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Investments (Fair Value and Gross Pre-Tax Net Unrealized Loss of Securities By Length of Time) (Details) - USD ($) $ in Thousands		9 Months Ended
		Sep. 30, 2019	Dec. 31, 2018
Percent Of Securities of Amortized Cost In An Unrealized Unrecognized Loss Position		1.00%	2.00%
AFS Fixed Income Securities [Member]
AFS Fair Value, Less than 12 Months		$ 416,634	$ 2,142,433
AFS Unrealized Losses, Less than 12 months	[1]	(4,964)	(36,948)
AFS Fair Value, 12 months or longer		214,441	275,174
AFS Unrealized Losses, 12 months or longer	[1]	(2,783)	(8,119)
AFS Fair Value		631,075	2,417,607
AFS Unrealized Losses	[1]	(7,747)	(45,067)
AFS Fixed Income Securities [Member] | U.S. Government and Government Agencies [Member]
AFS Fair Value, Less than 12 Months		5,014	6,693
AFS Unrealized Losses, Less than 12 months	[1]	(11)	(174)
AFS Fair Value, 12 months or longer		498	23,163
AFS Unrealized Losses, 12 months or longer	[1]	(1)	(418)
AFS Fair Value		5,512	29,856
AFS Unrealized Losses	[1]	(12)	(592)
AFS Fixed Income Securities [Member] | Foreign Government [Member]
AFS Fair Value, Less than 12 Months			12,208
AFS Unrealized Losses, Less than 12 months	[1]		(93)
AFS Fair Value, 12 months or longer			1,482
AFS Unrealized Losses, 12 months or longer	[1]		(14)
AFS Fair Value			13,690
AFS Unrealized Losses	[1]		(107)
AFS Fixed Income Securities [Member] | Obligations of States and Political Subdivisions [Member]
AFS Fair Value, Less than 12 Months		437	196,798
AFS Unrealized Losses, Less than 12 months	[1]	(4)	(2,074)
AFS Fair Value, 12 months or longer		0	42,821
AFS Unrealized Losses, 12 months or longer	[1]	0	(557)
AFS Fair Value		437	239,619
AFS Unrealized Losses	[1]	(4)	(2,631)
AFS Fixed Income Securities [Member] | Corporate Securities [Member]
AFS Fair Value, Less than 12 Months		89,919	1,041,952
AFS Unrealized Losses, Less than 12 months	[1]	(1,862)	(23,649)
AFS Fair Value, 12 months or longer		15,867	78,953
AFS Unrealized Losses, 12 months or longer	[1]	(537)	(4,316)
AFS Fair Value		105,786	1,120,905
AFS Unrealized Losses	[1]	(2,399)	(27,965)
AFS Fixed Income Securities [Member] | Collateralized Loan Obligations and Other Asset Backed Securities [Member]
AFS Fair Value, Less than 12 Months		176,999	516,106
AFS Unrealized Losses, Less than 12 months	[1]	(2,458)	(6,750)
AFS Fair Value, 12 months or longer		180,898	16,800
AFS Unrealized Losses, 12 months or longer	[1]	(2,195)	(193)
AFS Fair Value		357,897	532,906
AFS Unrealized Losses	[1]	(4,653)	(6,943)
AFS Fixed Income Securities [Member] | Commercial Mortgage Backed Securities [Member]
AFS Fair Value, Less than 12 Months		59,857	229,338
AFS Unrealized Losses, Less than 12 months	[1]	(126)	(2,548)
AFS Fair Value, 12 months or longer		7,665	66,294
AFS Unrealized Losses, 12 months or longer	[1]	(19)	(1,200)
AFS Fair Value		67,522	295,632
AFS Unrealized Losses	[1]	(145)	(3,748)
AFS Fixed Income Securities [Member] | Residential Mortgage Backed Securities [Member]
AFS Fair Value, Less than 12 Months		84,408	139,338
AFS Unrealized Losses, Less than 12 months	[1]	(503)	(1,660)
AFS Fair Value, 12 months or longer		9,513	45,661
AFS Unrealized Losses, 12 months or longer	[1]	(31)	(1,421)
AFS Fair Value		93,921	184,999
AFS Unrealized Losses	[1]	(534)	$ (3,081)
Available-for-sale Securities [Member] | AFS Fixed Income Securities [Member]
AFS Unrealized Losses 9/30/2019 compared to 12/31/2018	[1]	$ (37,300)
[1] Gross unrealized losses include non-OTTI unrealized amounts and OTTI losses recognized in AOCI.

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