Investments (Realized Investment Gains Losses, Net) (Details) - USD ($) $ in Thousands	3 Months Ended
	Mar. 31, 2018	Mar. 31, 2017
Schedule Of Gain Loss On Investments [Line Items]
Realized investment gains (losses), net	$ (49,042)	$ (32,579)
Fixed maturities
Schedule Of Gain Loss On Investments [Line Items]
Realized investment gains (losses), net	(809)	(4,030)
Equity securities
Schedule Of Gain Loss On Investments [Line Items]
Realized investment gains (losses), net	0	(114)
Commercial mortgage and other loans
Schedule Of Gain Loss On Investments [Line Items]
Realized investment gains (losses), net	131	(139)
LPS/LLCS
Schedule Of Gain Loss On Investments [Line Items]
Realized investment gains (losses), net	847	(73)
Derivatives
Schedule Of Gain Loss On Investments [Line Items]
Realized investment gains (losses), net	(49,193)	(28,217)
Short-term investments and cash equivalents
Schedule Of Gain Loss On Investments [Line Items]
Realized investment gains (losses), net	$ (18)	$ (6)