Fair Value Measurements - Summary of Carrying Amount and Fair Value of Ambac's Financial Assets and Liabilities (Detail) (USD $) In Thousands, unless otherwise specified	Mar. 31, 2015	Dec. 31, 2014
Financial assets:
Other investments	$ 310,578	$ 240,969
Other assets	10,036	12,036
Financial liabilities:
Derivative liabilities	76,377	73,459
Successor [Member]
Financial assets:
Fixed income securities	5,151,543	5,150,018
Short term investments	220,980	360,065
Successor [Member] | Total Fair Value [Member]
Financial assets:
Other investments	328,187	349,468
Cash	26,641	73,903
Loans	5,476	5,634
Total financial assets	21,135,582	20,822,011
Financial liabilities:
Obligations under investment and repurchase agreements	114,438	161,821
Liabilities for net financial guarantees written	4,152,094	4,539,000
Long-term debt	1,381,938	1,379,864
Total financial liabilities	21,563,441	21,569,868
Successor [Member] | Total Fair Value [Member] | Variable Interest Entity [Member]
Financial assets:
Restricted cash	6,219	7,708
Loans	12,789,201	12,371,177
Financial liabilities:
Long-term debt	13,341,902	12,882,076
Successor [Member] | Carrying Amount [Member]
Financial assets:
Other investments	332,609	357,016
Cash	26,641	73,903
Loans	5,494	5,714
Total financial assets	21,140,022	20,829,639
Financial liabilities:
Obligations under investment and repurchase agreements	111,967	160,079
Liabilities for net financial guarantees written	2,662,701	2,923,652
Long-term debt	1,301,390	1,273,805
Total financial liabilities	19,991,029	19,846,719
Successor [Member] | Carrying Amount [Member] | Variable Interest Entity [Member]
Financial assets:
Restricted cash	6,219	7,708
Loans	12,789,201	12,371,177
Financial liabilities:
Long-term debt	13,341,902	12,882,076
Successor [Member] | Level 1 [Member]
Financial assets:
Other investments	0	0
Cash	26,641	73,903
Loans	0	0
Total financial assets	343,177	547,047
Financial liabilities:
Obligations under investment and repurchase agreements	0	0
Liabilities for net financial guarantees written	0	0
Long-term debt	0	0
Total financial liabilities	942	562
Successor [Member] | Level 1 [Member] | Variable Interest Entity [Member]
Financial assets:
Restricted cash	6,219	7,708
Loans	0	0
Financial liabilities:
Long-term debt	0	0
Successor [Member] | Level 2 [Member]
Financial assets:
Other investments	310,578	336,013
Cash	0	0
Loans	0	0
Total financial assets	5,002,694	4,929,368
Financial liabilities:
Obligations under investment and repurchase agreements	0	0
Liabilities for net financial guarantees written	0	0
Long-term debt	0	0
Total financial liabilities	13,651,729	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	11,309,803	11,618,412
Successor [Member] | Level 3 [Member]
Financial assets:
Other investments	17,609	13,455
Cash	0	0
Loans	5,476	5,634
Total financial assets	15,789,711	15,345,596
Financial liabilities:
Obligations under investment and repurchase agreements	114,438	161,821
Liabilities for net financial guarantees written	4,152,094	4,539,000
Long-term debt	1,381,938	1,379,864
Total financial liabilities	7,910,770	7,561,738
Successor [Member] | Level 3 [Member] | Variable Interest Entity [Member]
Financial assets:
Restricted cash	0	0
Loans	12,789,201	12,371,177
Financial liabilities:
Long-term debt	2,032,099	1,263,664
Successor [Member] | Level 3 [Member] | Currency Swaps [Member] | Variable Interest Entity [Member]
Financial liabilities:
Derivative liabilities	0
Successor [Member] | Interest Rate Swaps [Member] | Total Fair Value [Member]
Financial assets:
Derivative assets	113,622	106,974
Derivative assets - interest rate swaps - liability position	0
Successor [Member] | Interest Rate Swaps [Member] | Carrying Amount [Member]
Financial assets:
Derivative assets	113,622	106,974
Derivative assets - interest rate swaps - liability position	0
