 30, 2015	Jun. 30, 2014	Jun. 30, 2015	Jun. 30, 2014
Major Categories Of Investment Income Net of Expenses [Line Items]
Investment revenue	$ 467,718	$ 424,740	$ 911,280	$ 843,437
Investment expense	(17,179)	(14,133)	(33,850)	(28,455)
Investment income, net of related expenses	450,539	410,607	877,430	814,982
Available-for-sale Securities [Member]
Major Categories Of Investment Income Net of Expenses [Line Items]
Investment revenue	303,792	253,456	573,560	497,418
Mortgage Loans on Real Estate [Member]
Major Categories Of Investment Income Net of Expenses [Line Items]
Investment revenue	37,121	30,373	71,893	63,465
Policy loans
Major Categories Of Investment Income Net of Expenses [Line Items]
Investment revenue	16,248	13,751	30,288	27,189
Funds withheld at interest
Major Categories Of Investment Income Net of Expenses [Line Items]
Investment revenue	87,325	108,059	199,585	220,798
Short-term Investments [Member]
Major Categories Of Investment Income Net of Expenses [Line Items]
Investment revenue	814	80	1,509	1,045
Other invested assets
Major Categories Of Investment Income Net of Expenses [Line Items]
Investment revenue	$ 22,418	$ 19,021	$ 34,445	$ 33,522