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Investments (Fair Value and Gross Pre-Tax Net Unrealized Loss of Securities By Length of Time) (Details) - USD ($) $ in Thousands		Jun. 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		$ 421,272	$ 2,142,433
AFS Unrealized Losses, Less than 12 months	[1]	(4,902)	(36,948)
AFS Fair Value, 12 months or longer		243,180	275,174
AFS Unrealized Losses, 12 months or longer	[1]	(3,978)	(8,119)
AFS Fair Value		664,452	2,417,607
AFS Unrealized Losses	[1]	(8,880)	(45,067)
AFS Fixed Income Securities [Member] | U.S. Government and Government Agencies [Member]
AFS Fair Value, Less than 12 Months		0	6,693
AFS Unrealized Losses, Less than 12 months	[1]	0	(174)
AFS Fair Value, 12 months or longer		5,508	23,163
AFS Unrealized Losses, 12 months or longer	[1]	(20)	(418)
AFS Fair Value		5,508	29,856
AFS Unrealized Losses	[1]	(20)	(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		739	196,798
AFS Unrealized Losses, Less than 12 months	[1]	(6)	(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		739	239,619
AFS Unrealized Losses	[1]	(6)	(2,631)
AFS Fixed Income Securities [Member] | Corporate Securities [Member]
AFS Fair Value, Less than 12 Months		94,964	1,041,952
AFS Unrealized Losses, Less than 12 months	[1]	(2,260)	(23,649)
AFS Fair Value, 12 months or longer		46,527	78,953
AFS Unrealized Losses, 12 months or longer	[1]	(2,142)	(4,316)
AFS Fair Value		141,491	1,120,905
AFS Unrealized Losses	[1]	(4,402)	(27,965)
AFS Fixed Income Securities [Member] | Collateralized Loan Obligations and Other Asset Backed Securities [Member]
AFS Fair Value, Less than 12 Months		231,823	516,106
AFS Unrealized Losses, Less than 12 months	[1]	(2,318)	(6,750)
AFS Fair Value, 12 months or longer		151,572	16,800
AFS Unrealized Losses, 12 months or longer	[1]	(1,623)	(193)
AFS Fair Value		383,395	532,906
AFS Unrealized Losses	[1]	(3,941)	(6,943)
AFS Fixed Income Securities [Member] | Commercial Mortgage Backed Securities [Member]
AFS Fair Value, Less than 12 Months		59,639	229,338
AFS Unrealized Losses, Less than 12 months	[1]	(183)	(2,548)
AFS Fair Value, 12 months or longer		24,882	66,294
AFS Unrealized Losses, 12 months or longer	[1]	(54)	(1,200)
AFS Fair Value		84,521	295,632
AFS Unrealized Losses	[1]	(237)	(3,748)
AFS Fixed Income Securities [Member] | Residential Mortgage Backed Securities [Member]
AFS Fair Value, Less than 12 Months		34,107	139,338
AFS Unrealized Losses, Less than 12 months	[1]	(135)	(1,660)
AFS Fair Value, 12 months or longer		14,691	45,661
AFS Unrealized Losses, 12 months or longer	[1]	(139)	(1,421)
AFS Fair Value		48,798	184,999
AFS Unrealized Losses	[1]	$ (274)	$ (3,081)
[1] Gross unrealized losses include non-OTTI unrealized amounts and OTTI losses recognized in AOCI.

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