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Fair Value Measurements - Additional Information (Details) (USD $)
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Mar. 31, 2015
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Dec. 31, 2014
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Mar. 31, 2014
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| Schedule of Available-for-sale Securities [Line Items] |
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|
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| Percentage of carrying value of investments from external pricing services |
98.00% |
97.00% |
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| Percentage of carrying value of investments from brokers |
1.00% |
1.00% |
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| Percentage of carrying value of investments from internal matrices and calculations |
1.00% |
2.00% |
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| Assets, transfers from Level 1 to Level 2 |
$ 0 |
|
$ 0 |
| Liabilities, transfers from Level 1 to Level 2 |
0 |
|
0 |
| Assets, transfers from Level 2 to Level 1 |
0 |
|
0 |
| Liabilities, transfers from Level 2 to Level 1 |
0 |
|
0 |
| Fixed maturity securities available for sale, at fair value |
2,765,610,000 |
2,726,731,000 |
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| Maximum liability reduction due to ten percent increase in mortality assumption |
100,000 |
|
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| Liability increase due to ten percent decrease in lapse assumption |
200,000 |
|
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| Liability increase due to ten percent increase in estimated benefit utilization |
700,000 |
|
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| Liability decrease due to ten basis point increase in credit spreads |
300,000 |
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| Level 3 |
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|
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| Schedule of Available-for-sale Securities [Line Items] |
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|
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| Fixed maturity securities available for sale, at fair value |
$ 900,000 |
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