Schedule II - Reorganization Items (Detail) (USD $) In Thousands, unless otherwise specified	2 Months Ended	3 Months Ended						8 Months Ended	12 Months Ended	1 Months Ended	3 Months Ended	4 Months Ended	12 Months Ended
	Jun. 30, 2013	Dec. 31, 2014	Sep. 30, 2014	Jun. 30, 2014	Mar. 31, 2014	Dec. 31, 2013	Sep. 30, 2013	Dec. 31, 2013	Dec. 31, 2014	Apr. 30, 2013	Mar. 31, 2013	Apr. 30, 2013	Dec. 31, 2012
Reorganization Items [Line Items]
Business Acquisition, Percentage of Voting Interests Acquired										50.00%		50.00%
Successor [Member]
Reorganization Items [Line Items]
U.S. Trustee fees								$ 33	$ 7
Professional fees								460	204
Gain from cancellation and satisfaction of Predecessor Ambac debt								0	0
Fresh start reporting adjustments								0	0
Total reorganization items	424	0	2	186	23	65	4	493	211
ambc_DebtorReorganizationItemsFreshStartAdjustments								0	0
Predecessor [Member]
Reorganization Items [Line Items]
U.S. Trustee fees												23	50
Professional fees												4,483	7,165
Gain from cancellation and satisfaction of Predecessor Ambac debt												(1,521,435)	0
Fresh start reporting adjustments												(1,228,251)	0
Total reorganization items										(2,747,239)	2,059	(2,745,180)	7,215
ambc_DebtorReorganizationItemsFreshStartAdjustments												(1,228,251)	0
Ambac Financial Group, Inc Parent Company Only [Member] | Successor [Member]
Reorganization Items [Line Items]
Total reorganization items								493	211
Ambac Financial Group, Inc Parent Company Only [Member] | Predecessor [Member]
Reorganization Items [Line Items]
Total reorganization items												$ (2,745,180)	$ 7,215