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, 2014	Dec. 31, 2013
Financial assets:
Short term investments	$ 215,103	$ 271,119
Other investments	240,530	241,069
Other assets	13,122	13,384
Financial liabilities:
Obligations under investment and repurchase agreements	359,993	359,070
Long term debt, including accrued interest	972,147	963,178
Derivative liabilities	87,715	94,322
Variable Interest Entity [Member]
Financial assets:
Loans at Carrying Amount	13,269,452	13,398,895
Financial liabilities:
Long term debt, including accrued interest	13,878,577	14,091,753
Successor Ambac [Member]
Financial assets:
Fixed income securities	6,508,915	6,282,658
Successor Ambac [Member] | Total Fair Value [Member]
Financial assets:
Cash	31,700	77,370
Loans	6,402	6,238
Other assets	13,122	13,384
Total financial assets	22,707,346	22,590,005
Financial liabilities:
Obligations under investment and repurchase agreements	362,488	360,506
Long term debt, including accrued interest	1,317,986	1,215,029
Liabilities for net financial guarantees written	5,683,120	4,876,617
Total financial liabilities	23,387,701	22,570,109
Successor Ambac [Member] | Total Fair Value [Member] | Variable Interest Entity [Member]
Financial assets:
Restricted cash	8,552	17,498
Loans	13,269,452	13,398,895
Financial liabilities:
Long-term debt	13,878,577	14,091,753
Successor Ambac [Member] | Total Fair Value [Member] | Futures Contracts [Member]
Financial assets:
Derivative assets	430	2,337
Successor Ambac [Member] | Total Fair Value [Member] | Credit Derivatives [Member]
Financial liabilities:
Derivative liabilities	87,715	94,322
Successor Ambac [Member] | Total Fair Value [Member] | Other Contracts [Member]
Financial liabilities:
Derivative liabilities	149	165
Successor Ambac [Member] | Carrying Amount [Member]
Financial assets:
Cash	31,700	77,370
Loans at Carrying Amount	6,250	6,179
Other assets	13,122	13,384
Total financial assets	22,707,194	22,589,946
Financial liabilities:
Obligations under investment and repurchase agreements	359,993	359,070
Long term debt, including accrued interest	1,288,483	1,256,602
Liabilities for net financial guarantees written	4,339,829	4,509,539
Total financial liabilities	22,012,412	22,243,168
Successor Ambac [Member] | Carrying Amount [Member] | Variable Interest Entity [Member]
Financial assets:
Restricted cash	8,552	17,498
Loans at Carrying Amount	13,269,452	13,398,895
Financial liabilities:
Long-term debt	13,878,577	14,091,753
Successor Ambac [Member] | Carrying Amount [Member] | Futures Contracts [Member]
Financial assets:
Derivative assets	430	2,337
Successor Ambac [Member] | Carrying Amount [Member] | Credit Derivatives [Member]
Financial liabilities:
Derivative liabilities	87,715	94,322
Successor Ambac [Member] | Carrying Amount [Member] | Other Contracts [Member]
Financial liabilities:
Derivative liabilities	149	165
Successor Ambac [Member] | Other Assets [Member] | Total Fair Value [Member] | Interest Rate Swaps [Member]
Financial assets:
Derivative assets	83,693	76,631
Financial liabilities:
Derivative liabilities - interest rate swaps - asset position	(50,863)	(55,619)
Successor Ambac [Member] | Other Assets [Member] | Carrying Amount [Member] | Interest Rate Swaps [Member]
Financial assets:
Derivative assets	83,693	76,631
Financial liabilities:
Derivative liabilities - interest rate swaps - asset position	(50,863)	(55,619)
Successor Ambac [Member] | Interest Rate Swaps - Liability Position [Member] | Total Fair Value [Member] | Interest Rate Swaps [Member]
Financial assets:
Derivative assets - interest rate swaps - liability position	(2,212)
Financial liabilities:
Derivative liabilities	263,839	215,030
Successor Ambac [Member] | Interest Rate Swaps - Liability Position [Member] | Total Fair Value [Member] | Interest Rate Swaps [Member] | Variable Interest Entity [Member]
