Consolidated Balance Sheets (Successor [Member], USD $) In Thousands, unless otherwise specified	Mar. 31, 2015	Dec. 31, 2014
Assets:
Fixed income securities, at fair value (amortized cost: 2015—$4,672,886 and 2014—$4,514,878)	$ 4,865,750	$ 4,725,686
Fixed income securities pledged as collateral, at fair value (amortized cost: 2015—$64,432 and 2014—$64,378)	64,813	64,267
Short-term investments, at fair value (amortized cost: 2015—$220,980 and 2014—$360,069)	220,980	360,065
Other investments (includes 2015—$310,578 and 2014—$336,013 at fair value)	332,609	357,016
Total investments	5,484,152	5,507,034
Cash and cash equivalents	26,641	73,903
Receivable for securities	8,779	23,660
Investment income due and accrued	24,994	25,015
Premium receivables	951,999	1,000,607
Reinsurance recoverable on paid and unpaid losses	79,308	99,838
Deferred ceded premium	117,688	123,276
Subrogation recoverable	984,129	953,274
Loans	5,494	5,714
Derivative assets	113,622	109,017
Insurance intangible asset	1,347,295	1,410,920
Goodwill	514,511	514,511
Other assets	221,252	186,985
Total assets	25,386,610	25,159,864
Liabilities:
Unearned premiums	1,583,615	1,673,785
Loss and loss expense reserves	4,475,991	4,752,007
Ceded premiums payable	59,268	60,436
Obligations under investment agreements	111,967	160,079
Deferred taxes	1,905	2,079
Current taxes	2,333	5,701
Long-term debt	979,001	971,116
Accrued interest payable	322,408	304,139
Derivative liabilities	447,356	406,944
Other liabilities	56,914	63,396
Payable for securities purchased	34,559	762
Total liabilities	23,548,889	23,486,129
Stockholders’ equity:
Preferred stock, par value $0.01 per share; 20,000,000 shares authorized; issued and outstanding shares—none	0	0
Common stock, par value $0.01 per share; 130,000,000 shares authorized; issued and outstanding shares: 2015—45,006,057; 2014—45,005,932	450	450
Additional paid-in capital	189,533	189,138
Accumulated other comprehensive income	169,329	220,283
Accumulated earnings	1,204,001	989,290
Treasury stock, shares at cost: 2015—2,459; 2014—2,459	(56)	(56)
Total Ambac Financial Group, Inc. stockholders’ equity	1,563,257	1,399,105
Noncontrolling interest	274,464	274,630
Total stockholders’ equity	1,837,721	1,673,735
Total liabilities and stockholders’ equity	25,386,610	25,159,864
Variable Interest Entity [Member]
Variable interest entity assets:
Fixed income securities, at fair value	2,704,657	2,743,050
Restricted cash	6,219	7,708
Investment income due and accrued	3,783	1,284
Loans, at fair value	12,789,201	12,371,177
Other assets	2,886	2,891
Variable interest entity liabilities:
Accrued interest payable	5,768	3,268
Long-term debt, at fair value	13,341,902	12,882,076
Derivative liabilities	2,125,713	2,200,163
Other liabilities	$ 189	$ 178