Derivative Instruments - Additional Information (Detail) (USD $) In Thousands, unless otherwise specified	6 Months Ended	12 Months Ended
	Jun. 30, 2014	Dec. 31, 2013 Contract	Dec. 31, 2014 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"		$ 3,040	$ 158,240
Value of obligation to return cash collateral, recorded in "Other liabilities"		690	0
Net liability fair value of all derivative instruments linked to Ambac's own credit risk		42,555	92,869
Fair value of posted assets as collateral		126,223	118,844
Credit Derivatives [Member]
Schedule Of Loans And Allowance For Loan By Class Individually And Collectively Evaluated For Impairment [Line Items]
Number of outstanding credit derivative transactions include ratings based collateral-posting triggers	None of our outstanding credit derivative transactions	None of our outstanding credit derivative transactions
Number of credit derivative contracts		4	4
Net liability fair value of credit derivative contracts		62,296	60,729
Notional value of credit derivative contracts		$ 277,881	$ 270,747