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Investments (Available-For-Sale Securities Disclosure) (Details) - USD ($) $ in Thousands | Sep. 30, 2015 | Dec. 31, 2014
--- | --- | ---
Schedule of Available-for-sale Securities [Line Items] |  |  |
Cost/Amortized Cost |  | $ 4,494,591 | $ 4,134,797
Unrealized Gains |  | 102,250 | 133,303
Unrealized Losses |  | (23,844) | (10,578)
Total AFS securities |  | 4,572,997 | 4,257,522
AFS Fixed Income Securities [Member] |  |  |
Schedule of Available-for-sale Securities [Line Items] |  |  |
Cost/Amortized Cost |  | 4,273,771 | 3,975,786
Unrealized Gains |  | 88,662 | 100,578
Unrealized Losses |  | (11,387) | (10,242)
Total AFS securities |  | 4,351,046 | 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 |  | 109,062 | 116,666
Unrealized Gains |  | 6,069 | 7,592
Unrealized Losses |  | (1) | (128)
Total AFS securities |  | 115,130 | 124,130
AFS Fixed Income Securities [Member] | Foreign Government [Member] |  |  |
Schedule of Available-for-sale Securities [Line Items] |  |  |
Cost/Amortized Cost |  | 19,030 | 27,035
Unrealized Gains |  | 657 | 796
Unrealized Losses |  | 0 | 0
Total AFS securities |  | 19,687 | 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 |  | 1,303,188 | 1,208,776
Unrealized Gains |  | 35,552 | 38,217
Unrealized Losses |  | (545) | (729)
Total AFS securities |  | 1,338,195 | 1,246,264
AFS Fixed Income Securities [Member] | Corporate Securities [Member] |  |  |
Schedule of Available-for-sale Securities [Line Items] |  |  |
Cost/Amortized Cost |  | 1,859,834 | 1,763,427
Unrealized Gains |  | 35,222 | 42,188
Unrealized Losses |  | (8,882) | (5,809)
Total AFS securities |  | 1,886,174 | 1,799,806
AFS Fixed Income Securities [Member] | Asset-Backed Securities [Member] |  |  |
Schedule of Available-for-sale Securities [Line Items] |  |  |
Cost/Amortized Cost |  | 255,716 | 176,837
Unrealized Gains |  | 1,312 | 760
Unrealized Losses |  | (105) | (373)
Total AFS securities |  | 256,923 | 177,224
AFS Fixed Income Securities [Member] | Commercial Mortgage Backed Securities [Member] |  |  |
Schedule of Available-for-sale Securities [Line Items] |  |  |
Cost/Amortized Cost | [1] | 220,009 | 177,932
Unrealized Gains | [1] | 2,450 | 2,438
Unrealized Losses | [1] | (457) | (777)
Total AFS securities | [1] | 222,002 | 179,593
Government guaranteed agency securities fair value |  | 7,400 | 13,200
AFS Fixed Income Securities [Member] | Residential Mortgage Backed Securities [Member] |  |  |
Schedule of Available-for-sale Securities [Line Items] |  |  |
Cost/Amortized Cost | [2] | 506,932 | 505,113
Unrealized Gains | [2] | 7,400 | 8,587
Unrealized Losses | [2] | (1,397) | (2,426)
Total AFS securities | [2] | 512,935 | 511,274
Government guaranteed agency securities fair value |  | 22,500 | 32,400
Equity Securities [Member] |  |  |
Schedule of Available-for-sale Securities [Line Items] |  |  |
Cost/Amortized Cost |  | 220,820 | 159,011
Unrealized Gains |  | 13,588 | 32,725
Unrealized Losses |  | (12,457) | (336)
Total AFS securities |  | 221,951 | 191,400
Equity Securities [Member] | Common Stock [Member] |  |  |
Schedule of Available-for-sale Securities [Line Items] |  |  |
Cost/Amortized Cost |  | 208,995 | 159,011
Unrealized Gains |  | 13,542 | 32,725
Unrealized Losses |  | (12,340) | (336)
Total AFS securities |  | 210,197 | $ 191,400
Equity Securities [Member] | Preferred Stock [Member] |  |  |
Schedule of Available-for-sale Securities [Line Items] |  |  |
Cost/Amortized Cost |  | 11,825 |
Unrealized Gains |  | 46 |
Unrealized Losses |  | (117) |
Total AFS securities |  | $ 11,754 |
[1] | CMBS includes government guaranteed agency securities with a fair value of $7.4 million at September 30, 2015 and $13.2 million at December 31, 2014.
[2] | RMBS includes government guaranteed agency securities with a fair value of $22.5 million at September 30, 2015 and $32.4 million at December 31, 2014.

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