Investments (Net Unrealized Gains Losses on Investments by Asset Class) (Details) - USD ($) $ in Thousands	Dec. 31, 2019	Dec. 31, 2018	Dec. 31, 2017
Gain (Loss) on Securities [Line Items]
Net Unrealized Gains (Losses) on Investments	$ 736,930	$ (416,909)	$ (59,412)
Fixed maturities | Available-for-sale | OTTI
Gain (Loss) on Securities [Line Items]
Net Unrealized Gains (Losses) on Investments	14,309	(3,334)	12,311
Fixed maturities | Available-for-sale | All other
Gain (Loss) on Securities [Line Items]
Net Unrealized Gains (Losses) on Investments	722,310	(411,458)	(46,791)
Equity securities | Available-for-sale
Gain (Loss) on Securities [Line Items]
Net Unrealized Gains (Losses) on Investments	0	0	4
Derivatives designated as cash flow hedges
Gain (Loss) on Securities [Line Items]
Net Unrealized Gains (Losses) on Investments	(287)	(3,849)	(25,851)
Affiliated notes
Gain (Loss) on Securities [Line Items]
Net Unrealized Gains (Losses) on Investments	598	658	829
Other Investments
Gain (Loss) on Securities [Line Items]
Net Unrealized Gains (Losses) on Investments	$ 0	$ 1,074	$ 86