Investments (Available-For-Sale Securities Disclosure) (Details) - USD ($) $ in Thousands	Jun. 30, 2016	Dec. 31, 2015
Schedule of Available-for-sale Securities [Line Items]
Cost/Amortized Cost	$ 4,633,461	$ 4,546,330
Unrealized Gains	194,745	93,777
Unrealized Losses	(3,482)	(24,853)
Total AFS securities	4,824,724	4,615,254
AFS Fixed Income Securities [Member]
Schedule of Available-for-sale Securities [Line Items]
Cost/Amortized Cost	4,506,580	4,352,514
Unrealized Gains	167,665	78,504
Unrealized Losses	(2,459)	(22,815)
Total AFS securities	4,671,786	4,408,203
AFS Fixed Income Securities [Member] \| U.S. Government and Government Agencies [Member]
Schedule of Available-for-sale Securities [Line Items]
Cost/Amortized Cost	91,933	99,485
Unrealized Gains	4,237	4,721
Unrealized Losses	0	(91)
Total AFS securities	96,170	104,115
AFS Fixed Income Securities [Member] \| Foreign Government [Member]
Schedule of Available-for-sale Securities [Line Items]
Cost/Amortized Cost	8,635	14,885
Unrealized Gains	424	298
Unrealized Losses	0	(2)
Total AFS securities	9,059	15,181
AFS Fixed Income Securities [Member] \| Obligations of States and Political Subdivisions [Member]
Schedule of Available-for-sale Securities [Line Items]
Cost/Amortized Cost	1,379,548	1,314,779
Unrealized Gains	82,604	44,523
Unrealized Losses	0	(160)
Total AFS securities	1,462,152	1,359,142
AFS Fixed Income Securities [Member] \| Corporate Securities [Member]
Schedule of Available-for-sale Securities [Line Items]
Cost/Amortized Cost	1,977,838	1,892,296
Unrealized Gains	62,233	23,407
Unrealized Losses	(1,963)	(15,521)
Total AFS securities	2,038,108	1,900,182
AFS Fixed Income Securities [Member] \| Asset-Backed Securities [Member]
Schedule of Available-for-sale Securities [Line Items]
Cost/Amortized Cost	257,182	244,541
Unrealized Gains	1,656	531
Unrealized Losses	(127)	(918)
Total AFS securities	258,711	244,154
AFS Fixed Income Securities [Member] \| Commercial Mortgage Backed Securities [Member]
Schedule of Available-for-sale Securities [Line Items]
Cost/Amortized Cost	249,603	245,252
Unrealized Gains	6,484	750
Unrealized Losses	(51)	(2,410)
Total AFS securities	256,036	243,592
AFS Fixed Income Securities [Member] \| Residential Mortgage Backed Securities [Member]
Schedule of Available-for-sale Securities [Line Items]
Cost/Amortized Cost	541,841	541,276
Unrealized Gains	10,027	4,274
Unrealized Losses	(318)	(3,713)
Total AFS securities	551,550	541,837
Equity Securities [Member]
Schedule of Available-for-sale Securities [Line Items]
Cost/Amortized Cost	126,881	193,816
Unrealized Gains	27,080	15,273
Unrealized Losses	(1,023)	(2,038)
Total AFS securities	152,938	207,051
Equity Securities [Member] \| Common Stock [Member]
Schedule of Available-for-sale Securities [Line Items]
Cost/Amortized Cost	114,099	181,991
Unrealized Gains	26,343	14,796
Unrealized Losses	(1,023)	(1,998)
Total AFS securities	139,419	194,789
Equity Securities [Member] \| Preferred Stock [Member]
Schedule of Available-for-sale Securities [Line Items]
Cost/Amortized Cost	12,782	11,825
Unrealized Gains	737	477
Unrealized Losses	0	(40)
Total AFS securities	$ 13,519	$ 12,262

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

Reference 1: http://www.xbrl.org/2003/role/presentationRef
-Publisher FASB
-Name Accounting Standards Codification
-Topic 320
-SubTopic 10
-Section 25
-Paragraph 1
-Subparagraph (b)
-URI http://asc.fasb.org/extlink&oid=65884222&loc=d3e22054-111558

Reference 2: http://www.xbrl.org/2003/role/presentationRef
-Publisher FASB
-Name Accounting Standards Codification
-Topic 320
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-Section 50
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Reference 3: http://www.xbrl.org/2003/role/presentationRef
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Reference 1: http://www.xbrl.org/2003/role/presentationRef
-Publisher FASB
-Name Accounting Standards Codification
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