Derivative Instruments - Additional Information (Detail) $ in Thousands	Dec. 31, 2016 USD ($) Contract	Dec. 31, 2015 USD ($) 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"	$ 137,701	$ 165,073
Net liability fair value of all derivative instruments linked to Ambac's own credit risk	82,944	95,415
Fair value of posted assets as collateral	$ 128,754	$ 147,974
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	2
Net liability fair value of credit derivative contracts	$ 6,123	$ 19,820
Notional value of credit derivative contracts	$ 67,783	$ 68,526