Investments (Held To Maturity Securities Allowance for Credit Losses by Credit Rating) (Details) - USD ($) $ in Thousands	Sep. 30, 2020	Jun. 30, 2020	Jan. 01, 2020	Dec. 31, 2019
Debt Securities, Held-to-maturity, Credit Quality Indicator [Line Items]
Amortized Cost	$ 6,827,139			$ 7,106,245
Allowance for Credit Losses	(5,086)	$ (4,940)	$ (3,300)	0
Totals	6,822,053			$ 7,106,245
AAA
Debt Securities, Held-to-maturity, Credit Quality Indicator [Line Items]
Amortized Cost	95,861
Allowance for Credit Losses	0
Totals	95,861
AA
Debt Securities, Held-to-maturity, Credit Quality Indicator [Line Items]
Amortized Cost	1,639,976
Allowance for Credit Losses	(379)
Totals	1,639,597
A
Debt Securities, Held-to-maturity, Credit Quality Indicator [Line Items]
Amortized Cost	2,224,126
Allowance for Credit Losses	(939)
Totals	2,223,187
BBB
Debt Securities, Held-to-maturity, Credit Quality Indicator [Line Items]
Amortized Cost	2,737,258
Allowance for Credit Losses	(3,292)
Totals	2,733,966
BB and other below investment
Debt Securities, Held-to-maturity, Credit Quality Indicator [Line Items]
Amortized Cost	129,918
Allowance for Credit Losses	(476)
Totals	$ 129,442