Successor [Member] | Interest Rate Swaps [Member] | Level 1 [Member]
Financial assets:
Derivative assets	0	0
Derivative assets - interest rate swaps - liability position	0	0
Successor [Member] | Interest Rate Swaps [Member] | Level 2 [Member]
Financial assets:
Derivative assets	113,622	106,974
Derivative assets - interest rate swaps - liability position	0	0
Successor [Member] | Interest Rate Swaps [Member] | Level 3 [Member]
Financial assets:
Derivative assets	0	0
Derivative assets - interest rate swaps - liability position	0	0
Successor [Member] | Municipal Bonds [Member] | Total Fair Value [Member]
Financial assets:
Fixed income securities	525,188	525,792
Successor [Member] | Municipal Bonds [Member] | Carrying Amount [Member]
Financial assets:
Fixed income securities	525,188	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	525,188	525,792
Successor [Member] | Municipal Bonds [Member] | Level 3 [Member]
Financial assets:
Fixed income securities	0	0
Successor [Member] | Corporate Obligations [Member] | Total Fair Value [Member]
Financial assets:
Fixed income securities	1,609,769	1,385,594
Successor [Member] | Corporate Obligations [Member] | Total Fair Value [Member] | Variable Interest Entity [Member]
Financial assets:
Fixed income securities	2,704,657	2,743,050
Successor [Member] | Corporate Obligations [Member] | Carrying Amount [Member]
Financial assets:
Fixed income securities	1,609,769	1,385,594
Successor [Member] | Corporate Obligations [Member] | Carrying Amount [Member] | Variable Interest Entity [Member]
Financial assets:
Fixed income securities	2,704,657	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	1,609,769	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	2,704,657	2,743,050
Successor [Member] | Foreign Obligations [Member] | Total Fair Value [Member]
Financial assets:
Fixed income securities	125,164	127,757
Successor [Member] | Foreign Obligations [Member] | Carrying Amount [Member]
Financial assets:
Fixed income securities	125,164	127,757
Successor [Member] | Foreign Obligations [Member] | Level 1 [Member]
Financial assets:
Fixed income securities	0	0
Successor [Member] | Foreign Obligations [Member] | Level 2 [Member]
Financial assets:
Fixed income securities	125,164	127,757
Successor [Member] | Foreign Obligations [Member] | Level 3 [Member]
Financial assets:
Fixed income securities	0	0
Successor [Member] | US Government Debt Securities [Member] | Total Fair Value [Member]
Financial assets:
Fixed income securities	30,297	42,979
Fixed income securities, pledged as collateral	64,813	64,267
Successor [Member] | US Government Debt Securities [Member] | Carrying Amount [Member]
Financial assets:
Fixed income securities	30,297	42,979
Fixed income securities, pledged as collateral	64,813	64,267
Successor [Member] | US Government Debt Securities [Member] | Level 1 [Member]
Financial assets:
Fixed income securities	30,297	42,979
Fixed income securities, pledged as collateral	64,813	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] | Total Fair Value [Member]
Financial assets:
Fixed income securities	4,427	29,486
Successor [Member] | U.S. Agency Obligations [Member] | Carrying Amount [Member]
Financial assets:
Fixed income securities	4,427	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	4,427	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] | Total Fair Value [Member]
Financial assets:
Fixed income securities	1,846,477	1,710,955
Successor [Member] | Residential Mortgage-Backed Securities [Member] | Carrying Amount [Member]
Financial assets:
Fixed income securities	1,846,477	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	1,583,745	1,516,562
Successor [Member] | Residential Mortgage-Backed Securities [Member] | Level 3 [Member]
Financial assets:
Fixed income securities	262,732	194,393
