Investments - Summary of Gross Unrealized Losses and Fair Values of Ambac's Available-for-Sale Investments (Detail) - Successor [Member] - USD ($) $ in Thousands	Jun. 30, 2016	Dec. 31, 2015
Schedule of Available-for-sale Securities [Line Items]
Less than 12 Months, Fair Value	$ 940,178	$ 2,281,230
Less than 12 Months, Gross Unrealized Loss	16,719	82,799
Available-for-sale Securities, Continuous Unrealized Loss Position, Twelve Months or Longer, Fair Value	783,047	463,320
Available For Sale Securities Continuous Unrealized Loss Position 12 Months Or Longer Aggregate Losses Accumulated In Investments	47,054	21,407
Available-for-sale Securities, Continuous Unrealized Loss Position, Fair Value	1,723,225	2,744,550
Available For Sale Securities Gross Unrealized Loss Accumulated In Investments	63,773	104,206
Short-Term [Member]
Schedule of Available-for-sale Securities [Line Items]
Less than 12 Months, Fair Value	0	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	0	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	940,178	2,216,675
Less than 12 Months, Gross Unrealized Loss	16,719	82,742
Available-for-sale Securities, Continuous Unrealized Loss Position, Twelve Months or Longer, Fair Value	783,047	463,320
Available For Sale Securities Continuous Unrealized Loss Position 12 Months Or Longer Aggregate Losses Accumulated In Investments	47,054	21,407
Available-for-sale Securities, Continuous Unrealized Loss Position, Fair Value	1,723,225	2,679,995
Available For Sale Securities Gross Unrealized Loss Accumulated In Investments	63,773	104,149
Fixed Income Securities [Member]
Schedule of Available-for-sale Securities [Line Items]
Less than 12 Months, Fair Value	940,178	2,206,693
Less than 12 Months, Gross Unrealized Loss	16,719	82,741
Available-for-sale Securities, Continuous Unrealized Loss Position, Twelve Months or Longer, Fair Value	783,047	463,320
Available For Sale Securities Continuous Unrealized Loss Position 12 Months Or Longer Aggregate Losses Accumulated In Investments	47,054	21,407
Available-for-sale Securities, Continuous Unrealized Loss Position, Fair Value	1,723,225	2,670,013
Available For Sale Securities Gross Unrealized Loss Accumulated In Investments	63,773	104,148
Fixed Income Securities [Member] | Municipal Bonds [Member]
Schedule of Available-for-sale Securities [Line Items]
Less than 12 Months, Fair Value	46,358	117,008
Less than 12 Months, Gross Unrealized Loss	1,444	2,070
Available-for-sale Securities, Continuous Unrealized Loss Position, Twelve Months or Longer, Fair Value	91,648	114,708
Available For Sale Securities Continuous Unrealized Loss Position 12 Months Or Longer Aggregate Losses Accumulated In Investments	2,669	6,118
Available-for-sale Securities, Continuous Unrealized Loss Position, Fair Value	138,006	231,716
Available For Sale Securities Gross Unrealized Loss Accumulated In Investments	4,113	8,188
Fixed Income Securities [Member] | Corporate Obligations [Member]
Schedule of Available-for-sale Securities [Line Items]
Less than 12 Months, Fair Value	33,756	938,916
Less than 12 Months, Gross Unrealized Loss	610	21,331
Available-for-sale Securities, Continuous Unrealized Loss Position, Twelve Months or Longer, Fair Value	63,427	92,581
Available For Sale Securities Continuous Unrealized Loss Position 12 Months Or Longer Aggregate Losses Accumulated In Investments	359	3,001
Available-for-sale Securities, Continuous Unrealized Loss Position, Fair Value	97,183	1,031,497
Available For Sale Securities Gross Unrealized Loss Accumulated In Investments	969	24,332
Fixed Income Securities [Member] | U.S. Government Obligations [Member]
Schedule of Available-for-sale Securities [Line Items]
Less than 12 Months, Fair Value	0	2,938
Less than 12 Months, Gross Unrealized Loss	0	18
Available-for-sale Securities, Continuous Unrealized Loss Position, Twelve Months or Longer, Fair Value	5,099	10,658
Available For Sale Securities Continuous Unrealized Loss Position 12 Months Or Longer Aggregate Losses Accumulated In Investments	1	170
Available-for-sale Securities, Continuous Unrealized Loss Position, Fair Value	5,099	13,596
Available For Sale Securities Gross Unrealized Loss Accumulated In Investments	1	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	4,148	4,212
Available For Sale Securities Continuous Unrealized Loss Position 12 Months Or Longer Aggregate Losses Accumulated In Investments	4	27
Available-for-sale Securities, Continuous Unrealized Loss Position, Fair Value	4,148	4,212
Available For Sale Securities Gross Unrealized Loss Accumulated In Investments	4	27
Fixed Income Securities [Member] | Residential Mortgage-Backed Securities [Member]
Schedule of Available-for-sale Securities [Line Items]
Less than 12 Months, Fair Value	413,403	584,699
Less than 12 Months, Gross Unrealized Loss	11,851	53,367
Available-for-sale Securities, Continuous Unrealized Loss Position, Twelve Months or Longer, Fair Value	548,720	213,303
Available For Sale Securities Continuous Unrealized Loss Position 12 Months Or Longer Aggregate Losses Accumulated In Investments	42,871	11,250
Available-for-sale Securities, Continuous Unrealized Loss Position, Fair Value	962,123	798,002
Available For Sale Securities Gross Unrealized Loss Accumulated In Investments	54,722	64,617
Fixed Income Securities [Member] | Collateralized Debt Obligations [Member]
Schedule of Available-for-sale Securities [Line Items]
Less than 12 Months, Fair Value	14,794	77,538
Less than 12 Months, Gross Unrealized Loss	140	1,481
Available-for-sale Securities, Continuous Unrealized Loss Position, Twelve Months or Longer, Fair Value	56,382	0
Available For Sale Securities Continuous Unrealized Loss Position 12 Months Or Longer Aggregate Losses Accumulated In Investments	1,104	0
Available-for-sale Securities, Continuous Unrealized Loss Position, Fair Value	71,176	77,538
Available For Sale Securities Gross Unrealized Loss Accumulated In Investments	1,244	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	431,661	450,690
Less than 12 Months, Gross Unrealized Loss	2,673	3,456
Available-for-sale Securities, Continuous Unrealized Loss Position, Twelve Months or Longer, Fair Value	13,623	19,274
Available For Sale Securities Continuous Unrealized Loss Position 12 Months Or Longer Aggregate Losses Accumulated In Investments	46	36
Available-for-sale Securities, Continuous Unrealized Loss Position, Fair Value	445,284	469,964
Available For Sale Securities Gross Unrealized Loss Accumulated In Investments	2,719	3,492
Fixed Income Securities [Member] | Foreign Government Debt Securities [Member]
Schedule of Available-for-sale Securities [Line Items]
Less than 12 Months, Fair Value	206	34,904
Less than 12 Months, Gross Unrealized Loss	1	1,018
Available-for-sale Securities, Continuous Unrealized Loss Position, Twelve Months or Longer, Fair Value	0	8,584
Available For Sale Securities Continuous Unrealized Loss Position 12 Months Or Longer Aggregate Losses Accumulated In Investments	0	805
Available-for-sale Securities, Continuous Unrealized Loss Position, Fair Value	206	43,488
Available For Sale Securities Gross Unrealized Loss Accumulated In Investments	1	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	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