Fair Value Measurements - Summary of Carrying Amount and Fair Value of Ambac's Financial Assets and Liabilities (Detail) - USD ($) $ in Thousands	Jun. 30, 2016	Dec. 31, 2015
Financial assets:
Other investments	$ 383,107	$ 285,261
Other assets	8,687	8,696
Financial liabilities:
Derivative liabilities	18,207	34,543
Successor [Member]
Financial assets:
Fixed income securities	6,110,754	5,334,120
Short term investments	336,222	225,789
Successor [Member] | Total Fair Value [Member]
Financial assets:
Other investments	394,273	298,095
Cash	23,044	35,744
Loans	4,464	5,128
Total financial assets	20,303,101	20,051,480
Financial liabilities:
Obligations under investment and repurchase agreements	82,682	101,400
Liabilities for net financial guarantees written	3,873,330	2,325,859
Long-term debt	1,374,646	1,235,721
Total financial liabilities	19,273,591	18,272,701
Successor [Member] | Total Fair Value [Member] | Variable Interest Entity [Member]
Financial assets:
Restricted cash	5,461	5,822
Loans	11,074,772	11,690,324
Financial liabilities:
Long-term debt	11,444,892	12,327,960
Successor [Member] | Carrying Amount [Member]
Financial assets:
Other investments	410,727	310,600
Cash	23,044	35,744
Loans	4,615	5,206
Total financial assets	20,319,706	20,064,063
Financial liabilities:
Obligations under investment and repurchase agreements	82,358	100,358
Liabilities for net financial guarantees written	2,911,854	2,033,484
Long-term debt	1,493,020	1,481,045
Total financial liabilities	18,430,165	18,224,608
Successor [Member] | Carrying Amount [Member] | Variable Interest Entity [Member]
Financial assets:
Restricted cash	5,461	5,822
Loans	11,074,772	11,690,324
Financial liabilities:
Long-term debt	11,444,892	12,327,960
Successor [Member] | Investments Measured at NAV as a Practical Expedient [Member]
Financial assets:
Other investments	333,448	239,516
Successor [Member] | Level 1 [Member]
Financial assets:
Other investments	49,659	45,745
Cash	23,044	35,744
Loans	0	0
Total financial assets	569,597	463,868
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	1,356	0
Successor [Member] | Level 1 [Member] | Variable Interest Entity [Member]
Financial assets:
Restricted cash	5,461	5,822
Loans	0	0
Financial liabilities:
Long-term debt	0	0
Successor [Member] | Level 2 [Member]
Financial assets:
Other investments	0	0
Cash	0	0
Loans	0	0
Total financial assets	4,920,082	4,490,636
Financial liabilities:
Obligations under investment and repurchase agreements	0	0
Liabilities for net financial guarantees written	0	0
Long-term debt	1,093,436	132,837
Total financial liabilities	12,592,050	11,400,158
Successor [Member] | Level 2 [Member] | Variable Interest Entity [Member]
Financial assets:
Restricted cash	0	0
Loans	0	0
Financial liabilities:
Long-term debt	9,186,883	9,147,790
Successor [Member] | Level 3 [Member]
Financial assets:
Other investments	11,166	12,834
Cash	0	0
Loans	4,464	5,128
Total financial assets	14,479,974	14,857,460
Financial liabilities:
Obligations under investment and repurchase agreements	82,682	101,400
Liabilities for net financial guarantees written	3,873,330	2,325,859
Long-term debt	281,210	1,102,884
Total financial liabilities	6,680,185	6,872,543
Successor [Member] | Level 3 [Member] | Variable Interest Entity [Member]
Financial assets:
Restricted cash	0	0
Loans	11,074,772	11,690,324
Financial liabilities:
Long-term debt	2,258,009	3,180,170
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	104,353	84,886
Successor [Member] | Interest Rate Swaps [Member] | Carrying Amount [Member]
Financial assets:
Derivative assets	104,353	84,886
Successor [Member] | Interest Rate Swaps [Member] | Level 1 [Member]
Financial assets:
Derivative assets	0	0
Successor [Member] | Interest Rate Swaps [Member] | Level 2 [Member]
Financial assets:
Derivative assets	23,431	21,848
Successor [Member] | Interest Rate Swaps [Member] | Level 3 [Member]
Financial assets:
Derivative assets	80,922	63,038
Successor [Member] | Municipal Bonds [Member] | Total Fair Value [Member]
Financial assets:
Fixed income securities	375,652	420,770
Successor [Member] | Municipal Bonds [Member] | Carrying Amount [Member]
Financial assets:
Fixed income securities	375,652	420,770
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	375,652	420,770
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	1,730,703	1,593,669
Successor [Member] | Corporate Obligations [Member] | Total Fair Value [Member] | Variable Interest Entity [Member]
Financial assets:
Fixed income securities	2,577,293	2,588,556
Successor [Member] | Corporate Obligations [Member] | Carrying Amount [Member]
Financial assets:
Fixed income securities	1,730,703	1,593,669
Successor [Member] | Corporate Obligations [Member] | Carrying Amount [Member] | Variable Interest Entity [Member]
Financial assets:
Fixed income securities	2,577,293	2,588,556
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	1,730,703	1,593,669
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	0
Successor [Member] | Corporate Obligations [Member] | Level 3 [Member] | Variable Interest Entity [Member]
Financial assets:
Fixed income securities	2,577,293	2,588,556
Successor [Member] | Foreign Obligations [Member] | Total Fair Value [Member]
Financial assets:
Fixed income securities	75,390	96,306
Successor [Member] | Foreign Obligations [Member] | Carrying Amount [Member]
Financial assets:
Fixed income securities	75,390	96,306
Successor [Member] | Foreign Obligations [Member] | Level 1 [Member]
Financial assets:
Fixed income securities	60,649	87,808
Successor [Member] | Foreign Obligations [Member] | Level 2 [Member]
Financial assets:
