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Investments (Available-For-Sale Securities Disclosure) (Details) (USD $) | Sep. 30, 2012 | Dec. 31, 2011
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Schedule of Available-for-sale Securities [Line Items] |  |  |  |
Cost/Amortized Cost | $ 3,219,607,000 |  | $ 2,910,682,000 |
Unrealized Gains | 208,389,000 |  | 153,512,000 |
Unrealized Losses | (2,459,000) |  | (9,466,000) |
Fair Value | 3,425,537,000 |  | 3,054,728,000 |
AFS Fixed Maturity Securities [Member] |  |  |  |
Schedule of Available-for-sale Securities [Line Items] |  |  |  |
Cost/Amortized Cost | 3,091,740,000 |  | 2,766,856,000 |
Unrealized Gains | 180,468,000 |  | 139,895,000 |
Unrealized Losses | (2,248,000) |  | (9,378,000) |
Fair Value | 3,269,960,000 |  | 2,897,373,000 |
AFS Fixed Maturity Securities [Member] | U.S. Government and Government Agencies [Member] |  |  |  |
Schedule of Available-for-sale Securities [Line Items] |  |  |  |
Cost/Amortized Cost | 275,417,000 | [1] | 333,504,000 | [1]
Unrealized Gains | 18,797,000 | [1] | 20,292,000 | [1]
Unrealized Losses | 0 | [1] | 0 | [1]
Fair Value | 294,214,000 | [1] | 353,796,000 | [1]
Corporate securities fully guaranteed by the Federal Deposit Insurance Corporation ("FDIC") | 14,100,000 |  | 76,500,000 |
AFS Fixed Maturity Securities [Member] | Foreign Government [Member] |  |  |  |
Schedule of Available-for-sale Securities [Line Items] |  |  |  |
Cost/Amortized Cost | 28,819,000 |  | 33,687,000 |
Unrealized Gains | 1,664,000 |  | 1,042,000 |
Unrealized Losses | (191,000) |  | (556,000) |
Fair Value | 30,292,000 |  | 34,173,000 |
AFS Fixed Maturity Securities [Member] | Obligations of States and Political Subdivisions [Member] |  |  |  |
Schedule of Available-for-sale Securities [Line Items] |  |  |  |
Cost/Amortized Cost | 737,985,000 |  | 578,214,000 |
Unrealized Gains | 46,524,000 |  | 44,491,000 |
Unrealized Losses | (8,000) |  | (46,000) |
Fair Value | 784,501,000 |  | 622,659,000 |
AFS Fixed Maturity Securities [Member] | Corporate Securities [Member] |  |  |  |
Schedule of Available-for-sale Securities [Line Items] |  |  |  |
Cost/Amortized Cost | 1,340,366,000 |  | 1,168,439,000 |
Unrealized Gains | 85,741,000 |  | 50,167,000 |
Unrealized Losses | (219,000) |  | (5,296,000) |
Fair Value | 1,425,888,000 |  | 1,213,310,000 |
AFS Fixed Maturity Securities [Member] | Asset-backed Securities [Member] |  |  |  |
Schedule of Available-for-sale Securities [Line Items] |  |  |  |
Cost/Amortized Cost | 118,923,000 |  | 77,706,000 |
Unrealized Gains | 2,232,000 |  | 1,289,000 |
Unrealized Losses | (1,000) |  | (46,000) |
Fair Value | 121,154,000 |  | 78,949,000 |
AFS Fixed Maturity Securities [Member] | Commercial Mortgage-backed Securities ("CMBS") [Member] |  |  |  |
Schedule of Available-for-sale Securities [Line Items] |  |  |  |
Cost/Amortized Cost | 126,043,000 | [2] | 107,838,000 | [2]
Unrealized Gains | 5,151,000 | [2] | 6,427,000 | [2]
Unrealized Losses | (1,579,000) | [2] | (1,667,000) | [2]
Fair Value | 129,615,000 | [2] | 112,598,000 | [2]
Government guaranteed agency securities fair value | 59,900,000 |  | 72,900,000 |
AFS Fixed Maturity Securities [Member] | Residential Mortgage Backed Securities ("RMBS") [Member] |  |  |  |
Schedule of Available-for-sale Securities [Line Items] |  |  |  |
Cost/Amortized Cost | 464,187,000 | [3] | 467,468,000 | [3]
Unrealized Gains | 20,359,000 | [3] | 16,187,000 | [3]
Unrealized Losses | (250,000) | [3] | (1,767,000) | [3]
Fair Value | 484,296,000 | [3] | 481,888,000 | [3]
Government guaranteed agency securities fair value | 98,100,000 |  | 98,200,000 |
Equity Securities [Member] |  |  |  |
Schedule of Available-for-sale Securities [Line Items] |  |  |  |
Cost/Amortized Cost | 127,867,000 |  | 143,826,000 |
Unrealized Gains | 27,921,000 |  | 13,617,000 |
Unrealized Losses | (211,000) |  | (88,000) |
Fair Value | $ 155,577,000 |  | $ 157,355,000 |
[1] | 1 U.S. government includes corporate securities fully guaranteed by the Federal Deposit Insurance Corporation (“FDIC”) with a fair value of $14.1 million at September 30, 2012 and $76.5 million at December 31, 2011.
[2] | 2 CMBS includes government guaranteed agency securities with a fair value of $59.9 million at September 30, 2012 and $72.9 million at December 31, 2011.
[3] | 3 RMBS includes government guaranteed agency securities with a fair value of $98.1 million at September 30, 2012 and $98.2 million at December 31, 2011.

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