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Investments (Available-For-Sale Securities Disclosure) (Details) (USD $) | Sep. 30, 2013 | Dec. 31, 2012
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Schedule of Available-for-sale Securities [Line Items] |  |  |  |
Cost/Amortized Cost | $ 3,732,074,000 |  | $ 3,263,124,000 |
Unrealized gains | 125,389,000 |  | 187,105,000 |
Unrealized Losses | (43,525,000) |  | (2,834,000) |
Fair Value | 3,813,938,000 |  | 3,447,395,000 |
AFS Fixed Maturity Securities [Member] |  |  |  |
Schedule of Available-for-sale Securities [Line Items] |  |  |  |
Cost/Amortized Cost | 3,573,751,000 |  | 3,130,683,000 |
Unrealized gains | 101,328,000 |  | 167,705,000 |
Unrealized Losses | (41,647,000) |  | (2,375,000) |
Fair Value | 3,633,432,000 |  | 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 | 169,163,000 |  | 241,874,000 |
Unrealized gains | 11,953,000 |  | 17,219,000 |
Unrealized Losses | (330,000) |  | (1,000) |
Fair Value | 180,786,000 |  | 259,092,000 |
AFS Fixed Maturity Securities [Member] | Foreign Government [Member] |  |  |  |
Schedule of Available-for-sale Securities [Line Items] |  |  |  |
Cost/Amortized Cost | 28,797,000 |  | 28,813,000 |
Unrealized gains | 996,000 |  | 1,540,000 |
Unrealized Losses | (84,000) |  | (124,000) |
Fair Value | 29,709,000 |  | 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 | 918,403,000 |  | 773,953,000 |
Unrealized gains | 27,705,000 |  | 44,398,000 |
Unrealized Losses | (16,610,000) |  | (327,000) |
Fair Value | 929,498,000 |  | 818,024,000 |
AFS Fixed Maturity Securities [Member] | Corporate Securities [Member] |  |  |  |
Schedule of Available-for-sale Securities [Line Items] |  |  |  |
Cost/Amortized Cost | 1,629,698,000 |  | 1,368,954,000 |
Unrealized gains | 47,932,000 |  | 81,696,000 |
Unrealized Losses | (14,479,000) |  | (402,000) |
Fair Value | 1,663,151,000 |  | 1,450,248,000 |
AFS Fixed Maturity Securities [Member] | Asset-backed Securities [Member] |  |  |  |
Schedule of Available-for-sale Securities [Line Items] |  |  |  |
Cost/Amortized Cost | 150,179,000 |  | 126,330,000 |
Unrealized gains | 1,063,000 |  | 2,319,000 |
Unrealized Losses | (476,000) |  | (9,000) |
Fair Value | 150,766,000 |  | 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 | 152,464,000 | [1] | 133,763,000 | [1]
Unrealized gains | 2,747,000 | [1] | 4,572,000 | [1]
Unrealized Losses | (3,263,000) | [1] | (1,216,000) | [1]
Fair Value | 151,948,000 | [1] | 137,119,000 | [1]
Government guaranteed agency securities fair value | 35,500,000 |  | 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 | 525,047,000 | [2] | 456,996,000 | [2]
Unrealized gains | 8,932,000 | [2] | 15,961,000 | [2]
Unrealized Losses | (6,405,000) | [2] | (296,000) | [2]
Fair Value | 527,574,000 | [2] | 472,661,000 | [2]
Government guaranteed agency securities fair value | 61,400,000 |  | 91,000,000 |
Equity Securities [Member] |  |  |  |
Schedule of Available-for-sale Securities [Line Items] |  |  |  |
Cost/Amortized Cost | 158,323,000 |  | 132,441,000 |
Unrealized gains | 24,061,000 |  | 19,400,000 |
Unrealized Losses | (1,878,000) |  | (459,000) |
Fair Value | $ 180,506,000 |  | $ 151,382,000 |
[1] | CMBS includes government guaranteed agency securities with a fair value of $35.5 million at September 30, 2013 and $48.9 million at December 31, 2012.
[2] | RMBS includes government guaranteed agency securities with a fair value of $61.4 million at September 30, 2013 and $91.0 million at December 31, 2012.

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