Investments - Summary of Gross Unrealized Losses and Fair Values of Ambac's Available-for-Sale Investments (Detail) (USD $) In Thousands, unless otherwise specified	Mar. 31, 2014	Dec. 31, 2013
Residential Mortgage-Backed Securities [Member]
Schedule of Available-for-sale Securities [Line Items]
Less than 12 Months, Gross Unrealized Loss	$ 20,408
Other Asset-Backed Securities [Member]
Schedule of Available-for-sale Securities [Line Items]
Less than 12 Months, Gross Unrealized Loss	24,618
Successor Ambac [Member]
Schedule of Available-for-sale Securities [Line Items]
Less than 12 Months, Fair Value	2,333,756	2,920,966
Less than 12 Months, Gross Unrealized Loss	83,446	116,634
Successor Ambac [Member] | Short-Term [Member]
Schedule of Available-for-sale Securities [Line Items]
Less than 12 Months, Fair Value	1,702	0
Less than 12 Months, Gross Unrealized Loss	0	0
Successor Ambac [Member] | Fixed Income Securities [Member]
Schedule of Available-for-sale Securities [Line Items]
Less than 12 Months, Fair Value	2,332,054	2,920,966
Less than 12 Months, Gross Unrealized Loss	83,446	116,634
Successor Ambac [Member] | Fixed Income Securities [Member] | Municipal Bonds [Member]
Schedule of Available-for-sale Securities [Line Items]
Less than 12 Months, Fair Value	415,721	437,683
Less than 12 Months, Gross Unrealized Loss	16,978	28,427
Successor Ambac [Member] | Fixed Income Securities [Member] | Corporate Obligations [Member]
Schedule of Available-for-sale Securities [Line Items]
Less than 12 Months, Fair Value	738,842	877,356
Less than 12 Months, Gross Unrealized Loss	14,253	23,894
Successor Ambac [Member] | Fixed Income Securities [Member] | Foreign Obligations [Member]
Schedule of Available-for-sale Securities [Line Items]
Less than 12 Months, Fair Value	104,908	117,905
Less than 12 Months, Gross Unrealized Loss	4,818	6,901
Successor Ambac [Member] | Fixed Income Securities [Member] | U.S. Government Obligations [Member]
Schedule of Available-for-sale Securities [Line Items]
Less than 12 Months, Fair Value	29,753	70,044
Less than 12 Months, Gross Unrealized Loss	1,663	2,176
Successor Ambac [Member] | Fixed Income Securities [Member] | U.S. Agency Obligations [Member]
Schedule of Available-for-sale Securities [Line Items]
Less than 12 Months, Fair Value	31,619	5,834
Less than 12 Months, Gross Unrealized Loss	65	70
Successor Ambac [Member] | Fixed Income Securities [Member] | Residential Mortgage-Backed Securities [Member]
Schedule of Available-for-sale Securities [Line Items]
Less than 12 Months, Fair Value	441,506	644,502
Less than 12 Months, Gross Unrealized Loss	20,408	18,105
Successor Ambac [Member] | Fixed Income Securities [Member] | Collateralized Debt Obligations [Member]
Schedule of Available-for-sale Securities [Line Items]
Less than 12 Months, Fair Value	128,956	137,685
Less than 12 Months, Gross Unrealized Loss	643	463
Successor Ambac [Member] | Fixed Income Securities [Member] | Other Asset-Backed Securities [Member]
Schedule of Available-for-sale Securities [Line Items]
Less than 12 Months, Fair Value	440,749	629,957
Less than 12 Months, Gross Unrealized Loss	$ 24,618	$ 36,598