Investments (Net Unrealized Gains Losses on Investments by Asset Class) (Details) - USD ($) $ in Thousands	Mar. 31, 2020	Dec. 31, 2019
Gain (Loss) on Securities [Line Items]
Net Unrealized Gains (Losses) on Investments	$ 262,686	$ 425,180
Fixed maturities | Available-for-sale | OTTI
Gain (Loss) on Securities [Line Items]
Net Unrealized Gains (Losses) on Investments		1,568
Fixed maturities | Available-for-sale | All other
Gain (Loss) on Securities [Line Items]
Net Unrealized Gains (Losses) on Investments		397,136
Fixed maturities | Available-for-sale | With an allowance
Gain (Loss) on Securities [Line Items]
Net Unrealized Gains (Losses) on Investments	0
Fixed maturities | Available-for-sale | Without an allowance
Gain (Loss) on Securities [Line Items]
Net Unrealized Gains (Losses) on Investments	142,745
Derivatives designated as cash flow hedges
Gain (Loss) on Securities [Line Items]
Net Unrealized Gains (Losses) on Investments	124,196	26,126
Affiliated notes
Gain (Loss) on Securities [Line Items]
Net Unrealized Gains (Losses) on Investments	(437)	4,715
Other investments
Gain (Loss) on Securities [Line Items]
Net Unrealized Gains (Losses) on Investments	$ (3,818)	$ (4,365)