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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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