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	$ 425,180	$ (17,321)	$ 274,418
Fixed Maturities | Available-for-sale Securities | OTTI
Gain (Loss) on Securities [Line Items]
Net Unrealized Gains (Losses) on Investments	1,568	(689)	1,609
Fixed Maturities | Available-for-sale Securities | All other
Gain (Loss) on Securities [Line Items]
Net Unrealized Gains (Losses) on Investments	397,136	(44,619)	279,749
Equity securities | Available-for-sale Securities
Gain (Loss) on Securities [Line Items]
Net Unrealized Gains (Losses) on Investments	0	0	2,368
Derivatives designated as cash flow hedges
Gain (Loss) on Securities [Line Items]
Net Unrealized Gains (Losses) on Investments	26,126	22,122	(17,678)
Affiliated notes
Gain (Loss) on Securities [Line Items]
Net Unrealized Gains (Losses) on Investments	4,715	810	4,782
Other Investments
Gain (Loss) on Securities [Line Items]
Net Unrealized Gains (Losses) on Investments	$ (4,365)	$ 5,055	$ 3,588