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Commitments and Contingencies - Additional Information (Detail) (USD $) | 1 Months Ended | 9 Months Ended |  |  |  |
--- | --- | --- | --- | --- | --- | ---
May 31, 2011 | Sep. 30, 2012 | Jun. 04, 2012 | Sep. 30, 2012 IRS [Member] | Feb. 24, 2012 IRS [Member] | Sep. 30, 2012 Cash [Member]
Memorandum of Understanding |  | May 4, 2011 |  |  |  |
Settlement |  | $ 24,600,000 |  | $ 100,000,000 |  | $ 2,500,000
Settlement of the claims of the putative plaintiff classes |  | 27,100,000 |  |  |  |
Ambac Assurance's payment under a swap termination surety bond |  | 4,524,000 |  |  |  |
Total par value of repurchased surplus notes |  |  | 789,000,000 |  |  |
Principal amount of surplus notes |  | 939,179,000 | 188,000,000 |  |  |
IRS claim in the Bankruptcy Court | 807,244,000 |  |  |  |  |
Payment to settle the IRS dispute and related proceedings |  | 807,244,000 |  | 1,900,000 | 1,900,000 |
Loss carry-forwards |  | $ 3,400,000 |  |  |  |
Payment by subsidiary associated with NOL Usage Tier C |  | 12.50% |  |  |  |
Payment by subsidiary associated with NOL Usage Tier D |  | 17.50% |  |  |  |

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