Investments (Investment Income Net of Related Expenses) (Details) - USD ($) $ in Thousands	3 Months Ended
	Mar. 31, 2019	Mar. 31, 2018
Major Categories Of Investment Income Net of Expenses [Line Items]
Investment revenue	$ 600,874	$ 538,382
Investment expense	(20,997)	(22,053)
Investment income, net of related expenses	579,877	516,329
Available-for-sale Securities [Member]
Major Categories Of Investment Income Net of Expenses [Line Items]
Investment revenue	415,087	369,203
Equity Securities [Member]
Major Categories Of Investment Income Net of Expenses [Line Items]
Investment revenue	1,246	1,682
Mortgage Loans on Real Estate [Member]
Major Categories Of Investment Income Net of Expenses [Line Items]
Investment revenue	59,562	50,199
Policy loans
Major Categories Of Investment Income Net of Expenses [Line Items]
Investment revenue	14,109	14,780
Funds withheld at interest
Major Categories Of Investment Income Net of Expenses [Line Items]
Investment revenue	61,734	75,445
Short-term Investments [Member]
Major Categories Of Investment Income Net of Expenses [Line Items]
Investment revenue	6,900	3,245
Other invested assets
Major Categories Of Investment Income Net of Expenses [Line Items]
Investment revenue	$ 42,236	$ 23,828