Investments (Net Unrealized Gains Losses on Investments by Asset Class) (Details) - USD ($) $ in Thousands	Jun. 30, 2020	Dec. 31, 2019
Gain (Loss) on Securities [Line Items]
Net Unrealized Gains (Losses) on Investments	$ 656,099	$ 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	(874)
Fixed maturities | Available-for-sale | Without an allowance
Gain (Loss) on Securities [Line Items]
Net Unrealized Gains (Losses) on Investments	561,468
Derivatives designated as cash flow hedges
Gain (Loss) on Securities [Line Items]
Net Unrealized Gains (Losses) on Investments	93,867	26,126
Affiliated notes
Gain (Loss) on Securities [Line Items]
Net Unrealized Gains (Losses) on Investments	6,029	4,715
Other investments
Gain (Loss) on Securities [Line Items]
Net Unrealized Gains (Losses) on Investments	$ (4,391)	$ (4,365)