Losses and Loss Expense Reserve - Summary of Information Related to Policies Currently Included in Ambac's Loss Reserves (Parenthetical) (Detail) (USD $) In Thousands, unless otherwise specified	Sep. 30, 2012	Dec. 31, 2011
Schedule of Insured Financial Obligations with Credit Deterioration [Line Items]
Loss and loss expense reserve (net of potential remediation subrogation of $1,903,348 and of $1,890,797 for the period ended Sep 2012 and Dec 2011)	$ 7,034,224	$ 7,044,070
Subrogation recoverable (includes gross potential remediation of $785,519 and of $829,469 for the period ended Sep 2012 and Dec 2011)	(514,084)	(659,810)
Liability for Claims	$ 6,520,140	$ 6,384,260

The amount needed to reflect the estimated ultimate cost of settling claims relating to financial default insured events that have occurred on or before a particular date (ordinarily, the balance sheet date) and the amount needed to provide for the estimated ultimate cost required to investigate and settle claims relating to insured events that have occurred on or before a particular date (ordinarily, the balance sheet date), whether or not reported to the insurer at that date.

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The estimated amount as of the balance sheet date to be received by an insurer from the sale of property (usually damaged) on which the insurer has paid a total claim to the insured and has obtained title to the property and the right of an insurer to pursue any course of recovery of damages, in its name or in the name of the policyholder, against a third party who is liable for costs relating to an insured event that have been paid by the insurer. Estimated salvage and subrogation is generally deducted from the liability for unpaid claims.

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