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Investments (Fair Value and Gross Pre-Tax Net Unrealized Unrecognized Loss of Securities By Length of Time) (Details) - USD ($) $ in Thousands		Mar. 31, 2017	Dec. 31, 2016
AFS Fair Value, Less than 12 months		$ 795,463	$ 1,358,111
AFS Unrealized Losses, Less than 12 months	[1]	(8,149)	(15,651)
AFS Fair Value, 12 months or longer		2,800	15,626
AFS Unrealized Losses, 12 months or longer	[1]	(85)	(406)
Available-for-sale Securities, Continuous Unrealized Loss Position, Fair Value		798,263	1,373,737
Available-for-sale Securities, Continuous Unrealized Loss Position, Accumulated Loss	[1]	(8,234)	(16,057)
AFS Fixed Income Securities [Member]
AFS Fair Value, Less than 12 months		783,848	1,340,672
AFS Unrealized Losses, Less than 12 months	[1]	(7,823)	(14,991)
AFS Fair Value, 12 months or longer		2,800	15,626
AFS Unrealized Losses, 12 months or longer	[1]	(85)	(406)
Available-for-sale Securities, Continuous Unrealized Loss Position, Fair Value		786,648	1,356,298
Available-for-sale Securities, Continuous Unrealized Loss Position, Accumulated Loss	[1]	(7,908)	(15,397)
AFS Fixed Income Securities [Member] | U.S. Government and Government Agencies [Member]
AFS Fair Value, Less than 12 months		9,012	6,419
AFS Unrealized Losses, Less than 12 months	[1]	(44)	(36)
AFS Fair Value, 12 months or longer		0	0
AFS Unrealized Losses, 12 months or longer	[1]	0	0
Available-for-sale Securities, Continuous Unrealized Loss Position, Fair Value		9,012	6,419
Available-for-sale Securities, Continuous Unrealized Loss Position, Accumulated Loss	[1]	(44)	(36)
AFS Fixed Income Securities [Member] | Foreign Government [Member]
AFS Fair Value, Less than 12 months			13,075
AFS Unrealized Losses, Less than 12 months	[1]		(16)
AFS Fair Value, 12 months or longer			0
AFS Unrealized Losses, 12 months or longer	[1]		0
Available-for-sale Securities, Continuous Unrealized Loss Position, Fair Value			13,075
Available-for-sale Securities, Continuous Unrealized Loss Position, Accumulated Loss	[1]		(16)
AFS Fixed Income Securities [Member] | Obligations of States and Political Subdivisions [Member]
AFS Fair Value, Less than 12 months		114,632	306,509
AFS Unrealized Losses, Less than 12 months	[1]	(2,948)	(5,304)
AFS Fair Value, 12 months or longer		0	0
AFS Unrealized Losses, 12 months or longer	[1]	0	0
Available-for-sale Securities, Continuous Unrealized Loss Position, Fair Value		114,632	306,509
Available-for-sale Securities, Continuous Unrealized Loss Position, Accumulated Loss	[1]	(2,948)	(5,304)
AFS Fixed Income Securities [Member] | Corporate Securities [Member]
AFS Fair Value, Less than 12 months		229,836	462,902
AFS Unrealized Losses, Less than 12 months	[1]	(2,068)	(5,771)
AFS Fair Value, 12 months or longer		244	4,913
AFS Unrealized Losses, 12 months or longer	[1]	(5)	(89)
Available-for-sale Securities, Continuous Unrealized Loss Position, Fair Value		230,080	467,815
Available-for-sale Securities, Continuous Unrealized Loss Position, Accumulated Loss	[1]	(2,073)	(5,860)
AFS Fixed Income Securities [Member] | Collateralized Loan Obligations and Other Asset Backed Securities [Member]
AFS Fair Value, Less than 12 months		137,388	189,795
AFS Unrealized Losses, Less than 12 months	[1]	(400)	(354)
AFS Fair Value, 12 months or longer		310	319
AFS Unrealized Losses, 12 months or longer	[1]	(1)	(1)
Available-for-sale Securities, Continuous Unrealized Loss Position, Fair Value		137,698	190,114
Available-for-sale Securities, Continuous Unrealized Loss Position, Accumulated Loss	[1]	(401)	(355)
AFS Fixed Income Securities [Member] | Commercial Mortgage Backed Securities [Member]
AFS Fair Value, Less than 12 months		80,494	82,492
AFS Unrealized Losses, Less than 12 months	[1]	(775)	(1,021)
AFS Fair Value, 12 months or longer		0	1,645
AFS Unrealized Losses, 12 months or longer	[1]	0	(7)
Available-for-sale Securities, Continuous Unrealized Loss Position, Fair Value		80,494	84,137
Available-for-sale Securities, Continuous Unrealized Loss Position, Accumulated Loss	[1]	(775)	(1,028)
AFS Fixed Income Securities [Member] | Residential Mortgage Backed Securities [Member]
AFS Fair Value, Less than 12 months		212,486	279,480
AFS Unrealized Losses, Less than 12 months	[1]	(1,588)	(2,489)
AFS Fair Value, 12 months or longer		2,246	8,749
AFS Unrealized Losses, 12 months or longer	[1]	(79)	(309)
Available-for-sale Securities, Continuous Unrealized Loss Position, Fair Value		214,732	288,229
Available-for-sale Securities, Continuous Unrealized Loss Position, Accumulated Loss	[1]	(1,667)	(2,798)
Equity Securities [Member]
AFS Fair Value, Less than 12 months		11,615	17,439
AFS Unrealized Losses, Less than 12 months	[1]	(326)	(660)
AFS Fair Value, 12 months or longer		0	0
AFS Unrealized Losses, 12 months or longer	[1]	0	0
Available-for-sale Securities, Continuous Unrealized Loss Position, Fair Value		11,615	17,439
Available-for-sale Securities, Continuous Unrealized Loss Position, Accumulated Loss	[1]	(326)	(660)
Equity Securities [Member] | Common Stock [Member]
AFS Fair Value, Less than 12 months		10,088	11,271
AFS Unrealized Losses, Less than 12 months	[1]	(285)	(305)
AFS Fair Value, 12 months or longer		0	0
AFS Unrealized Losses, 12 months or longer	[1]	0	0
Available-for-sale Securities, Continuous Unrealized Loss Position, Fair Value		10,088	11,271
Available-for-sale Securities, Continuous Unrealized Loss Position, Accumulated Loss	[1]	(285)	(305)
Equity Securities [Member] | Preferred Stock [Member]
AFS Fair Value, Less than 12 months		1,527	6,168
AFS Unrealized Losses, Less than 12 months	[1]	(41)	(355)
AFS Fair Value, 12 months or longer		0	0
AFS Unrealized Losses, 12 months or longer	[1]	0	0
Available-for-sale Securities, Continuous Unrealized Loss Position, Fair Value		1,527	6,168
Available-for-sale Securities, Continuous Unrealized Loss Position, Accumulated Loss	[1]	$ (41)	$ (355)
[1] Gross unrealized losses include non-OTTI unrealized amounts and OTTI losses recognized in AOCI.

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- Definition

Amount of accumulated unrealized loss on investments in debt and equity securities classified as available-for-sale that have been in a continuous loss position for twelve months or longer.

+ References

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-Publisher FASB
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