Investments - Summary of Gross Unrealized Losses and Fair Values of Ambac's Available-for-Sale Investments (Detail) - Successor [Member] - USD ($) $ in Thousands	Mar. 31, 2016	Dec. 31, 2015
Schedule of Available-for-sale Securities [Line Items]
Less than 12 Months, Fair Value	$ 1,439,509	$ 2,281,230
Less than 12 Months, Gross Unrealized Loss	46,348	82,799
Available-for-sale Securities, Continuous Unrealized Loss Position, Twelve Months or Longer, Fair Value	568,791	463,320
Available For Sale Securities Continuous Unrealized Loss Position 12 Months Or Longer Aggregate Losses Accumulated In Investments	30,483	21,407
Available-for-sale Securities, Continuous Unrealized Loss Position, Fair Value	2,008,300	2,744,550
Available For Sale Securities Gross Unrealized Loss Accumulated In Investments	76,831	104,206
Short-Term [Member]
Schedule of Available-for-sale Securities [Line Items]
Less than 12 Months, Fair Value	1,983	9,982
Less than 12 Months, Gross Unrealized Loss	0	1
Available-for-sale Securities, Continuous Unrealized Loss Position, Twelve Months or Longer, Fair Value	0	0
Available For Sale Securities Continuous Unrealized Loss Position 12 Months Or Longer Aggregate Losses Accumulated In Investments	0	0
Available-for-sale Securities, Continuous Unrealized Loss Position, Fair Value	1,983	9,982
Available For Sale Securities Gross Unrealized Loss Accumulated In Investments	0	1
Fixed Income Investments And Other Investments [Member]
Schedule of Available-for-sale Securities [Line Items]
Less than 12 Months, Fair Value	1,439,509	2,216,675
Less than 12 Months, Gross Unrealized Loss	46,348	82,742
Available-for-sale Securities, Continuous Unrealized Loss Position, Twelve Months or Longer, Fair Value	568,791	463,320
Available For Sale Securities Continuous Unrealized Loss Position 12 Months Or Longer Aggregate Losses Accumulated In Investments	30,483	21,407
Available-for-sale Securities, Continuous Unrealized Loss Position, Fair Value	2,008,300	2,679,995
Available For Sale Securities Gross Unrealized Loss Accumulated In Investments	76,831	104,149
Fixed Income Securities [Member]
Schedule of Available-for-sale Securities [Line Items]
Less than 12 Months, Fair Value	1,437,526	2,206,693
Less than 12 Months, Gross Unrealized Loss	46,348	82,741
Available-for-sale Securities, Continuous Unrealized Loss Position, Twelve Months or Longer, Fair Value	568,791	463,320
Available For Sale Securities Continuous Unrealized Loss Position 12 Months Or Longer Aggregate Losses Accumulated In Investments	30,483	21,407
Available-for-sale Securities, Continuous Unrealized Loss Position, Fair Value	2,006,317	2,670,013
Available For Sale Securities Gross Unrealized Loss Accumulated In Investments	76,831	104,148
Fixed Income Securities [Member] | Municipal Bonds [Member]
Schedule of Available-for-sale Securities [Line Items]
Less than 12 Months, Fair Value	58,996	117,008
Less than 12 Months, Gross Unrealized Loss	1,587	2,070
Available-for-sale Securities, Continuous Unrealized Loss Position, Twelve Months or Longer, Fair Value	76,741	114,708
Available For Sale Securities Continuous Unrealized Loss Position 12 Months Or Longer Aggregate Losses Accumulated In Investments	3,382	6,118
Available-for-sale Securities, Continuous Unrealized Loss Position, Fair Value	135,737	231,716
Available For Sale Securities Gross Unrealized Loss Accumulated In Investments	4,969	8,188
Fixed Income Securities [Member] | Corporate Obligations [Member]
Schedule of Available-for-sale Securities [Line Items]
Less than 12 Months, Fair Value	266,795	938,916
Less than 12 Months, Gross Unrealized Loss	5,198	21,331
Available-for-sale Securities, Continuous Unrealized Loss Position, Twelve Months or Longer, Fair Value	137,811	92,581
Available For Sale Securities Continuous Unrealized Loss Position 12 Months Or Longer Aggregate Losses Accumulated In Investments	2,703	3,001
Available-for-sale Securities, Continuous Unrealized Loss Position, Fair Value	404,606	1,031,497
Available For Sale Securities Gross Unrealized Loss Accumulated In Investments	7,901	24,332
Fixed Income Securities [Member] | Foreign Obligations [Member]
Schedule of Available-for-sale Securities [Line Items]
Less than 12 Months, Fair Value	1,838	34,904
Less than 12 Months, Gross Unrealized Loss	17	1,018
Available-for-sale Securities, Continuous Unrealized Loss Position, Twelve Months or Longer, Fair Value	1,556	8,584
Available For Sale Securities Continuous Unrealized Loss Position 12 Months Or Longer Aggregate Losses Accumulated In Investments	44	805
Available-for-sale Securities, Continuous Unrealized Loss Position, Fair Value	3,394	43,488
Fixed Income Securities [Member] | U.S. Government Obligations [Member]
Schedule of Available-for-sale Securities [Line Items]
Less than 12 Months, Fair Value	7,903	2,938
Less than 12 Months, Gross Unrealized Loss	73	18
