Derivative Instruments - Additional Information (Detail) $ in Thousands	Dec. 31, 2015 USD ($) Contract	Dec. 31, 2014 USD ($) Contract
Schedule Of Loans And Allowance For Loan By Class Individually And Collectively Evaluated For Impairment [Line Items]
Value of right to reclaim cash collateral and posted margin, recorded in "Other assets"	$ 165,073	$ 158,240
Net liability fair value of all derivative instruments linked to Ambac's own credit risk	95,415	92,869
Fair value of posted assets as collateral	$ 147,974	$ 118,844
Credit Derivatives [Member]
Schedule Of Loans And Allowance For Loan By Class Individually And Collectively Evaluated For Impairment [Line Items]
Number of credit derivative contracts | Contract	2	4
Net liability fair value of credit derivative contracts	$ 19,820	$ 60,729
Notional value of credit derivative contracts	$ 68,526	$ 270,747