Investments (Available-For-Sale Securities Disclosure) (Details) - USD ($) $ in Thousands	Dec. 31, 2018	Dec. 31, 2017
Debt Securities, Available-for-sale [Line Items]
Cost/Amortized Cost		$ 5,220,527
Unrealized Gains		130,058
Unrealized Losses		(5,358)
Total AFS securities		5,345,227
AFS Fixed Income Securities [Member]
Debt Securities, Available-for-sale [Line Items]
Cost/Amortized Cost	$ 5,270,798	5,076,716
Unrealized Gains	47,369	90,867
Unrealized Losses	(45,067)	(5,061)
Total AFS securities	5,273,100	5,162,522
AFS Fixed Income Securities [Member] \| U.S. Government and Government Agencies [Member]
Debt Securities, Available-for-sale [Line Items]
Cost/Amortized Cost	120,092	49,326
Unrealized Gains	1,810	647
Unrealized Losses	(592)	(233)
Total AFS securities	121,310	49,740
AFS Fixed Income Securities [Member] \| Foreign Government [Member]
Debt Securities, Available-for-sale [Line Items]
Cost/Amortized Cost	23,202	18,040
Unrealized Gains	36	526
Unrealized Losses	(107)	(11)
Total AFS securities	23,131	18,555
AFS Fixed Income Securities [Member] \| Obligations of States and Political Subdivisions [Member]
Debt Securities, Available-for-sale [Line Items]
Cost/Amortized Cost	1,121,615	1,539,307
Unrealized Gains	19,485	44,245
Unrealized Losses	(2,631)	(582)
Total AFS securities	1,138,469	1,582,970
AFS Fixed Income Securities [Member] \| Corporate Securities [Member]
Debt Securities, Available-for-sale [Line Items]
Cost/Amortized Cost	1,639,852	1,588,339
Unrealized Gains	5,521	30,891
Unrealized Losses	(27,965)	(1,762)
Total AFS securities	1,617,408	1,617,468
AFS Fixed Income Securities [Member] \| Collateralized Loan Obligations and Other Asset-Backed Securities [Member]
Debt Securities, Available-for-sale [Line Items]
Cost/Amortized Cost	720,193	789,152
Unrealized Gains	4,112	6,508
Unrealized Losses	(6,943)	(202)
Total AFS securities	717,362	795,458
AFS Fixed Income Securities [Member] \| Commercial Mortgage Backed Securities [Member]
Debt Securities, Available-for-sale [Line Items]
Cost/Amortized Cost	527,409	382,727
Unrealized Gains	3,417	1,563
Unrealized Losses	(3,748)	(841)
Total AFS securities	527,078	383,449
AFS Fixed Income Securities [Member] \| Residential Mortgage Backed Securities [Member]
Debt Securities, Available-for-sale [Line Items]
Cost/Amortized Cost	1,118,435	709,825
Unrealized Gains	12,988	6,487
Unrealized Losses	(3,081)	(1,430)
Total AFS securities	$ 1,128,342	714,882
Equity Securities [Member]
Debt Securities, Available-for-sale [Line Items]
Cost/Amortized Cost		143,811
Unrealized Gains		39,191
Unrealized Losses		(297)
Total AFS securities		182,705
Equity Securities [Member] \| Common Stock [Member]
Debt Securities, Available-for-sale [Line Items]
Cost/Amortized Cost		129,696
Unrealized Gains		38,287
Unrealized Losses		(226)
Total AFS securities		167,757
Equity Securities [Member] \| Nonredeemable Preferred Stock [Member]
Debt Securities, Available-for-sale [Line Items]
Cost/Amortized Cost		14,115
Unrealized Gains		904
Unrealized Losses		(71)
Total AFS securities		$ 14,948

Amount of investment in debt and equity securities categorized neither as held-to-maturity nor trading.

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- Definition

Amount before tax of unrealized gain in accumulated other comprehensive income (AOCI) on investments in debt and equity securities classified as available-for-sale.

+ References

Reference 1: http://fasb.org/us-gaap/role/ref/legacyRef
-Publisher FASB
-Name Accounting Standards Codification
-Topic 320
-SubTopic 10
-Section 50
-Paragraph 2
-Subparagraph (b)
-URI http://asc.fasb.org/extlink&oid=82897076&loc=d3e27161-111563

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Amount before tax of unrealized loss in accumulated other comprehensive income (AOCI) on investments in debt and equity securities classified as available-for-sale.

+ References

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+ References

No definition available.

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