Financial liabilities:
Derivative liabilities	1,758,626	1,680,834
Successor Ambac [Member] | Interest Rate Swaps - Liability Position [Member] | Total Fair Value [Member] | Currency Swaps [Member] | Variable Interest Entity [Member]
Financial liabilities:
Derivative liabilities	86,064	91,472
Successor Ambac [Member] | Interest Rate Swaps - Liability Position [Member] | Carrying Amount [Member] | Interest Rate Swaps [Member]
Financial assets:
Derivative assets - interest rate swaps - liability position	(2,212)	1,257
Financial liabilities:
Derivative liabilities	263,839	215,030
Successor Ambac [Member] | Interest Rate Swaps - Liability Position [Member] | Carrying Amount [Member] | Interest Rate Swaps [Member] | Variable Interest Entity [Member]
Financial liabilities:
Derivative liabilities	1,758,626	1,680,834
Successor Ambac [Member] | Interest Rate Swaps - Liability Position [Member] | Carrying Amount [Member] | Currency Swaps [Member] | Variable Interest Entity [Member]
Financial liabilities:
Derivative liabilities	86,064	91,472
Successor Ambac [Member] | Level 1 [Member]
Financial assets:
Cash	31,700	77,370
Loans	0	0
Total financial assets	484,249	617,288
Financial liabilities:
Total financial liabilities	0
Successor Ambac [Member] | Level 1 [Member] | Variable Interest Entity [Member]
Financial assets:
Restricted cash	8,552	17,498
Successor Ambac [Member] | Level 1 [Member] | Futures Contracts [Member]
Financial assets:
Derivative assets	430	2,337
Successor Ambac [Member] | Level 2 [Member]
Financial assets:
Cash	0	0
Loans	0	0
Total financial assets	6,320,336	6,011,135
Financial liabilities:
Total financial liabilities	14,537,231	14,416,418
Successor Ambac [Member] | Level 2 [Member] | Variable Interest Entity [Member]
Financial assets:
Loans		0
Financial liabilities:
Long-term debt	12,594,183	12,577,148
Successor Ambac [Member] | Level 2 [Member] | Other Contracts [Member]
Financial liabilities:
Derivative liabilities	149	165
Successor Ambac [Member] | Level 2 [Member] | Other Assets [Member] | Interest Rate Swaps [Member]
Financial assets:
Derivative assets	83,693	76,631
Derivative assets - interest rate swaps - liability position		1,257
Financial liabilities:
Derivative liabilities - interest rate swaps - asset position	(50,863)	(55,619)
Successor Ambac [Member] | Level 2 [Member] | Interest Rate Swaps - Liability Position [Member] | Interest Rate Swaps [Member]
Financial assets:
Derivative assets - interest rate swaps - liability position	(2,212)
Financial liabilities:
Derivative liabilities	149,072	122,418
Successor Ambac [Member] | Level 2 [Member] | Interest Rate Swaps - Liability Position [Member] | Interest Rate Swaps [Member] | Variable Interest Entity [Member]
Financial liabilities:
Derivative liabilities	1,758,626	1,680,834
Successor Ambac [Member] | Level 2 [Member] | Interest Rate Swaps - Liability Position [Member] | Currency Swaps [Member] | Variable Interest Entity [Member]
Financial liabilities:
Derivative liabilities	86,064	91,472
Successor Ambac [Member] | Level 3 [Member]
Financial assets:
Cash	0	0
Loans	6,402	6,238
Other assets	13,122	13,384
Total financial assets	15,902,761	15,961,582
Financial liabilities:
Obligations under investment and repurchase agreements	362,488	360,506
Long term debt, including accrued interest	1,317,986	1,215,029
Liabilities for net financial guarantees written	5,683,120	4,876,617
Total financial liabilities	8,850,470	8,153,691
Successor Ambac [Member] | Level 3 [Member] | Variable Interest Entity [Member]
Financial assets:
Loans	13,269,452	13,398,895
Financial liabilities:
Long-term debt	1,284,394	1,514,605
Successor Ambac [Member] | Level 3 [Member] | Credit Derivatives [Member]
Financial liabilities:
