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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, 2020	Dec. 31, 2019
AFS Fixed Income Securities [Member]
AFS Fair Value, Less than 12 Months	$ 686,054	$ 516,259
AFS Unrealized Losses, Less than 12 months	(30,368)	(3,379)
AFS Fair Value, 12 months or longer	159,066	230,770
AFS Unrealized Losses, 12 months or longer	(9,536)	(4,359)
AFS Fair Value	845,120	747,029
AFS Unrealized Losses	(39,904)	(7,738)
AFS Fixed Income Securities [Member] | Foreign Government [Member]
AFS Fair Value, Less than 12 Months	1,673	1,416
AFS Unrealized Losses, Less than 12 months	(104)	(2)
AFS Fair Value, 12 months or longer	0	0
AFS Unrealized Losses, 12 months or longer	0	0
AFS Fair Value	1,673	1,416
AFS Unrealized Losses	(104)	(2)
AFS Fixed Income Securities [Member] | Obligations of States and Political Subdivisions [Member]
AFS Fair Value, Less than 12 Months	9,141	35,838
AFS Unrealized Losses, Less than 12 months	(200)	(270)
AFS Fair Value, 12 months or longer	0	0
AFS Unrealized Losses, 12 months or longer	0	0
AFS Fair Value	9,141	35,838
AFS Unrealized Losses	(200)	(270)
AFS Fixed Income Securities [Member] | Corporate Securities [Member]
AFS Fair Value, Less than 12 Months	175,595	84,832
AFS Unrealized Losses, Less than 12 months	(9,852)	(480)
AFS Fair Value, 12 months or longer	3,216	20,182
AFS Unrealized Losses, 12 months or longer	(450)	(830)
AFS Fair Value	178,811	105,014
AFS Unrealized Losses	(10,302)	(1,310)
AFS Fixed Income Securities [Member] | Collateralized Loan Obligations and Other Asset Backed Securities [Member]
AFS Fair Value, Less than 12 Months	373,896	205,191
AFS Unrealized Losses, Less than 12 months	(16,109)	(1,938)
AFS Fair Value, 12 months or longer	142,759	204,385
AFS Unrealized Losses, 12 months or longer	(8,397)	(3,496)
AFS Fair Value	516,655	409,576
AFS Unrealized Losses	(24,506)	(5,434)
AFS Fixed Income Securities [Member] | Commercial Mortgage Backed Securities [Member]
AFS Fair Value, Less than 12 Months	86,573	62,893
AFS Unrealized Losses, Less than 12 months	(3,128)	(264)
AFS Fair Value, 12 months or longer	11,739	828
AFS Unrealized Losses, 12 months or longer	(656)	(3)
AFS Fair Value	98,312	63,721
AFS Unrealized Losses	(3,784)	(267)
AFS Fixed Income Securities [Member] | Residential Mortgage Backed Securities [Member]
AFS Fair Value, Less than 12 Months	39,176	126,089
AFS Unrealized Losses, Less than 12 months	(975)	(425)
AFS Fair Value, 12 months or longer	1,352	5,375
AFS Unrealized Losses, 12 months or longer	(33)	(30)
AFS Fair Value	40,528	131,464
AFS Unrealized Losses	(1,008)	(455)
Available-for-sale Securities [Member]
AFS Unrealized Losses	$ (39,900)	$ (7,700)

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