Derivative Instruments (Details Textual) (USD $) In Thousands, unless otherwise specified	3 Months Ended		6 Months Ended
	Jun. 30, 2012	Jun. 30, 2011	Jun. 30, 2012	Jun. 30, 2011	Dec. 31, 2011
Derivative Instruments (Textual) [Abstract]
Value of right to reclaim cash collateral and posted margin recorded in Other assets	$ 28,455		$ 28,455		$ 47,421
Value of obligation to return cash collateral, recorded in Other liabilities	0		0		0
Number of outstanding credit derivative transactions include ratings based collateral-posting triggers			None of our outstanding credit derivative transactions
Amount of surplus notes that may be repurchased under stand-alone derivatives	500,000		500,000
Aggregate fair value of all derivative instruments linked to Ambac's own credit risk in a net liability position	238,203		238,203		266,626
Fair value of posted assets as collateral	286,660		286,660		263,530
Call Option [Member]
Derivative Instruments [Line Items]
Maturity Date of call options			Jun. 01, 2012
Call option asset position					6,055
Gains in change in fair value of the call options	39,030	4,045	100,710	20,770
Credit Derivatives [Member]
Derivative Instruments [Line Items]
Number of credit derivative contracts	4		4		4
Net liability fair value of credit derivative contracts	59,423		59,423		46,056
Notional value of credit derivative contracts	290,186		290,186		290,007
CLOs [Member]
Derivative Instruments [Line Items]
Number of credit derivatives transactions not written on a pay-as-you-go basis	6		6
Net credit derivative liabilities not written on pay as you go basis at fair value	252		252
Gross principal notional outstanding, credit derivatives not written on pay as you go basis			$ 148,273