Derivative liabilities	87,715	94,322
Successor Ambac [Member] | Level 3 [Member] | Interest Rate Swaps - Liability Position [Member] | Interest Rate Swaps [Member]
Financial liabilities:
Derivative liabilities	114,767	92,612
Successor Ambac [Member] | Municipal Bonds [Member] | Total Fair Value [Member]
Financial assets:
Fixed income securities	1,185,288	1,377,723
Successor Ambac [Member] | Municipal Bonds [Member] | Carrying Amount [Member]
Financial assets:
Fixed income securities	1,185,288	1,377,723
Successor Ambac [Member] | Municipal Bonds [Member] | Level 1 [Member]
Financial assets:
Fixed income securities	0	0
Successor Ambac [Member] | Municipal Bonds [Member] | Level 2 [Member]
Financial assets:
Fixed income securities	1,185,288	1,377,723
Successor Ambac [Member] | Municipal Bonds [Member] | Level 3 [Member]
Financial assets:
Fixed income securities	0	0
Successor Ambac [Member] | Corporate Obligations [Member] | Total Fair Value [Member]
Financial assets:
Fixed income securities	1,647,584	1,489,369
Successor Ambac [Member] | Corporate Obligations [Member] | Total Fair Value [Member] | Variable Interest Entity [Member]
Financial assets:
Fixed income securities	2,546,762	2,475,182
Successor Ambac [Member] | Corporate Obligations [Member] | Carrying Amount [Member]
Financial assets:
Fixed income securities	1,647,584	1,489,369
Successor Ambac [Member] | Corporate Obligations [Member] | Carrying Amount [Member] | Variable Interest Entity [Member]
Financial assets:
Fixed income securities	2,546,762	2,475,182
Successor Ambac [Member] | Corporate Obligations [Member] | Level 1 [Member]
Financial assets:
Fixed income securities	0	0
Successor Ambac [Member] | Corporate Obligations [Member] | Level 2 [Member]
Financial assets:
Fixed income securities	1,644,028	1,485,867
Successor Ambac [Member] | Corporate Obligations [Member] | Level 3 [Member]
Financial assets:
Fixed income securities	3,556	3,502
Successor Ambac [Member] | Corporate Obligations [Member] | Level 3 [Member] | Variable Interest Entity [Member]
Financial assets:
Fixed income securities	2,546,762	2,475,182
Successor Ambac [Member] | Foreign Obligations [Member] | Total Fair Value [Member]
Financial assets:
Fixed income securities	142,044	124,877
Successor Ambac [Member] | Foreign Obligations [Member] | Carrying Amount [Member]
Financial assets:
Fixed income securities	142,044	124,877
Successor Ambac [Member] | Foreign Obligations [Member] | Level 1 [Member]
Financial assets:
Fixed income securities	0	0
Successor Ambac [Member] | Foreign Obligations [Member] | Level 2 [Member]
Financial assets:
Fixed income securities	142,044	124,877
Successor Ambac [Member] | Foreign Obligations [Member] | Level 3 [Member]
Financial assets:
Fixed income securities	0	0
Successor Ambac [Member] | US Government Debt Securities [Member] | Total Fair Value [Member]
Financial assets:
Fixed income securities	106,958	126,248
Fixed income securities, pledged as collateral	125,123	126,223
Successor Ambac [Member] | US Government Debt Securities [Member] | Carrying Amount [Member]
Financial assets:
Fixed income securities	106,958	126,248
Fixed income securities, pledged as collateral	125,123	126,223
Successor Ambac [Member] | US Government Debt Securities [Member] | Level 1 [Member]
Financial assets:
Fixed income securities	106,958	126,248
Fixed income securities, pledged as collateral	125,123	126,223
Successor Ambac [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 Ambac [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 Ambac [Member] | U.S. Agency Obligations [Member] | Total Fair Value [Member]
Financial assets:
Fixed income securities	31,825	32,154
Successor Ambac [Member] | U.S. Agency Obligations [Member] | Carrying Amount [Member]
Financial assets:
