Fair Value Measurements - Summary of Carrying Amount and Fair Value of Ambac's Financial Assets and Liabilities (Detail) - USD ($) $ in Thousands	Dec. 31, 2015	Dec. 31, 2014	Apr. 30, 2013
Financial liabilities:
Derivative liabilities	$ 34,543	$ 73,459
Successor [Member]
Financial assets:
Fixed income securities	5,334,120	5,150,018
Short term investments	225,789	360,065
Other investments	310,600	357,016
Other assets	8,696	12,036
Financial liabilities:
Borrowings under Guaranteed Investment Agreements	100,358	160,079	$ 358,878
Long term debt, including accrued interest	1,124,950	971,116	940,313
Successor [Member] | Variable Interest Entity [Member]
Financial assets:
Loans at Carrying Amount	11,690,324	12,371,177
Financial liabilities:
Long term debt, including accrued interest	12,327,960	12,882,076	$ 15,023,038
Successor [Member] | Carrying Amount [Member]
Financial assets:
Cash	35,744	73,903
Loans at Carrying Amount		5,714
Loans	5,206
Other assets	8,696	12,036
Total financial assets	20,064,063	20,829,639
Financial liabilities:
Borrowings under Guaranteed Investment Agreements	100,358	160,079
Long term debt, including accrued interest	1,481,045	1,273,805
Liabilities for net financial guarantees written	1,990,831	2,923,652
Total financial liabilities	18,181,955	19,846,719
Successor [Member] | Carrying Amount [Member] | Variable Interest Entity [Member]
Financial assets:
Restricted cash	5,822	7,708
Loans at Carrying Amount	11,690,324	12,371,177
Financial liabilities:
Long-term debt	12,327,960	12,882,076
Successor [Member] | Carrying Amount [Member] | Futures Contracts [Member]
Financial assets:
Derivative assets	109	0
Financial liabilities:
Derivative liabilities	0	562
Successor [Member] | Carrying Amount [Member] | Credit Derivatives [Member]
Financial assets:
Derivative assets	0	2,043
Financial liabilities:
Derivative liabilities	34,543	75,502
Successor [Member] | Total Fair Value [Member]
Financial assets:
Cash	35,744	73,903
Loans	5,128	5,634
Other assets	8,696	12,036
Total financial assets	20,051,480	20,822,011
Financial liabilities:
Obligations under investment and repurchase agreements	101,400	161,821
Long term debt, including accrued interest	1,235,721	1,379,864
Liabilities for net financial guarantees written	2,325,859	4,539,000
Total financial liabilities	18,272,701	21,569,868
Successor [Member] | Total Fair Value [Member] | Variable Interest Entity [Member]
Financial assets:
Restricted cash	5,822	7,708
Loans	11,690,324	12,371,177
Financial liabilities:
Long-term debt	12,327,960	12,882,076
Successor [Member] | Total Fair Value [Member] | Futures Contracts [Member]
Financial assets:
Derivative assets	109	0
Financial liabilities:
Derivative liabilities	0	562
Successor [Member] | Total Fair Value [Member] | Credit Derivatives [Member]
Financial assets:
Derivative assets	0	2,043
Financial liabilities:
Derivative liabilities	34,543	75,502
Successor [Member] | Other Assets [Member] | Carrying Amount [Member] | Interest Rate Swaps [Member]
Financial assets:
Derivative assets	84,886	106,974
Financial liabilities:
Derivative liabilities - interest rate swaps - asset position	(52,128)	(54,666)
Successor [Member] | Other Assets [Member] | Total Fair Value [Member] | Interest Rate Swaps [Member]
Financial assets:
Derivative assets	84,886	106,974
Financial liabilities:
Derivative liabilities - interest rate swaps - asset position	(52,128)	(54,666)
Successor [Member] | Interest Rate Swaps - Liability Position [Member] | Carrying Amount [Member] | Interest Rate Swaps [Member]
Financial assets:
Derivative assets - interest rate swaps - liability position	0
