Investments (Realized Investment Gains Losses, Net) (Details) - USD ($) $ in Thousands	3 Months Ended
	Mar. 31, 2020	Mar. 31, 2019
Schedule Of Gain Loss On Investments [Line Items]
Realized investment gains (losses), net	$ 89,895	$ (48,635)
Fixed maturities
Schedule Of Gain Loss On Investments [Line Items]
Realized investment gains (losses), net	(2,675)	(4,184)
Commercial mortgage and other loans
Schedule Of Gain Loss On Investments [Line Items]
Realized investment gains (losses), net	(188)	7
LPs/LLCs
Schedule Of Gain Loss On Investments [Line Items]
Realized investment gains (losses), net	(315)	12
Derivatives
Schedule Of Gain Loss On Investments [Line Items]
Realized investment gains (losses), net	93,457	(44,477)
Short-term investments and cash equivalents
Schedule Of Gain Loss On Investments [Line Items]
Realized investment gains (losses), net	$ (384)	$ 7