Fixed income securities	31,825	32,154
Successor Ambac [Member] | U.S. Agency Obligations [Member] | Level 1 [Member]
Financial assets:
Fixed income securities	0	0
Successor Ambac [Member] | U.S. Agency Obligations [Member] | Level 2 [Member]
Financial assets:
Fixed income securities	31,825	31,946
Successor Ambac [Member] | U.S. Agency Obligations [Member] | Level 3 [Member]
Financial assets:
Fixed income securities	0	208
Successor Ambac [Member] | Residential Mortgage-Backed Securities [Member] | Total Fair Value [Member]
Financial assets:
Fixed income securities	1,655,658	1,558,625
Successor Ambac [Member] | Residential Mortgage-Backed Securities [Member] | Carrying Amount [Member]
Financial assets:
Fixed income securities	1,655,658	1,558,625
Successor Ambac [Member] | Residential Mortgage-Backed Securities [Member] | Level 1 [Member]
Financial assets:
Fixed income securities	0	0
Successor Ambac [Member] | Residential Mortgage-Backed Securities [Member] | Level 2 [Member]
Financial assets:
Fixed income securities	1,655,658	1,558,625
Successor Ambac [Member] | Residential Mortgage-Backed Securities [Member] | Level 3 [Member]
Financial assets:
Fixed income securities	0	0
Successor Ambac [Member] | Collateralized Debt Obligations [Member] | Total Fair Value [Member]
Financial assets:
Fixed income securities	177,339	183,872
Successor Ambac [Member] | Collateralized Debt Obligations [Member] | Carrying Amount [Member]
Financial assets:
Fixed income securities	177,339	183,872
Successor Ambac [Member] | Collateralized Debt Obligations [Member] | Level 1 [Member]
Financial assets:
Fixed income securities	0	0
Successor Ambac [Member] | Collateralized Debt Obligations [Member] | Level 2 [Member]
Financial assets:
Fixed income securities	177,339	183,872
Successor Ambac [Member] | Collateralized Debt Obligations [Member] | Level 3 [Member]
Financial assets:
Fixed income securities	0	0
Successor Ambac [Member] | Asset-backed Securities [Member] | Total Fair Value [Member]
Financial assets:
Fixed income securities	1,221,993	992,448
Successor Ambac [Member] | Asset-backed Securities [Member] | Carrying Amount [Member]
Financial assets:
Fixed income securities	1,221,993	992,448
Successor Ambac [Member] | Asset-backed Securities [Member] | Level 1 [Member]
Financial assets:
Fixed income securities	0	0
Successor Ambac [Member] | Asset-backed Securities [Member] | Level 2 [Member]
Financial assets:
Fixed income securities	1,158,626	928,375
Successor Ambac [Member] | Asset-backed Securities [Member] | Level 3 [Member]
Financial assets:
Fixed income securities	63,367	64,073
Successor Ambac [Member] | Short-Term [Member] | Total Fair Value [Member]
Financial assets:
Short term investments	215,103	271,119
Successor Ambac [Member] | Short-Term [Member] | Carrying Amount [Member]
Financial assets:
Short term investments	215,103	271,119
Successor Ambac [Member] | Short-Term [Member] | Level 1 [Member]
Financial assets:
Short term investments	211,486	267,612
Successor Ambac [Member] | Short-Term [Member] | Level 2 [Member]
Financial assets:
Short term investments	3,617	3,507
Successor Ambac [Member] | Short-Term [Member] | Level 3 [Member]
Financial assets:
Short term investments	0	0
Successor Ambac [Member] | Other [Member] | Total Fair Value [Member]
Financial assets:
Other investments	240,530	241,069
Successor Ambac [Member] | Other [Member] | Carrying Amount [Member]
Financial assets:
Other investments	240,530	241,069
Successor Ambac [Member] | Other [Member] | Level 1 [Member]
Financial assets:
Other investments	0	0
Successor Ambac [Member] | Other [Member] | Level 2 [Member]
Financial assets:
Other investments	240,430	240,969
Successor Ambac [Member] | Other [Member] | Level 3 [Member]
Financial assets:
Other investments	$ 100	$ 100