Investments (Realized Investment Gains Losses, Net) (Details) - USD ($) $ in Thousands	3 Months Ended		9 Months Ended
	Sep. 30, 2018	Sep. 30, 2017	Sep. 30, 2018	Sep. 30, 2017
Schedule Of Gain Loss On Investments [Line Items]
Realized investment gains (losses), net	$ (49,423)	$ (275,186)	$ (135,355)	$ (31,175)
Fixed maturities
Schedule Of Gain Loss On Investments [Line Items]
Realized investment gains (losses), net	(1,048)	28,594	(5,175)	28,794
Equity securities
Schedule Of Gain Loss On Investments [Line Items]
Realized investment gains (losses), net	0	0	0	(125)
Commercial mortgage and other loans
Schedule Of Gain Loss On Investments [Line Items]
Realized investment gains (losses), net	16	74	22	(414)
LPS/LLCS
Schedule Of Gain Loss On Investments [Line Items]
Realized investment gains (losses), net	0	5	849	(96)
Derivatives
Schedule Of Gain Loss On Investments [Line Items]
Realized investment gains (losses), net	(48,393)	(303,850)	(131,034)	(59,319)
Short-term investments and cash equivalents
Schedule Of Gain Loss On Investments [Line Items]
Realized investment gains (losses), net	$ 2	$ (9)	$ (17)	$ (15)