Investments (Realized Investment Gains Losses, Net) (Details) - USD ($) $ in Thousands	3 Months Ended
	Mar. 31, 2019	Mar. 31, 2018
Schedule Of Gain Loss On Investments [Line Items]
Realized investment gains (losses), net	$ (48,635)	$ (49,042)
Fixed maturities
Schedule Of Gain Loss On Investments [Line Items]
Realized investment gains (losses), net	(4,184)	(809)
Commercial mortgage and other loans
Schedule Of Gain Loss On Investments [Line Items]
Realized investment gains (losses), net	7	131
LPs/LLCs
Schedule Of Gain Loss On Investments [Line Items]
Realized investment gains (losses), net	12	847
Derivatives
Schedule Of Gain Loss On Investments [Line Items]
Realized investment gains (losses), net	(44,477)	(49,193)
Short-term investments and cash equivalents
Schedule Of Gain Loss On Investments [Line Items]
Realized investment gains (losses), net	$ 7	$ (18)