Available-for-sale Securities, Continuous Unrealized Loss Position, Twelve Months or Longer, Fair Value	8,436	10,658
Available For Sale Securities Continuous Unrealized Loss Position 12 Months Or Longer Aggregate Losses Accumulated In Investments	20	170
Available-for-sale Securities, Continuous Unrealized Loss Position, Fair Value	16,339	13,596
Available For Sale Securities Gross Unrealized Loss Accumulated In Investments	93	188
Fixed Income Securities [Member] | U.S. Agency Obligations [Member]
Schedule of Available-for-sale Securities [Line Items]
Less than 12 Months, Fair Value	0	0
Less than 12 Months, Gross Unrealized Loss	0	0
Available-for-sale Securities, Continuous Unrealized Loss Position, Twelve Months or Longer, Fair Value	4,186	4,212
Available For Sale Securities Continuous Unrealized Loss Position 12 Months Or Longer Aggregate Losses Accumulated In Investments	9	27
Available-for-sale Securities, Continuous Unrealized Loss Position, Fair Value	4,186	4,212
Available For Sale Securities Gross Unrealized Loss Accumulated In Investments	9	27
Fixed Income Securities [Member] | Residential Mortgage-Backed Securities [Member]
Schedule of Available-for-sale Securities [Line Items]
Less than 12 Months, Fair Value	624,811	584,699
Less than 12 Months, Gross Unrealized Loss	35,383	53,367
Available-for-sale Securities, Continuous Unrealized Loss Position, Twelve Months or Longer, Fair Value	304,949	213,303
Available For Sale Securities Continuous Unrealized Loss Position 12 Months Or Longer Aggregate Losses Accumulated In Investments	24,168	11,250
Available-for-sale Securities, Continuous Unrealized Loss Position, Fair Value	929,760	798,002
Available For Sale Securities Gross Unrealized Loss Accumulated In Investments	59,551	64,617
Fixed Income Securities [Member] | Collateralized Debt Obligations [Member]
Schedule of Available-for-sale Securities [Line Items]
Less than 12 Months, Fair Value	67,563	77,538
Less than 12 Months, Gross Unrealized Loss	1,550	1,481
Available-for-sale Securities, Continuous Unrealized Loss Position, Twelve Months or Longer, Fair Value	19,767	0
Available For Sale Securities Continuous Unrealized Loss Position 12 Months Or Longer Aggregate Losses Accumulated In Investments	117	0
Available-for-sale Securities, Continuous Unrealized Loss Position, Fair Value	87,330	77,538
Available For Sale Securities Gross Unrealized Loss Accumulated In Investments	1,667	1,481
Fixed Income Securities [Member] | Other Asset-Backed Securities [Member]
Schedule of Available-for-sale Securities [Line Items]
Less than 12 Months, Fair Value	409,620	450,690
Less than 12 Months, Gross Unrealized Loss	2,540	3,456
Available-for-sale Securities, Continuous Unrealized Loss Position, Twelve Months or Longer, Fair Value	15,345	19,274
Available For Sale Securities Continuous Unrealized Loss Position 12 Months Or Longer Aggregate Losses Accumulated In Investments	40	36
Available-for-sale Securities, Continuous Unrealized Loss Position, Fair Value	424,965	469,964
Available For Sale Securities Gross Unrealized Loss Accumulated In Investments	2,580	3,492
Fixed Income Securities [Member] | Foreign Government Debt Securities [Member]
Schedule of Available-for-sale Securities [Line Items]
Available For Sale Securities Gross Unrealized Loss Accumulated In Investments	61	1,823
Securities Pledged as Collateral [Member] | Fixed Income Securities [Member]
Schedule of Available-for-sale Securities [Line Items]
Less than 12 Months, Fair Value	0	64,555
Less than 12 Months, Gross Unrealized Loss	0	57
Available-for-sale Securities, Continuous Unrealized Loss Position, Twelve Months or Longer, Fair Value	0	0
Available For Sale Securities Continuous Unrealized Loss Position 12 Months Or Longer Aggregate Losses Accumulated In Investments	0	0
Available-for-sale Securities, Continuous Unrealized Loss Position, Fair Value	0	64,555
Available For Sale Securities Gross Unrealized Loss Accumulated In Investments	0	57
Securities Pledged as Collateral [Member] | Fixed Income Securities [Member] | U.S. Government Obligations [Member]
Schedule of Available-for-sale Securities [Line Items]
Less than 12 Months, Fair Value	0	64,555
Less than 12 Months, Gross Unrealized Loss	0	57
Available-for-sale Securities, Continuous Unrealized Loss Position, Twelve Months or Longer, Fair Value		0
Available For Sale Securities Continuous Unrealized Loss Position 12 Months Or Longer Aggregate Losses Accumulated In Investments	0	0
Available-for-sale Securities, Continuous Unrealized Loss Position, Fair Value	0	64,555
Available For Sale Securities Gross Unrealized Loss Accumulated In Investments	0	$ 57
Securities Pledged as Collateral [Member] | Securities Pledged as Collateral [Member] | U.S. Government Obligations [Member]
Schedule of Available-for-sale Securities [Line Items]
Available-for-sale Securities, Continuous Unrealized Loss Position, Twelve Months or Longer, Fair Value	$ 0