Financial liabilities:
Derivative liabilities	370,943	385,546
Successor [Member] | Interest Rate Swaps - Liability Position [Member] | Carrying Amount [Member] | Interest Rate Swaps [Member] | Variable Interest Entity [Member]
Financial liabilities:
Derivative liabilities	1,965,265	2,133,268
Successor [Member] | Interest Rate Swaps - Liability Position [Member] | Carrying Amount [Member] | Currency Swaps [Member] | Variable Interest Entity [Member]
Financial liabilities:
Derivative liabilities	(36,862)	66,895
Successor [Member] | Interest Rate Swaps - Liability Position [Member] | Total Fair Value [Member] | Interest Rate Swaps [Member]
Financial assets:
Derivative assets - interest rate swaps - liability position	0
Financial liabilities:
Derivative liabilities	370,943	385,546
Successor [Member] | Interest Rate Swaps - Liability Position [Member] | Total Fair Value [Member] | Interest Rate Swaps [Member] | Variable Interest Entity [Member]
Financial liabilities:
Derivative liabilities	1,965,265	2,133,268
Successor [Member] | Interest Rate Swaps - Liability Position [Member] | Total Fair Value [Member] | Currency Swaps [Member] | Variable Interest Entity [Member]
Financial liabilities:
Derivative liabilities	(36,862)	66,895
Successor [Member] | Level 1 [Member]
Financial assets:
Cash	35,744	73,903
Loans	0	0
Other assets	0	0
Total financial assets	418,123	665,704
Financial liabilities:
Obligations under investment and repurchase agreements	0	0
Long term debt, including accrued interest	0	0
Liabilities for net financial guarantees written	0	0
Total financial liabilities	0	562
Successor [Member] | Level 1 [Member] | Variable Interest Entity [Member]
Financial assets:
Restricted cash	5,822	7,708
Loans	0	0
Financial liabilities:
Long-term debt	0	0
Successor [Member] | Level 1 [Member] | Futures Contracts [Member]
Financial assets:
Derivative assets	109	0
Financial liabilities:
Derivative liabilities	0	562
Successor [Member] | Level 1 [Member] | Credit Derivatives [Member]
Financial assets:
Derivative assets	0	0
Financial liabilities:
Derivative liabilities	0	0
Successor [Member] | Level 1 [Member] | Other Assets [Member] | Interest Rate Swaps [Member]
Financial assets:
Derivative assets	0	0
Derivative assets - interest rate swaps - liability position		0
Financial liabilities:
Derivative liabilities - interest rate swaps - asset position	0	0
Successor [Member] | Level 1 [Member] | Interest Rate Swaps - Liability Position [Member] | Interest Rate Swaps [Member]
Financial assets:
Derivative assets - interest rate swaps - liability position	0
Financial liabilities:
Derivative liabilities	0	0
Successor [Member] | Level 1 [Member] | Interest Rate Swaps - Liability Position [Member] | Interest Rate Swaps [Member] | Variable Interest Entity [Member]
Financial liabilities:
Derivative liabilities	0	0
Successor [Member] | Level 1 [Member] | Interest Rate Swaps - Liability Position [Member] | Currency Swaps [Member] | Variable Interest Entity [Member]
Financial liabilities:
Derivative liabilities	0	0
Successor [Member] | Level 2 [Member]
Financial assets:
Cash	0	0
Loans	0	0
Other assets	0	0
Total financial assets	4,775,897	4,810,711
Financial liabilities:
Obligations under investment and repurchase agreements	0	0
Long term debt, including accrued interest	132,837	0
Liabilities for net financial guarantees written	0	0
Total financial liabilities	11,400,158	14,007,568
Successor [Member] | Level 2 [Member] | Variable Interest Entity [Member]
Financial assets:
Restricted cash	0	0
Loans	0	0
Financial liabilities:
Long-term debt	9,147,790	11,618,412
