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Investments (Available-For-Sale Securities Disclosure) (Details) (USD $) | Jun. 30, 2013 | Dec. 31, 2012
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Schedule of Available-for-sale Securities [Line Items] |  |  |  |
Cost/Amortized Cost | $ 3,506,428,000 |  | $ 3,263,124,000 |
Unrealized Gains | 131,637,000 |  | 187,105,000 |
Unrealized Losses | (46,190,000) |  | (2,834,000) |
Fair Value | 3,591,875,000 |  | 3,447,395,000 |
AFS Fixed Maturity Securities [Member] |  |  |  |
Schedule of Available-for-sale Securities [Line Items] |  |  |  |
Cost/Amortized Cost | 3,363,994,000 |  | 3,130,683,000 |
Unrealized Gains | 101,242,000 |  | 167,705,000 |
Unrealized Losses | (45,425,000) |  | (2,375,000) |
Fair Value | 3,419,811,000 |  | 3,296,013,000 |
AFS Fixed Maturity Securities [Member] | U.S. Government and Government Agencies [Member] |  |  |  |
Schedule of Available-for-sale Securities [Line Items] |  |  |  |
Cost/Amortized Cost | 165,844,000 |  | 241,874,000 |
Unrealized Gains | 12,519,000 |  | 17,219,000 |
Unrealized Losses | (369,000) |  | (1,000) |
Fair Value | 177,994,000 |  | 259,092,000 |
AFS Fixed Maturity Securities [Member] | Foreign Government [Member] |  |  |  |
Schedule of Available-for-sale Securities [Line Items] |  |  |  |
Cost/Amortized Cost | 28,802,000 |  | 28,813,000 |
Unrealized Gains | 995,000 |  | 1,540,000 |
Unrealized Losses | (127,000) |  | (124,000) |
Fair Value | 29,670,000 |  | 30,229,000 |
AFS Fixed Maturity Securities [Member] | Obligations of States and Political Subdivisions [Member] |  |  |  |
Schedule of Available-for-sale Securities [Line Items] |  |  |  |
Cost/Amortized Cost | 884,615,000 |  | 773,953,000 |
Unrealized Gains | 28,521,000 |  | 44,398,000 |
Unrealized Losses | (18,818,000) |  | (327,000) |
Fair Value | 894,318,000 |  | 818,024,000 |
AFS Fixed Maturity Securities [Member] | Corporate Securities [Member] |  |  |  |
Schedule of Available-for-sale Securities [Line Items] |  |  |  |
Cost/Amortized Cost | 1,491,837,000 |  | 1,368,954,000 |
Unrealized Gains | 46,984,000 |  | 81,696,000 |
Unrealized Losses | (14,850,000) |  | (402,000) |
Fair Value | 1,523,971,000 |  | 1,450,248,000 |
AFS Fixed Maturity Securities [Member] | Asset-backed Securities [Member] |  |  |  |
Schedule of Available-for-sale Securities [Line Items] |  |  |  |
Cost/Amortized Cost | 155,338,000 |  | 126,330,000 |
Unrealized Gains | 999,000 |  | 2,319,000 |
Unrealized Losses | (911,000) |  | (9,000) |
Fair Value | 155,426,000 |  | 128,640,000 |
AFS Fixed Maturity Securities [Member] | Commercial Mortgage-backed Securities ("CMBS") [Member] |  |  |  |
Schedule of Available-for-sale Securities [Line Items] |  |  |  |
Cost/Amortized Cost | 137,048,000 | [1] | 133,763,000 | [1]
Unrealized Gains | 2,318,000 | [1] | 4,572,000 | [1]
Unrealized Losses | (3,782,000) | [1] | (1,216,000) | [1]
Fair Value | 135,584,000 | [1] | 137,119,000 | [1]
Government guaranteed agency securities fair value | 39,900,000 |  | 48,900,000 |
AFS Fixed Maturity Securities [Member] | Residential Mortgage Backed Securities ("RMBS") [Member] |  |  |  |
Schedule of Available-for-sale Securities [Line Items] |  |  |  |
Cost/Amortized Cost | 500,510,000 | [2] | 456,996,000 | [2]
Unrealized Gains | 8,906,000 | [2] | 15,961,000 | [2]
Unrealized Losses | (6,568,000) | [2] | (296,000) | [2]
Fair Value | 502,848,000 | [2] | 472,661,000 | [2]
Government guaranteed agency securities fair value | 72,200,000 |  | 91,000,000 |
Equity Securities [Member] |  |  |  |
Schedule of Available-for-sale Securities [Line Items] |  |  |  |
Cost/Amortized Cost | 142,434,000 |  | 132,441,000 |
Unrealized Gains | 30,395,000 |  | 19,400,000 |
Unrealized Losses | (765,000) |  | (459,000) |
Fair Value | $ 172,064,000 |  | $ 151,382,000 |
[1] | CMBS includes government guaranteed agency securities with a fair value of $39.9 million at June 30, 2013 and $48.9 million at December 31, 2012.
[2] | RMBS includes government guaranteed agency securities with a fair value of $72.2 million at June 30, 2013 and $91.0 million at December 31, 2012.

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