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Investments (Available-For-Sale Securities Disclosure) (Details) (USD $) | Jun. 30, 2012 | Dec. 31, 2011
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Schedule of Available-for-sale Securities [Line Items] |  |  |  |
Cost/Amortized Cost | $ 3,105,076,000 |  | $ 2,910,682,000 |
Unrealized Gains | 174,432,000 |  | 153,512,000 |
Unrealized Losses | (8,385,000) |  | (9,466,000) |
Fair Value | 3,271,123,000 |  | 3,054,728,000 |
Corporate securities fully guaranteed by the Federal Deposit Insurance Corporation ("FDIC") | 14,200,000 |  | 76,500,000 |
Commercial Mortgage-backed Securities ("CMBS") [Member] |  |  |  |
Schedule of Available-for-sale Securities [Line Items] |  |  |  |
Government guaranteed agency securities fair value | 67,000,000 |  | 72,900,000 |
Residential Mortgage Backed Securities ("RMBS") [Member] |  |  |  |
Schedule of Available-for-sale Securities [Line Items] |  |  |  |
Government guaranteed agency securities fair value | 102,600,000 |  | 98,200,000 |
AFS Fixed Maturity Securities [Member] |  |  |  |
Schedule of Available-for-sale Securities [Line Items] |  |  |  |
Cost/Amortized Cost | 2,974,819,000 |  | 2,766,856,000 |
Unrealized Gains | 153,785,000 |  | 139,895,000 |
Unrealized Losses | (5,598,000) |  | (9,378,000) |
Fair Value | 3,123,006,000 |  | 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 | 268,949,000 | [1] | 333,504,000 | [1]
Unrealized Gains | 19,050,000 | [1] | 20,292,000 | [1]
Unrealized Losses | (3,000) | [1] | 0 | [1]
Fair Value | 287,996,000 | [1] | 353,796,000 | [1]
AFS Fixed Maturity Securities [Member] | Foreign Government [Member] |  |  |  |
Schedule of Available-for-sale Securities [Line Items] |  |  |  |
Cost/Amortized Cost | 41,557,000 |  | 33,687,000 |
Unrealized Gains | 1,537,000 |  | 1,042,000 |
Unrealized Losses | (312,000) |  | (556,000) |
Fair Value | 42,782,000 |  | 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 | 695,158,000 |  | 578,214,000 |
Unrealized Gains | 42,307,000 |  | 44,491,000 |
Unrealized Losses | (964,000) |  | (46,000) |
Fair Value | 736,501,000 |  | 622,659,000 |
AFS Fixed Maturity Securities [Member] | Corporate Securities [Member] |  |  |  |
Schedule of Available-for-sale Securities [Line Items] |  |  |  |
Cost/Amortized Cost | 1,283,114,000 |  | 1,168,439,000 |
Unrealized Gains | 66,588,000 |  | 50,167,000 |
Unrealized Losses | (955,000) |  | (5,296,000) |
Fair Value | 1,348,747,000 |  | 1,213,310,000 |
AFS Fixed Maturity Securities [Member] | Asset-backed Securities ("ABS") [Member] |  |  |  |
Schedule of Available-for-sale Securities [Line Items] |  |  |  |
Cost/Amortized Cost | 93,031,000 |  | 77,706,000 |
Unrealized Gains | 1,785,000 |  | 1,289,000 |
Unrealized Losses | (7,000) |  | (46,000) |
Fair Value | 94,809,000 |  | 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 | 115,965,000 | [2] | 107,838,000 | [2]
Unrealized Gains | 4,882,000 | [2] | 6,427,000 | [2]
Unrealized Losses | (2,804,000) | [2] | (1,667,000) | [2]
Fair Value | 118,043,000 | [2] | 112,598,000 | [2]
AFS Fixed Maturity Securities [Member] | Residential Mortgage Backed Securities ("RMBS") [Member] |  |  |  |
Schedule of Available-for-sale Securities [Line Items] |  |  |  |
Cost/Amortized Cost | 477,045,000 | [3] | 467,468,000 | [3]
Unrealized Gains | 17,636,000 | [3] | 16,187,000 | [3]
Unrealized Losses | (553,000) | [3] | (1,767,000) | [3]
Fair Value | 494,128,000 | [3] | 481,888,000 | [3]
Equity Securities [Member] |  |  |  |
Schedule of Available-for-sale Securities [Line Items] |  |  |  |
Cost/Amortized Cost | 130,257,000 |  | 143,826,000 |
Unrealized Gains | 20,647,000 |  | 13,617,000 |
Unrealized Losses | (2,787,000) |  | (88,000) |
Fair Value | $ 148,117,000 |  | $ 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 $14.2 million at June 30, 2012 and $76.5 million at December 31, 2011.
[2] | 2 CMBS includes government guaranteed agency securities with a fair value of $67.0 million at June 30, 2012 and $72.9 million at December 31, 2011.
[3] | 3 RMBS includes government guaranteed agency securities with a fair value of $102.6 million at June 30, 2012 and $98.2 million at December 31, 2011.

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