Fixed income securities	14,741	8,498
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	34,369	26,687
Fixed income securities, pledged as collateral	65,068	64,555
Successor [Member] | US Government Debt Securities [Member] | Carrying Amount [Member]
Financial assets:
Fixed income securities	34,369	26,687
Fixed income securities, pledged as collateral	65,068	64,555
Successor [Member] | US Government Debt Securities [Member] | Level 1 [Member]
Financial assets:
Fixed income securities	34,369	26,687
Fixed income securities, pledged as collateral	65,068	64,555
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	4,148	4,212
Successor [Member] | U.S. Agency Obligations [Member] | Carrying Amount [Member]
Financial assets:
Fixed income securities	4,148	4,212
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	4,148	4,212
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	2,270,543	1,977,338
Successor [Member] | Residential Mortgage-Backed Securities [Member] | Carrying Amount [Member]
Financial assets:
Fixed income securities	2,270,543	1,977,338
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	1,619,693	1,488,454
Successor [Member] | Residential Mortgage-Backed Securities [Member] | Level 3 [Member]
Financial assets:
Fixed income securities	650,850	488,884
Successor [Member] | Collateralized Debt Obligations [Member] | Total Fair Value [Member]
Financial assets:
Fixed income securities	104,562	84,267
Successor [Member] | Collateralized Debt Obligations [Member] | Carrying Amount [Member]
Financial assets:
Fixed income securities	104,562	84,267
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	104,562	84,267
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	1,114,097	840,527
Successor [Member] | Asset-backed Securities [Member] | Carrying Amount [Member]
Financial assets:
Fixed income securities	1,114,097	840,527
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	1,042,277	840,527
Successor [Member] | Asset-backed Securities [Member] | Level 3 [Member]
Financial assets:
Fixed income securities	71,820	0
Successor [Member] | Short-Term [Member] | Total Fair Value [Member]
Financial assets:
Short term investments	336,222	225,789
Successor [Member] | Short-Term [Member] | Carrying Amount [Member]
Financial assets:
Short term investments	336,222	225,789
Successor [Member] | Short-Term [Member] | Level 1 [Member]
Financial assets:
Short term investments	331,347	197,398
Successor [Member] | Short-Term [Member] | Level 2 [Member]
Financial assets:
Short term investments	4,875	28,391
Successor [Member] | Short-Term [Member] | Level 3 [Member]
Financial assets:
Short term investments	0	0
Successor [Member] | Other Assets [Member] | Total Fair Value [Member]
Financial assets:
Other assets	8,687	8,696
Successor [Member] | Other Assets [Member] | Carrying Amount [Member]
Financial assets:
Other assets	8,687	8,696
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	8,687	8,696
Successor [Member] | Futures Contracts [Member] | Total Fair Value [Member]
Financial assets:
Derivative assets		109
Successor [Member] | Futures Contracts [Member] | Carrying Amount [Member]
Financial assets:
Derivative assets		109
Successor [Member] | Futures Contracts [Member] | Level 1 [Member]
Financial assets:
Derivative assets		109
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	1,356	0
Futures Contracts [Member] | Successor [Member] | Carrying Amount [Member]
Financial liabilities:
Derivative liabilities	1,356	0
Futures Contracts [Member] | Successor [Member] | Level 1 [Member]
Financial liabilities:
Derivative liabilities	1,356	0
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	(99,841)	(52,128)
Derivative liabilities	517,441	370,943
Interest Rate Swaps [Member] | Successor [Member] | Total Fair Value [Member] | Variable Interest Entity [Member]
Financial liabilities:
Derivative liabilities	2,124,045	1,965,265
Interest Rate Swaps [Member] | Successor [Member] | Carrying Amount [Member]
Financial liabilities:
Derivative liabilities - interest rate swaps - asset position	(99,841)	(52,128)
Derivative liabilities	517,441	370,943
Interest Rate Swaps [Member] | Successor [Member] | Carrying Amount [Member] | Variable Interest Entity [Member]
Financial liabilities:
Derivative liabilities	2,124,045	1,965,265
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	(99,841)	(52,128)
Derivative liabilities	350,694	243,256
Interest Rate Swaps [Member] | Successor [Member] | Level 2 [Member] | Variable Interest Entity [Member]
Financial liabilities:
Derivative liabilities	2,124,045	1,965,265
Interest Rate Swaps [Member] | Successor [Member] | Level 3 [Member]
Financial liabilities:
Derivative liabilities - interest rate swaps - asset position	0	0
Derivative liabilities	166,747	127,687
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	18,207	34,543
Credit Derivatives [Member] | Successor [Member] | Carrying Amount [Member]
Financial liabilities:
Derivative liabilities	18,207	34,543
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	18,207	34,543
Currency Swaps [Member] | Successor [Member] | Total Fair Value [Member] | Variable Interest Entity [Member]
Financial liabilities:
Derivative liabilities	(63,167)	(36,862)
Currency Swaps [Member] | Successor [Member] | Carrying Amount [Member] | Variable Interest Entity [Member]
Financial liabilities:
Derivative liabilities	(63,167)	(36,862)
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	$ (63,167)	(36,862)
Currency Swaps [Member] | Successor [Member] | Level 3 [Member] | Variable Interest Entity [Member]
Financial liabilities:
Derivative liabilities		$ 0