Consolidated Balance Sheets (USD $) In Thousands, unless otherwise specified	Apr. 30, 2013	Jun. 30, 2013 Successor Ambac [Member]	Apr. 30, 2013 Successor Ambac [Member]	Jun. 30, 2013 Successor Ambac [Member] Variable Interest Entity [Member]	Apr. 30, 2013 Successor Ambac [Member] Variable Interest Entity [Member]	Apr. 30, 2013 Predecessor Ambac [Member]	Mar. 31, 2013 Predecessor Ambac [Member]	Dec. 31, 2012 Predecessor Ambac [Member]	Jun. 30, 2012 Predecessor Ambac [Member]	Dec. 31, 2011 Predecessor Ambac [Member]	Apr. 30, 2013 Predecessor Ambac [Member] Variable Interest Entity [Member]	Dec. 31, 2012 Predecessor Ambac [Member] Variable Interest Entity [Member]
Assets:
Fixed income securities, at fair value (amortized cost of $5,676,216 in 2013 and $4,751,824 in 2012)		$ 5,585,275		$ 2,242,989	$ 2,500,565			$ 5,402,395			$ 2,500,565	$ 2,261,294
Fixed income securities pledged as collateral, at fair value (amortized cost of $164,340 in 2013 and $265,517 in 2012)		164,295						265,779
Short-term investments, at fair value (amortized cost of $611,174 in 2013 and $661,219 in 2012)		611,177						661,658
Other investments, at fair value		240,417						100
Total investments		6,601,164	6,457,264			6,457,264		6,329,932
Cash		20,515	152,951			254,851		43,837
Receivable for securities		2,221	682			682		761
Investment income due and accrued		35,718	37,961	1,224	4,851	37,961		39,742			4,851	4,101
Premium receivables		1,464,898	1,531,631			1,531,631		1,620,621
Reinsurance recoverable on paid and unpaid losses		154,964	151,311			151,311		159,086
Deferred ceded premium		159,165	166,212			166,212		177,893
Subrogation recoverable		501,087	533,673			533,673		497,346
Deferred acquisition costs						184,953		199,160
Loans		7,053	7,282	13,820,878	14,752,053	8,857		9,203			14,758,077	15,568,711
Derivative assets		91,178	121,643			121,643		126,106
Current taxes		4,224	4,410
Insurance intangible asset		1,621,612	1,658,972
Goodwill	514,511	514,511	514,511
Other assets		33,738	54,821	13,222	13,972	54,821		39,715			13,972	5,467
Variable interest entity assets:
Fixed income securities, at fair value		5,585,275		2,242,989	2,500,565			5,402,395			2,500,565	2,261,294
Restricted cash				22,994	24,150						24,150	2,290
Investment income due and accrued		35,718	37,961	1,224	4,851	37,961		39,742			4,851	4,101
Loans (includes $13,820,878 and $15,359,073 at fair value)		7,053	7,282	13,820,878	14,752,053	8,857		9,203			14,758,077	15,568,711
Intangible assets				162,012	164,520						164,520
Other assets		33,738	54,821	13,222	13,972	54,821		39,715			13,972	5,467
Total assets	28,853,435	27,475,367	28,853,435			26,969,994		27,085,265
Liabilities:
Liabilities subject to compromise						1,704,641		1,704,904
Unearned premiums		2,372,807	2,482,314			2,482,314		2,778,401
Losses and loss expense reserve		6,042,649	6,106,345			6,106,345		6,619,486
Ceded premiums payable		89,435	92,468			92,468		94,527
Obligations under investment agreements		358,610	358,878			357,373		356,091
Obligations under investment repurchase agreements		5,926	5,926			5,926		5,926
Deferred taxes		1,564	1,580			1,580		1,586
Current taxes						97,490		96,778
Long-term debt		945,940	940,313	14,268,493	15,023,038	155,271		150,170			15,041,624	15,436,008
Accrued interest payable		249,387	233,876	724	4,318	252,788		228,835			4,318	3,618
Derivative liabilities		451,790	621,645	1,989,783	2,425,517	621,645		531,315			2,425,517	2,221,781
Other liabilities		86,663	90,745	6,628	6,030	88,908		102,488			6,030	293
Payable for securities purchased		42,901	27			27		25
Variable interest entity liabilities:
Accrued interest payable		249,387	233,876	724	4,318	252,788		228,835			4,318	3,618
Long-term debt (includes $14,262,734 and $15,200,538 at fair value)		945,940	940,313	14,268,493	15,023,038	155,271		150,170			15,041,624	15,436,008
Derivative liabilities		451,790	621,645	1,989,783	2,425,517	621,645		531,315			2,425,517	2,221,781
Other liabilities		86,663	90,745	6,628	6,030	88,908		102,488			6,030	293
Total liabilities	28,393,020	26,913,300	28,393,020			29,444,265		30,332,232
Stockholders' equity (deficit):
Preferred stock, value
Common stock, value		450						3,080
Additional paid-in capital		184,565						2,172,027
Accumulated other comprehensive (loss) income		(103,507)				800,260	720,071	625,385
Retained earnings (accumulated deficit)		205,681				(5,697,961)		(6,297,264)
Predecessor common stock held in treasury at cost, 5,580,657 shares at December 31, 2012						(410,695)		(410,755)
Total Ambac Financial Group, Inc. stockholders' equity (deficit)		287,189	185,000			(3,133,289)		(3,907,527)
Noncontrolling interest	275,415	274,878	275,415			659,018		660,560
Total stockholders' equity (deficit)		562,067	460,415			275,415		(3,246,967)	(3,755,379)	(3,149,533)
Total liabilities and stockholders' equity (deficit)		$ 27,475,367	$ 28,853,435			$ 26,969,994		$ 27,085,265