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Fair Value Measurements - Fair Value Hierarchy (Details) (USD $)
In Thousands, unless otherwise specified |
9 Months Ended | |||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||
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Sep. 30, 2013
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Dec. 31, 2012
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Sep. 30, 2013
Other investments [Member]
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Sep. 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]
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Sep. 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]
|
Sep. 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]
|
Sep. 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]
|
Sep. 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]
|
Sep. 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]
|
Sep. 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]
|
Sep. 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]
|
Sep. 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]
|
Sep. 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]
|
Sep. 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]
|
Sep. 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]
|
Sep. 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]
|
Sep. 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]
|
Sep. 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]
|
Sep. 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]
|
Sep. 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]
|
Sep. 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]
|
Sep. 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]
|
Sep. 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]
|
Sep. 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]
|
Sep. 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]
|
Sep. 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]
|
Sep. 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]
|
Sep. 30, 2013
Fair Value, Measurements, Recurring [Member]
Total Fair Value [Member]
|
Dec. 31, 2012
Fair Value, Measurements, Recurring [Member]
Total Fair Value [Member]
|
Sep. 30, 2013
Fair Value, Measurements, Recurring [Member]
Total Fair Value [Member]
Fixed Maturities [Member]
|
Sep. 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]
|
Sep. 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]
|
Sep. 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]
|
Sep. 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]
|
Sep. 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]
|
Sep. 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]
|
Sep. 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 | $ 17,374 | $ 43,931 | $ 0 | $ 0 | $ 0 | $ 0 | $ 0 | $ 0 | $ 0 | $ 0 | $ 0 | $ 0 | $ 0 | $ 0 | $ 0 | $ 0 | $ 1,130,713 | $ 992,174 | $ 8,298 | $ 13,089 | $ 67,282 | $ 57,433 | $ 22,662 | $ 24,068 | $ 1,381,646 | $ 1,354,154 | $ 46,330 | $ 133,848 | $ 0 | $ 0 | $ 0 | $ 0 | $ 0 | $ 0 | $ 0 | $ 0 | $ 0 | $ 0 | $ 0 | $ 0 | $ 0 | $ 0 | $ 17,374 | $ 43,931 | $ 1,130,713 | $ 992,174 | $ 8,298 | $ 13,089 | $ 67,282 | $ 57,433 | $ 22,662 | $ 24,068 | $ 1,381,646 | $ 1,354,154 | $ 46,330 | $ 133,848 | ||||||||||||
| Other investments, fair value | 0 | 0 | 0 | 0 | 5,006 | 2,901 | 5,006 | 2,901 | ||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||
| Total | 17,374 | 43,931 | 2,656,931 | 2,574,766 | 5,006 | 2,901 | 2,679,311 | 2,621,598 | ||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||
| Percentage of total assets | 0.40% | 1.10% | 59.70% | 62.20% | 0.10% | 0.10% | 60.20% | 63.40% | ||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||
| Percent of fixed maturities valued by a pricing service | 99.10% | |||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||
| Other investments | $ 5,006 | $ 2,901 | $ 5,006 | |||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||
| Other investments, percent of assets | 0.20% | |||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||