Investments (Realized Investment Gains Losses, Net) (Details) - USD ($) $ in Thousands	3 Months Ended		9 Months Ended
	Sep. 30, 2019	Sep. 30, 2018	Sep. 30, 2019	Sep. 30, 2018
Schedule Of Gain Loss On Investments [Line Items]
Realized investment gains (losses), net	$ 39,584	$ (49,423)	$ (61,301)	$ (135,355)
Fixed maturities
Schedule Of Gain Loss On Investments [Line Items]
Realized investment gains (losses), net	27,418	(1,048)	20,745	(5,175)
Commercial mortgage and other loans
Schedule Of Gain Loss On Investments [Line Items]
Realized investment gains (losses), net	54	16	160	22
LPs/LLCs
Schedule Of Gain Loss On Investments [Line Items]
Realized investment gains (losses), net	0	0	12	849
Derivatives
Schedule Of Gain Loss On Investments [Line Items]
Realized investment gains (losses), net	12,129	(48,393)	(82,194)	(131,034)
Short-term investments and cash equivalents
Schedule Of Gain Loss On Investments [Line Items]
Realized investment gains (losses), net	$ (17)	$ 2	$ (24)	$ (17)