Successor [Member] | Collateralized Debt Obligations [Member] | Total Fair Value [Member]
Financial assets:
Fixed income securities	88,238	21,122
Successor [Member] | Collateralized Debt Obligations [Member] | Carrying Amount [Member]
Financial assets:
Fixed income securities	88,238	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	88,238	21,122
Successor [Member] | Collateralized Debt Obligations [Member] | Level 3 [Member]
Financial assets:
Fixed income securities	0	0
Successor [Member] | Asset-backed Securities [Member] | Total Fair Value [Member]
Financial assets:
Fixed income securities	636,190	882,001
Successor [Member] | Asset-backed Securities [Member] | Carrying Amount [Member]
Financial assets:
Fixed income securities	636,190	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	636,190	882,001
Successor [Member] | Asset-backed Securities [Member] | Level 3 [Member]
Financial assets:
Fixed income securities	0	0
Successor [Member] | Short-Term [Member] | Total Fair Value [Member]
Financial assets:
Short term investments	220,980	360,065
Successor [Member] | Short-Term [Member] | Carrying Amount [Member]
Financial assets:
Short term investments	220,980	360,065
Successor [Member] | Short-Term [Member] | Level 1 [Member]
Financial assets:
Short term investments	215,207	358,190
Successor [Member] | Short-Term [Member] | Level 2 [Member]
Financial assets:
Short term investments	5,773	1,875
Successor [Member] | Short-Term [Member] | Level 3 [Member]
Financial assets:
Short term investments	0	0
Successor [Member] | Credit Derivatives [Member] | Total Fair Value [Member]
Financial assets:
Derivative assets	0	2,043
Successor [Member] | Credit Derivatives [Member] | Carrying Amount [Member]
Financial assets:
Derivative assets	0	2,043
Successor [Member] | Credit Derivatives [Member] | Level 1 [Member]
Financial assets:
Derivative assets	0	0
Successor [Member] | Credit Derivatives [Member] | Level 2 [Member]
Financial assets:
Derivative assets	0	0
Successor [Member] | Credit Derivatives [Member] | Level 3 [Member]
Financial assets:
Derivative assets	0	2,043
Successor [Member] | Other Assets [Member] | Total Fair Value [Member]
Financial assets:
Other assets	10,036	12,036
Successor [Member] | Other Assets [Member] | Carrying Amount [Member]
Financial assets:
Other assets	10,036	12,036
Successor [Member] | Other Assets [Member] | Level 1 [Member]
Financial assets:
Other assets	0	0
Successor [Member] | Other Assets [Member] | Level 2 [Member]
Financial assets:
Other assets	0	0
Successor [Member] | Other Assets [Member] | Level 3 [Member]
Financial assets:
Other assets	10,036	12,036
Successor [Member] | Futures Contracts [Member] | Total Fair Value [Member]
Financial assets:
Derivative assets		0
Successor [Member] | Futures Contracts [Member] | Carrying Amount [Member]
Financial assets:
Derivative assets		0
Successor [Member] | Futures Contracts [Member] | Level 1 [Member]
Financial assets:
Derivative assets		0
Successor [Member] | Futures Contracts [Member] | Level 2 [Member]
Financial assets:
Derivative assets		0
Successor [Member] | Futures Contracts [Member] | Level 3 [Member]
Financial assets:
Derivative assets		0
Other Contracts [Member] | Successor [Member] | Total Fair Value [Member]
Financial liabilities:
Derivative liabilities		0
Other Contracts [Member] | Successor [Member] | Carrying Amount [Member]
Financial liabilities:
Derivative liabilities		0
Other Contracts [Member] | Successor [Member] | Level 1 [Member]
Financial liabilities:
Derivative liabilities		0
Other Contracts [Member] | Successor [Member] | Level 2 [Member]
Financial liabilities:
Derivative liabilities		0
Other Contracts [Member] | Successor [Member] | Level 3 [Member]
Financial liabilities:
Derivative liabilities		0
Futures Contracts [Member] | Successor [Member] | Total Fair Value [Member]
Financial liabilities:
