v2.4.0.8

Investments - Credit Ratings (Details) (USD $) In Thousands, unless otherwise specified | Jun. 30, 2013 | Dec. 31, 2012
--- | --- | ---
Schedule of Available-for-sale Securities [Line Items] |  |  |  |
Amortized cost | $ 2,665,870 |  | $ 2,475,202 |
Fair value | 2,714,867 |  | 2,618,697 |
% of Total fair value | 100.00% |  | 100.00% |
U.S. treasury bonds [Member] |  |  |  |
Schedule of Available-for-sale Securities [Line Items] |  |  |  |
Amortized cost | 16,635 | [1] | 42,671 | [1]
Fair value | 17,446 | [1] | 43,931 | [1]
% of Total fair value | 0.60% | [1] | 1.70% | [1]
U.S. agency bonds [Member] |  |  |  |
Schedule of Available-for-sale Securities [Line Items] |  |  |  |
Amortized cost | 1,233,289 | [1] | 974,331 | [1]
Fair value | 1,231,342 | [1] | 1,005,263 | [1]
% of Total fair value | 45.40% | [1] | 38.40% | [1]
AAA [Member] |  |  |  |
Schedule of Available-for-sale Securities [Line Items] |  |  |  |
Amortized cost | 161,591 | [1] | 171,136 | [1]
Fair value | 169,409 | [1] | 183,950 | [1]
% of Total fair value | 6.20% | [1] | 7.00% | [1]
AA Plus, AA, AA Minus [Member] |  |  |  |
Schedule of Available-for-sale Securities [Line Items] |  |  |  |
Amortized cost | 72,411 | [1] | 186,495 | [1]
Fair value | 78,688 | [1] | 196,797 | [1]
% of Total fair value | 2.90% | [1] | 7.50% | [1]
A Plus, A, A Minus [Member] |  |  |  |
Schedule of Available-for-sale Securities [Line Items] |  |  |  |
Amortized cost | 477,802 | [1] | 477,236 | [1]
Fair value | 501,369 | [1] | 515,383 | [1]
% of Total fair value | 18.50% | [1] | 19.70% | [1]
BBB Plus, BBB, BBB Minus [Member] |  |  |  |
Schedule of Available-for-sale Securities [Line Items] |  |  |  |
Amortized cost | 665,760 | [1] | 587,858 | [1]
Fair value | 678,419 | [1] | 637,089 | [1]
% of Total fair value | 25.00% | [1] | 24.30% | [1]
BB Plus or Lower [Member] |  |  |  |
Schedule of Available-for-sale Securities [Line Items] |  |  |  |
Amortized cost | 38,382 | [1] | 35,475 | [1]
Fair value | $ 38,194 | [1] | $ 36,284 | [1]
% of Total fair value | 1.40% | [1] | 1.40% | [1]
[1] | Ratings as assigned by Standard & Poor’s ("S&P")

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