Investments (Net Unrealized Gains Losses on Investments by Asset Class) (Details) - USD ($) $ in Thousands	Sep. 30, 2020	Dec. 31, 2019
Gain (Loss) on Securities [Line Items]
Net Unrealized Gains (Losses) on Investments	$ 713,070	$ 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	(479)
Fixed maturities | Available-for-sale | Without an allowance
Gain (Loss) on Securities [Line Items]
Net Unrealized Gains (Losses) on Investments	659,038
Derivatives designated as cash flow hedges
Gain (Loss) on Securities [Line Items]
Net Unrealized Gains (Losses) on Investments	54,211	26,126
Affiliated notes
Gain (Loss) on Securities [Line Items]
Net Unrealized Gains (Losses) on Investments	4,701	4,715
Other investments
Gain (Loss) on Securities [Line Items]
Net Unrealized Gains (Losses) on Investments	$ (4,401)	$ (4,365)