Derivative liabilities	942	562
Futures Contracts [Member] | Successor [Member] | Carrying Amount [Member]
Financial liabilities:
Derivative liabilities	942	562
Futures Contracts [Member] | Successor [Member] | Level 1 [Member]
Financial liabilities:
Derivative liabilities	942	562
Futures Contracts [Member] | Successor [Member] | Level 2 [Member]
Financial liabilities:
Derivative liabilities	0	0
Futures Contracts [Member] | Successor [Member] | Level 3 [Member]
Financial liabilities:
Derivative liabilities	0	0
Interest Rate Swaps [Member] | Successor [Member] | Total Fair Value [Member]
Financial liabilities:
Derivative liabilities - interest rate swaps - asset position	(68,481)	(54,666)
Derivative liabilities	438,518	385,546
Interest Rate Swaps [Member] | Successor [Member] | Total Fair Value [Member] | Variable Interest Entity [Member]
Financial liabilities:
Derivative liabilities	2,081,082	2,133,268
Interest Rate Swaps [Member] | Successor [Member] | Carrying Amount [Member]
Financial liabilities:
Derivative liabilities - interest rate swaps - asset position	(68,481)	(54,666)
Derivative liabilities	438,518	385,546
Interest Rate Swaps [Member] | Successor [Member] | Carrying Amount [Member] | Variable Interest Entity [Member]
Financial liabilities:
Derivative liabilities	2,081,082	2,133,268
Interest Rate Swaps [Member] | Successor [Member] | Level 1 [Member]
Financial liabilities:
Derivative liabilities - interest rate swaps - asset position	0	0
Derivative liabilities	0	0
Interest Rate Swaps [Member] | Successor [Member] | Level 1 [Member] | Variable Interest Entity [Member]
Financial liabilities:
Derivative liabilities	0	0
Interest Rate Swaps [Member] | Successor [Member] | Level 2 [Member]
Financial liabilities:
Derivative liabilities - interest rate swaps - asset position	(68,481)	(54,666)
Derivative liabilities	284,694	243,659
Interest Rate Swaps [Member] | Successor [Member] | Level 2 [Member] | Variable Interest Entity [Member]
Financial liabilities:
Derivative liabilities	2,081,082	2,133,268
Interest Rate Swaps [Member] | Successor [Member] | Level 3 [Member]
Financial liabilities:
Derivative liabilities - interest rate swaps - asset position	0	0
Derivative liabilities	153,824	141,887
Interest Rate Swaps [Member] | Successor [Member] | Level 3 [Member] | Variable Interest Entity [Member]
Financial liabilities:
Derivative liabilities	0	0
Credit Derivatives [Member] | Successor [Member] | Total Fair Value [Member]
Financial liabilities:
Derivative liabilities	76,377	75,502
Credit Derivatives [Member] | Successor [Member] | Carrying Amount [Member]
Financial liabilities:
Derivative liabilities	76,377	75,502
Credit Derivatives [Member] | Successor [Member] | Level 1 [Member]
Financial liabilities:
Derivative liabilities	0	0
Credit Derivatives [Member] | Successor [Member] | Level 2 [Member]
Financial liabilities:
Derivative liabilities	0	0
Credit Derivatives [Member] | Successor [Member] | Level 3 [Member]
Financial liabilities:
Derivative liabilities	76,377	75,502
Currency Swaps [Member] | Successor [Member] | Total Fair Value [Member] | Variable Interest Entity [Member]
Financial liabilities:
Derivative liabilities	44,631	66,895
Currency Swaps [Member] | Successor [Member] | Carrying Amount [Member] | Variable Interest Entity [Member]
Financial liabilities:
Derivative liabilities	44,631	66,895
Currency Swaps [Member] | Successor [Member] | Level 1 [Member] | Variable Interest Entity [Member]
Financial liabilities:
Derivative liabilities	0	0
Currency Swaps [Member] | Successor [Member] | Level 2 [Member] | Variable Interest Entity [Member]
Financial liabilities:
Derivative liabilities	44,631	66,895
Currency Swaps [Member] | Successor [Member] | Level 3 [Member] | Variable Interest Entity [Member]
Financial liabilities:
Derivative liabilities		$ 0