Successor [Member] | Level 2 [Member] | Futures Contracts [Member]
Financial assets:
Derivative assets	0	0
Financial liabilities:
Derivative liabilities	0	0
Successor [Member] | Level 2 [Member] | Credit Derivatives [Member]
Financial assets:
Derivative assets	0	0
Financial liabilities:
Derivative liabilities	0	0
Successor [Member] | Level 2 [Member] | Other Assets [Member] | Interest Rate Swaps [Member]
Financial assets:
Derivative assets	21,848	106,974
Derivative assets - interest rate swaps - liability position		0
Financial liabilities:
Derivative liabilities - interest rate swaps - asset position	(52,128)	(54,666)
Successor [Member] | Level 2 [Member] | Interest Rate Swaps - Liability Position [Member] | Interest Rate Swaps [Member]
Financial assets:
Derivative assets - interest rate swaps - liability position	0
Financial liabilities:
Derivative liabilities	243,256	243,659
Successor [Member] | Level 2 [Member] | Interest Rate Swaps - Liability Position [Member] | Interest Rate Swaps [Member] | Variable Interest Entity [Member]
Financial liabilities:
Derivative liabilities	1,965,265	2,133,268
Successor [Member] | Level 2 [Member] | Interest Rate Swaps - Liability Position [Member] | Currency Swaps [Member] | Variable Interest Entity [Member]
Financial liabilities:
Derivative liabilities	(36,862)	66,895
Successor [Member] | Level 3 [Member]
Financial assets:
Cash	0	0
Loans	5,128	5,634
Other assets	8,696	12,036
Total financial assets	14,857,460	15,345,596
Financial liabilities:
Obligations under investment and repurchase agreements	101,400	161,821
Long term debt, including accrued interest	1,102,884	1,379,864
Liabilities for net financial guarantees written	2,325,859	4,539,000
Total financial liabilities	6,872,543	7,561,738
Successor [Member] | Level 3 [Member] | Variable Interest Entity [Member]
Financial assets:
Restricted cash	0	0
Loans	11,690,324	12,371,177
Financial liabilities:
Long-term debt	3,180,170	1,263,664
Successor [Member] | Level 3 [Member] | Futures Contracts [Member]
Financial assets:
Derivative assets	0	0
Financial liabilities:
Derivative liabilities	0	0
Successor [Member] | Level 3 [Member] | Credit Derivatives [Member]
Financial assets:
Derivative assets	0	2,043
Financial liabilities:
Derivative liabilities	34,543	75,502
Successor [Member] | Level 3 [Member] | Other Assets [Member] | Interest Rate Swaps [Member]
Financial assets:
Derivative assets	63,038	0
Derivative assets - interest rate swaps - liability position		0
Financial liabilities:
Derivative liabilities - interest rate swaps - asset position	0	0
Successor [Member] | Level 3 [Member] | Interest Rate Swaps - Liability Position [Member] | Interest Rate Swaps [Member]
Financial assets:
Derivative assets - interest rate swaps - liability position	0
Financial liabilities:
Derivative liabilities	127,687	141,887
Successor [Member] | Level 3 [Member] | Interest Rate Swaps - Liability Position [Member] | Interest Rate Swaps [Member] | Variable Interest Entity [Member]
Financial liabilities:
Derivative liabilities	0	0
Successor [Member] | Level 3 [Member] | Interest Rate Swaps - Liability Position [Member] | Currency Swaps [Member] | Variable Interest Entity [Member]
Financial liabilities:
Derivative liabilities	0	0
Successor [Member] | Municipal Bonds [Member] | Carrying Amount [Member]
Financial assets:
Fixed income securities	420,770	525,792
Successor [Member] | Municipal Bonds [Member] | Total Fair Value [Member]
Financial assets:
Fixed income securities	420,770	525,792
Successor [Member] | Municipal Bonds [Member] | Level 1 [Member]
