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Investments (Available-For-Sale Securities Disclosure) (Details) - USD ($) $ in Thousands	Dec. 31, 2015	Dec. 31, 2014
Schedule of Available-for-sale Securities [Line Items]
Cost/Amortized Cost	$ 4,546,330	$ 4,134,797
Unrealized Gains	93,777	133,299
Unrealized Losses	(24,853)	(10,574)
Total AFS securities	4,615,254	4,257,522
Afs Fixed Maturity Securities [Member] | Commercial Mortgage Backed Securities [Member]
Schedule of Available-for-sale Securities [Line Items]
Government guaranteed agency securities fair value	4,500	13,200
Afs Fixed Maturity Securities [Member] | Residential Mortgage Backed Securities [Member]
Schedule of Available-for-sale Securities [Line Items]
Government guaranteed agency securities fair value	19,700	32,400
AFS Fixed Income Securities [Member]
Schedule of Available-for-sale Securities [Line Items]
Cost/Amortized Cost	4,352,514	3,975,786
Unrealized Gains	78,504	100,578
Unrealized Losses	(22,815)	(10,242)
Total AFS securities	4,408,203	4,066,122
AFS Fixed Income Securities [Member] | U.S. Government and Government Agencies [Member]
Schedule of Available-for-sale Securities [Line Items]
Cost/Amortized Cost	99,485	116,666
Unrealized Gains	4,721	7,592
Unrealized Losses	(91)	(128)
Total AFS securities	104,115	124,130
AFS Fixed Income Securities [Member] | Foreign Government [Member]
Schedule of Available-for-sale Securities [Line Items]
Cost/Amortized Cost	14,885	27,035
Unrealized Gains	298	796
Unrealized Losses	(2)	0
Total AFS securities	15,181	27,831
AFS Fixed Income Securities [Member] | Obligations of States and Political Subdivisions [Member]
Schedule of Available-for-sale Securities [Line Items]
Cost/Amortized Cost	1,314,779	1,208,776
Unrealized Gains	44,523	38,217
Unrealized Losses	(160)	(729)
Total AFS securities	1,359,142	1,246,264
AFS Fixed Income Securities [Member] | Corporate Securities [Member]
Schedule of Available-for-sale Securities [Line Items]
Cost/Amortized Cost	1,892,296	1,763,427
Unrealized Gains	23,407	42,188
Unrealized Losses	(15,521)	(5,809)
Total AFS securities	1,900,182	1,799,806
AFS Fixed Income Securities [Member] | Asset-backed Securities [Member]
Schedule of Available-for-sale Securities [Line Items]
Cost/Amortized Cost	244,541	176,837
Unrealized Gains	531	760
Unrealized Losses	(918)	(373)
Total AFS securities	244,154	177,224
AFS Fixed Income Securities [Member] | Commercial Mortgage Backed Securities [Member]
Schedule of Available-for-sale Securities [Line Items]
Cost/Amortized Cost	245,252	177,932
Unrealized Gains	750	2,438
Unrealized Losses	(2,410)	(777)
Total AFS securities	243,592	179,593
AFS Fixed Income Securities [Member] | Residential Mortgage Backed Securities [Member]
Schedule of Available-for-sale Securities [Line Items]
Cost/Amortized Cost	541,276	505,113
Unrealized Gains	4,274	8,587
Unrealized Losses	(3,713)	(2,426)
Total AFS securities	541,837	511,274
Equity Securities [Member]
Schedule of Available-for-sale Securities [Line Items]
Cost/Amortized Cost	193,816	159,011
Unrealized Gains	15,273	32,721
Unrealized Losses	(2,038)	(332)
Total AFS securities	207,051	191,400
Equity Securities [Member] | Common Stock [Member]
Schedule of Available-for-sale Securities [Line Items]
Cost/Amortized Cost	181,991	159,011
Unrealized Gains	14,796	32,721
Unrealized Losses	(1,998)	(332)
Total AFS securities	194,789	$ 191,400
Equity Securities [Member] | Nonredeemable Preferred Stock [Member]
Schedule of Available-for-sale Securities [Line Items]
Cost/Amortized Cost	11,825
Unrealized Gains	477
Unrealized Losses	(40)
Total AFS securities	$ 12,262

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