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Fair Value Measurements - Fair Value Hierarchy (Details) (USD $)
In Thousands, unless otherwise specified |
6 Months Ended | |||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||
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Jun. 30, 2013
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Dec. 31, 2012
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Jun. 30, 2013
Other investments [Member]
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Jun. 30, 2013
Fair Value, Measurements, Recurring [Member]
Quoted Prices in Active Markets for Identical Assets (Level 1) [Member]
|
Dec. 31, 2012
Fair Value, Measurements, Recurring [Member]
Quoted Prices in Active Markets for Identical Assets (Level 1) [Member]
|
Jun. 30, 2013
Fair Value, Measurements, Recurring [Member]
Quoted Prices in Active Markets for Identical Assets (Level 1) [Member]
U.S. treasury bonds [Member]
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Dec. 31, 2012
Fair Value, Measurements, Recurring [Member]
Quoted Prices in Active Markets for Identical Assets (Level 1) [Member]
U.S. treasury bonds [Member]
|
Jun. 30, 2013
Fair Value, Measurements, Recurring [Member]
Quoted Prices in Active Markets for Identical Assets (Level 1) [Member]
U.S. agency bonds – mortgage-backed [Member]
|
Dec. 31, 2012
Fair Value, Measurements, Recurring [Member]
Quoted Prices in Active Markets for Identical Assets (Level 1) [Member]
U.S. agency bonds – mortgage-backed [Member]
|
Jun. 30, 2013
Fair Value, Measurements, Recurring [Member]
Quoted Prices in Active Markets for Identical Assets (Level 1) [Member]
U.S. agency bonds – other [Member]
|
Dec. 31, 2012
Fair Value, Measurements, Recurring [Member]
Quoted Prices in Active Markets for Identical Assets (Level 1) [Member]
U.S. agency bonds – other [Member]
|
Jun. 30, 2013
Fair Value, Measurements, Recurring [Member]
Quoted Prices in Active Markets for Identical Assets (Level 1) [Member]
Non-U.S. government bonds [Member]
|
Dec. 31, 2012
Fair Value, Measurements, Recurring [Member]
Quoted Prices in Active Markets for Identical Assets (Level 1) [Member]
Non-U.S. government bonds [Member]
|
Jun. 30, 2013
Fair Value, Measurements, Recurring [Member]
Quoted Prices in Active Markets for Identical Assets (Level 1) [Member]
Other mortgage-backed securities [Member]
|
Dec. 31, 2012
Fair Value, Measurements, Recurring [Member]
Quoted Prices in Active Markets for Identical Assets (Level 1) [Member]
Other mortgage-backed securities [Member]
|
Jun. 30, 2013
Fair Value, Measurements, Recurring [Member]
Quoted Prices in Active Markets for Identical Assets (Level 1) [Member]
Corporate bonds [Member]
|
Dec. 31, 2012
Fair Value, Measurements, Recurring [Member]
Quoted Prices in Active Markets for Identical Assets (Level 1) [Member]
Corporate bonds [Member]
|
Jun. 30, 2013
Fair Value, Measurements, Recurring [Member]
Quoted Prices in Active Markets for Identical Assets (Level 1) [Member]
Municipal bonds [Member]
|
Dec. 31, 2012
Fair Value, Measurements, Recurring [Member]
Quoted Prices in Active Markets for Identical Assets (Level 1) [Member]
Municipal bonds [Member]
|
Jun. 30, 2013
Fair Value, Measurements, Recurring [Member]
Significant Other Observable Inputs (Level 2) [Member]
|
Dec. 31, 2012
Fair Value, Measurements, Recurring [Member]
Significant Other Observable Inputs (Level 2) [Member]
|
Jun. 30, 2013
Fair Value, Measurements, Recurring [Member]
Significant Other Observable Inputs (Level 2) [Member]
U.S. treasury bonds [Member]
|
Dec. 31, 2012
Fair Value, Measurements, Recurring [Member]
Significant Other Observable Inputs (Level 2) [Member]
U.S. treasury bonds [Member]
|
Jun. 30, 2013
Fair Value, Measurements, Recurring [Member]
