Investments (Net Unrealized Gains Losses on Investments by Asset Class) (Details) - USD ($) $ in Thousands	Jun. 30, 2021	Dec. 31, 2020
Gain (Loss) on Securities [Line Items]
Net Unrealized Gains (Losses) on Investments	$ 663,756	$ 849,349
Fixed maturities | Available-for-sale | With an allowance
Gain (Loss) on Securities [Line Items]
Net Unrealized Gains (Losses) on Investments	68	0
Fixed maturities | Available-for-sale | Without an allowance
Gain (Loss) on Securities [Line Items]
Net Unrealized Gains (Losses) on Investments	648,019	857,599
Derivatives designated as cash flow hedges
Gain (Loss) on Securities [Line Items]
Net Unrealized Gains (Losses) on Investments	12,248	(8,112)
Affiliated notes
Gain (Loss) on Securities [Line Items]
Net Unrealized Gains (Losses) on Investments	2,603	4,024
Other investments
Gain (Loss) on Securities [Line Items]
Net Unrealized Gains (Losses) on Investments	$ 818	$ (4,162)