Financial assets:
Fixed income securities	0	0
Successor [Member] | Municipal Bonds [Member] | Level 2 [Member]
Financial assets:
Fixed income securities	420,770	525,792
Successor [Member] | Municipal Bonds [Member] | Level 3 [Member]
Financial assets:
Fixed income securities	0	0
Successor [Member] | Corporate Obligations [Member] | Carrying Amount [Member]
Financial assets:
Fixed income securities	1,593,669	1,385,594
Successor [Member] | Corporate Obligations [Member] | Carrying Amount [Member] | Variable Interest Entity [Member]
Financial assets:
Fixed income securities	2,588,556	2,743,050
Successor [Member] | Corporate Obligations [Member] | Total Fair Value [Member]
Financial assets:
Fixed income securities	1,593,669	1,385,594
Successor [Member] | Corporate Obligations [Member] | Total Fair Value [Member] | Variable Interest Entity [Member]
Financial assets:
Fixed income securities	2,588,556	2,743,050
Successor [Member] | Corporate Obligations [Member] | Level 1 [Member]
Financial assets:
Fixed income securities	0	0
Successor [Member] | Corporate Obligations [Member] | Level 1 [Member] | Variable Interest Entity [Member]
Financial assets:
Fixed income securities	0	0
Successor [Member] | Corporate Obligations [Member] | Level 2 [Member]
Financial assets:
Fixed income securities	1,593,669	1,381,786
Successor [Member] | Corporate Obligations [Member] | Level 2 [Member] | Variable Interest Entity [Member]
Financial assets:
Fixed income securities	0	0
Successor [Member] | Corporate Obligations [Member] | Level 3 [Member]
Financial assets:
Fixed income securities	0	3,808
Successor [Member] | Corporate Obligations [Member] | Level 3 [Member] | Variable Interest Entity [Member]
Financial assets:
Fixed income securities	2,588,556	2,743,050
Successor [Member] | Foreign Obligations [Member] | Carrying Amount [Member]
Financial assets:
Fixed income securities	96,306	127,757
Successor [Member] | Foreign Obligations [Member] | Total Fair Value [Member]
Financial assets:
Fixed income securities	96,306	127,757
Successor [Member] | Foreign Obligations [Member] | Level 1 [Member]
Financial assets:
Fixed income securities	87,808	117,282
Successor [Member] | Foreign Obligations [Member] | Level 2 [Member]
Financial assets:
Fixed income securities	8,498	10,475
Successor [Member] | Foreign Obligations [Member] | Level 3 [Member]
Financial assets:
Fixed income securities	0	0
Successor [Member] | US Government Debt Securities [Member] | Carrying Amount [Member]
Financial assets:
Fixed income securities	26,687	42,979
Fixed income securities, pledged as collateral	64,555	64,267
Successor [Member] | US Government Debt Securities [Member] | Total Fair Value [Member]
Financial assets:
Fixed income securities	26,687	42,979
Fixed income securities, pledged as collateral	64,555	64,267
Successor [Member] | US Government Debt Securities [Member] | Level 1 [Member]
Financial assets:
Fixed income securities	26,687	42,979
Fixed income securities, pledged as collateral	64,555	64,267
Successor [Member] | US Government Debt Securities [Member] | Level 2 [Member]
Financial assets:
Fixed income securities	0	0
Fixed income securities, pledged as collateral	0	0
Successor [Member] | US Government Debt Securities [Member] | Level 3 [Member]
Financial assets:
Fixed income securities	0	0
Fixed income securities, pledged as collateral	0	0
Successor [Member] | U.S. Agency Obligations [Member] | Carrying Amount [Member]
Financial assets:
Fixed income securities	4,212	29,486
Successor [Member] | U.S. Agency Obligations [Member] | Total Fair Value [Member]
Financial assets:
Fixed income securities	4,212	29,486
Successor [Member] | U.S. Agency Obligations [Member] | Level 1 [Member]
Financial assets:
Fixed income securities	0	0
Successor [Member] | U.S. Agency Obligations [Member] | Level 2 [Member]
Financial assets:
Fixed income securities	4,212	29,486
Successor [Member] | U.S. Agency Obligations [Member] | Level 3 [Member]
Financial assets:
Fixed income securities	0	0
Successor [Member] | Residential Mortgage-Backed Securities [Member] | Carrying Amount [Member]
Financial assets:
Fixed income securities	1,977,338	1,710,955
Successor [Member] | Residential Mortgage-Backed Securities [Member] | Total Fair Value [Member]
Financial assets:
Fixed income securities	1,977,338	1,710,955
Successor [Member] | Residential Mortgage-Backed Securities [Member] | Level 1 [Member]
Financial assets:
Fixed income securities	0	0
Successor [Member] | Residential Mortgage-Backed Securities [Member] | Level 2 [Member]
Financial assets:
Fixed income securities	1,488,454	1,516,562
Successor [Member] | Residential Mortgage-Backed Securities [Member] | Level 3 [Member]
Financial assets:
Fixed income securities	488,884	194,393
Successor [Member] | Collateralized Debt Obligations [Member] | Carrying Amount [Member]
Financial assets:
Fixed income securities	84,267	21,122
Successor [Member] | Collateralized Debt Obligations [Member] | Total Fair Value [Member]
Financial assets:
Fixed income securities	84,267	21,122
Successor [Member] | Collateralized Debt Obligations [Member] | Level 1 [Member]
Financial assets:
Fixed income securities	0	0
Successor [Member] | Collateralized Debt Obligations [Member] | Level 2 [Member]
Financial assets:
Fixed income securities	84,267	21,122
Successor [Member] | Collateralized Debt Obligations [Member] | Level 3 [Member]
Financial assets:
Fixed income securities	0	0
Successor [Member] | Asset-backed Securities [Member] | Carrying Amount [Member]
Financial assets:
Fixed income securities	840,527	882,001
Successor [Member] | Asset-backed Securities [Member] | Total Fair Value [Member]
Financial assets:
Fixed income securities	840,527	882,001
Successor [Member] | Asset-backed Securities [Member] | Level 1 [Member]
Financial assets:
Fixed income securities	0	0
Successor [Member] | Asset-backed Securities [Member] | Level 2 [Member]
Financial assets:
Fixed income securities	840,527	882,001
Successor [Member] | Asset-backed Securities [Member] | Level 3 [Member]
Financial assets:
Fixed income securities	0	0
Successor [Member] | Short-Term [Member] | Carrying Amount [Member]
Financial assets:
Short term investments	225,789	360,065
Successor [Member] | Short-Term [Member] | Total Fair Value [Member]
Financial assets:
Short term investments	225,789	360,065
Successor [Member] | Short-Term [Member] | Level 1 [Member]
Financial assets:
Short term investments	197,398	359,565
Successor [Member] | Short-Term [Member] | Level 2 [Member]
Financial assets:
Short term investments	28,391	500
Successor [Member] | Short-Term [Member] | Level 3 [Member]
Financial assets:
Short term investments	0	0
Successor [Member] | Other [Member] | Carrying Amount [Member]
Financial assets:
Other investments	310,600	357,016
Successor [Member] | Other [Member] | Total Fair Value [Member]
Financial assets:
Other investments	298,095	349,468
Successor [Member] | Other [Member] | Level 1 [Member]
Financial assets:
Other investments	0	0
Successor [Member] | Other [Member] | Level 2 [Member]
Financial assets:
Other investments	285,261	336,013
Successor [Member] | Other [Member] | Level 3 [Member]
Financial assets:
Other investments	$ 12,834	$ 13,455