Significant Other Observable Inputs (Level 2) [Member]
U.S. agency bonds – mortgage-backed [Member]
|
Dec. 31, 2012
Fair Value, Measurements, Recurring [Member]
Significant Other Observable Inputs (Level 2) [Member]
U.S. agency bonds – mortgage-backed [Member]
|
Jun. 30, 2013
Fair Value, Measurements, Recurring [Member]
Significant Other Observable Inputs (Level 2) [Member]
U.S. agency bonds – other [Member]
|
Dec. 31, 2012
Fair Value, Measurements, Recurring [Member]
Significant Other Observable Inputs (Level 2) [Member]
U.S. agency bonds – other [Member]
|
Jun. 30, 2013
Fair Value, Measurements, Recurring [Member]
Significant Other Observable Inputs (Level 2) [Member]
Non-U.S. government bonds [Member]
|
Dec. 31, 2012
Fair Value, Measurements, Recurring [Member]
Significant Other Observable Inputs (Level 2) [Member]
Non-U.S. government bonds [Member]
|
Jun. 30, 2013
Fair Value, Measurements, Recurring [Member]
Significant Other Observable Inputs (Level 2) [Member]
Other mortgage-backed securities [Member]
|
Dec. 31, 2012
Fair Value, Measurements, Recurring [Member]
Significant Other Observable Inputs (Level 2) [Member]
Other mortgage-backed securities [Member]
|
Jun. 30, 2013
Fair Value, Measurements, Recurring [Member]
Significant Other Observable Inputs (Level 2) [Member]
Corporate bonds [Member]
|
Dec. 31, 2012
Fair Value, Measurements, Recurring [Member]
Significant Other Observable Inputs (Level 2) [Member]
Corporate bonds [Member]
|
Jun. 30, 2013
Fair Value, Measurements, Recurring [Member]
Significant Other Observable Inputs (Level 2) [Member]
Municipal bonds [Member]
|
Dec. 31, 2012
Fair Value, Measurements, Recurring [Member]
Significant Other Observable Inputs (Level 2) [Member]
Municipal bonds [Member]
|
Jun. 30, 2013
Fair Value, Measurements, Recurring [Member]
Significant Unobservable Inputs (Level 3) [Member]
|
Dec. 31, 2012
Fair Value, Measurements, Recurring [Member]
Significant Unobservable Inputs (Level 3) [Member]
|
Jun. 30, 2013
Fair Value, Measurements, Recurring [Member]
Significant Unobservable Inputs (Level 3) [Member]
U.S. treasury bonds [Member]
|
Dec. 31, 2012
Fair Value, Measurements, Recurring [Member]
Significant Unobservable Inputs (Level 3) [Member]
U.S. treasury bonds [Member]
|
Jun. 30, 2013
Fair Value, Measurements, Recurring [Member]
Significant Unobservable Inputs (Level 3) [Member]
U.S. agency bonds – mortgage-backed [Member]
|
Dec. 31, 2012
Fair Value, Measurements, Recurring [Member]
Significant Unobservable Inputs (Level 3) [Member]
U.S. agency bonds – mortgage-backed [Member]
|
Jun. 30, 2013
Fair Value, Measurements, Recurring [Member]
Significant Unobservable Inputs (Level 3) [Member]
U.S. agency bonds – other [Member]
|
Dec. 31, 2012
Fair Value, Measurements, Recurring [Member]
Significant Unobservable Inputs (Level 3) [Member]
U.S. agency bonds – other [Member]
|
Jun. 30, 2013
Fair Value, Measurements, Recurring [Member]
Significant Unobservable Inputs (Level 3) [Member]
Non-U.S. government bonds [Member]
|
Dec. 31, 2012
Fair Value, Measurements, Recurring [Member]
Significant Unobservable Inputs (Level 3) [Member]
Non-U.S. government bonds [Member]
|
Jun. 30, 2013
Fair Value, Measurements, Recurring [Member]
Significant Unobservable Inputs (Level 3) [Member]
Other mortgage-backed securities [Member]
|
Dec. 31, 2012
Fair Value, Measurements, Recurring [Member]
Significant Unobservable Inputs (Level 3) [Member]
Other mortgage-backed securities [Member]
|
Jun. 30, 2013
Fair Value, Measurements, Recurring [Member]
Significant Unobservable Inputs (Level 3) [Member]
Corporate bonds [Member]
|
Dec. 31, 2012
Fair Value, Measurements, Recurring [Member]
Significant Unobservable Inputs (Level 3) [Member]
