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Investments - Additional Information (Detail) (USD $) In Thousands, unless otherwise specified | 12 Months Ended |
--- | --- | ---
Dec. 31, 2012 Security | Dec. 31, 2011
Investments [Line Items] |  |
Unrealized losses of one security under closed-block life insurance issuance | $ 3,548 |
12 Months or Longer, Gross Unrealized Loss | 70,164 | 114,011
Unrealized losses of one security of large diversified financial services company | 3,363 |
Period of unrealized loss position on large diversified financial services company | 66 months |
Unrealized loss position of Alt-A securities greater than twelve months | 15,236 |
Percentage of unrealized losses on mortgage-backed securities attributable to Alt-A Securities | 100.00% |
Number of individual Alt-A securities | 16 |
Unrealized losses on security secured by IRS facility lease payments | 29,838 |
Percentage of permitted policy claim | 25.00% |
Securities fair value | 6,945 | 7,132
Fair value of securities held by bankruptcy remote trust | 201,329 | 172,880
Corporate obligations [Member] |  |
Investments [Line Items] |  |
12 Months or Longer, Gross Unrealized Loss | 8,036 |
Minimum [Member] |  |
Investments [Line Items] |  |
Period of unrealized loss position on closed-block life insurance issuance | 42 months |
Period of unrealized loss position on security secured by IRS facility lease payments | 19 months |
Maximum [Member] |  |
Investments [Line Items] |  |
Period of unrealized loss position on closed-block life insurance issuance | 60 months |
Period of unrealized loss position on security secured by IRS facility lease payments | 60 months |
Below investment grade securities and non rated securities [Member] |  |
Investments [Line Items] |  |
Fair value of below investment grade securities and non-rated securities | 192,190 | 268,633
Gross unrealized loss | 43,934 | 77,947
Residential mortgage-backed securities [Member] |  |
Investments [Line Items] |  |
12 Months or Longer, Gross Unrealized Loss | 15,236 | 43,321
Asset-backed Securities [Member] |  |
Investments [Line Items] |  |
12 Months or Longer, Gross Unrealized Loss | $ 46,503 |

X
- Definition Number of months closed block life insurance issuance in a continuous unrealized loss position. + References No definition available. + Details
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- Definition Number of months an issuance of a large diversified financial services company that is in a continuous unrealized loss position. + References No definition available. + Details
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- Definition Number of months a security that is secured by IRS facility lease payments is in a continuous unrealized loss position. + References No definition available. + Details
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- Definition Aggregate losses for a closed block life insurance issuance in a continuous unrealized loss position for twelve months or longer. + References No definition available. + Details
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- Definition Aggregate losses for an issuance of a large diversified financial services company that is in a continuous unrealized loss position for twelve months or longer. + References No definition available. + Details
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- Definition Aggregate losses for Alt-A securities that are in a continuous unrealized loss position for twelve months or longer. + References No definition available. + Details
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- Definition Number of Alt-A securities in a continuous unrealized loss position greater than twelve months. + References No definition available. + Details
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- Definition Percentage of unrealized losses on mortgage-backed securities attributable to Alt-A securities. + References No definition available. + Details
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- Definition Aggregate losses for related to a security that is secured by IRS facility lease payments in a continuous unrealized loss position for twelve months or longer. + References No definition available. + Details
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- Definition Aggregate losses of below investment grade securities and non rated securities in a continuous unrealized loss position. + References No definition available. + Details
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- Definition Fair value of below investment grade securities and non rated securities in a continuous unrealized loss position. + References No definition available. + Details
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- Definition Fair value of securities deposited with governmental authorities. + References No definition available. + Details
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- Details
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- Definition Percentage of the Segregated Account of Ambac Assurance's permitted policy claims that are currently being paid in cash. + References No definition available. + Details
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- Definition Fair Value of securities held to collateralize and fund repayment of debt issued through a resecuritization transaction. + References No definition available. + Details
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- Definition Amount of the excess of amortized cost basis over fair value of securities that have been in a loss position for twelve months or longer for securities which are categorized neither as held-to-maturity nor trading securities. + References No definition available. + Details
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