Investments (Net Unrealized Gains Losses on Investments by Asset Class) (Details) - USD ($) $ in Thousands	Mar. 31, 2019	Dec. 31, 2018
Gain (Loss) on Securities [Line Items]
Net unrealized gains (losses) on investments	$ (36,160)	$ (416,909)
Fixed maturities | Available-for-sale | OTTI
Gain (Loss) on Securities [Line Items]
Net unrealized gains (losses) on investments	3,283	(3,334)
Fixed maturities | Available-for-sale | All other
Gain (Loss) on Securities [Line Items]
Net unrealized gains (losses) on investments	(38,980)	(411,458)
Derivatives designated as cash flow hedges
Gain (Loss) on Securities [Line Items]
Net unrealized gains (losses) on investments	(2,184)	(3,849)
Affiliated notes
Gain (Loss) on Securities [Line Items]
Net unrealized gains (losses) on investments	646	658
Other investments
Gain (Loss) on Securities [Line Items]
Net unrealized gains (losses) on investments	$ 1,075	$ 1,074