Corporate bonds [Member]
|
Jun. 30, 2013
Fair Value, Measurements, Recurring [Member]
Significant Unobservable Inputs (Level 3) [Member]
Municipal bonds [Member]
|
Dec. 31, 2012
Fair Value, Measurements, Recurring [Member]
Significant Unobservable Inputs (Level 3) [Member]
Municipal bonds [Member]
|
Jun. 30, 2013
Fair Value, Measurements, Recurring [Member]
Total Fair Value [Member]
|
Dec. 31, 2012
Fair Value, Measurements, Recurring [Member]
Total Fair Value [Member]
|
Jun. 30, 2013
Fair Value, Measurements, Recurring [Member]
Total Fair Value [Member]
Fixed Maturities [Member]
|
Jun. 30, 2013
Fair Value, Measurements, Recurring [Member]
Total Fair Value [Member]
U.S. treasury bonds [Member]
|
Dec. 31, 2012
Fair Value, Measurements, Recurring [Member]
Total Fair Value [Member]
U.S. treasury bonds [Member]
|
Jun. 30, 2013
Fair Value, Measurements, Recurring [Member]
Total Fair Value [Member]
U.S. agency bonds – mortgage-backed [Member]
|
Dec. 31, 2012
Fair Value, Measurements, Recurring [Member]
Total Fair Value [Member]
U.S. agency bonds – mortgage-backed [Member]
|
Jun. 30, 2013
Fair Value, Measurements, Recurring [Member]
Total Fair Value [Member]
U.S. agency bonds – other [Member]
|
Dec. 31, 2012
Fair Value, Measurements, Recurring [Member]
Total Fair Value [Member]
U.S. agency bonds – other [Member]
|
Jun. 30, 2013
Fair Value, Measurements, Recurring [Member]
Total Fair Value [Member]
Non-U.S. government bonds [Member]
|
Dec. 31, 2012
Fair Value, Measurements, Recurring [Member]
Total Fair Value [Member]
Non-U.S. government bonds [Member]
|
Jun. 30, 2013
Fair Value, Measurements, Recurring [Member]
Total Fair Value [Member]
Other mortgage-backed securities [Member]
|
Dec. 31, 2012
Fair Value, Measurements, Recurring [Member]
Total Fair Value [Member]
Other mortgage-backed securities [Member]
|
Jun. 30, 2013
Fair Value, Measurements, Recurring [Member]
Total Fair Value [Member]
Corporate bonds [Member]
|
Dec. 31, 2012
Fair Value, Measurements, Recurring [Member]
Total Fair Value [Member]
Corporate bonds [Member]
|
Jun. 30, 2013
Fair Value, Measurements, Recurring [Member]
Total Fair Value [Member]
Municipal bonds [Member]
|
Dec. 31, 2012
Fair Value, Measurements, Recurring [Member]
Total Fair Value [Member]
Municipal bonds [Member]
|
|
| Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items] | ||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||
| Fixed maturities, fair value | $ 17,446 | $ 43,931 | $ 0 | $ 0 | $ 0 | $ 0 | $ 0 | $ 0 | $ 0 | $ 0 | $ 0 | $ 0 | $ 0 | $ 0 | $ 0 | $ 0 | $ 1,218,486 | $ 992,174 | $ 12,856 | $ 13,089 | $ 58,481 | $ 57,433 | $ 27,463 | $ 24,068 | $ 1,366,640 | $ 1,354,154 | $ 13,495 | $ 133,848 | $ 0 | $ 0 | $ 0 | $ 0 | $ 0 | $ 0 | $ 0 | $ 0 | $ 0 | $ 0 | $ 0 | $ 0 | $ 0 | $ 0 | $ 17,446 | $ 43,931 | $ 1,218,486 | $ 992,174 | $ 12,856 | $ 13,089 | $ 58,481 | $ 57,433 | $ 27,463 | $ 24,068 | $ 1,366,640 | $ 1,354,154 | $ 13,495 | $ 133,848 | ||||||||||||
| Other investments, fair value | 0 | 0 | 0 | 0 | 4,438 | 2,901 | 4,438 | 2,901 | ||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||
| Total | 17,446 | 43,931 | 2,697,421 | 2,574,766 | 4,438 | 2,901 | 2,719,305 | 2,621,598 | ||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||
| Percentage of total assets | 0.40% | 1.10% | 61.20% | 62.20% | 0.10% | 0.10% | 61.70% | 63.40% | ||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||
| Percent of fixed maturities valued by a pricing service | 99.80% | |||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||
| Other investments | $ 4,438 | $ 2,901 | $ 4,438 | |||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||
| Other investments, percent of assets | 0.20% | |||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||