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Investments - Summary of Gross Unrealized Losses and Fair Values of Ambac's Available-for-Sale Investments (Detail) - Successor [Member] - USD ($) $ in Thousands	Sep. 30, 2016	Dec. 31, 2015
Schedule of Available-for-sale Securities [Line Items]
Less than 12 Months, Fair Value	$ 990,704	$ 2,281,230
Less than 12 Months, Gross Unrealized Loss	13,911	82,799
Available-for-sale Securities, Continuous Unrealized Loss Position, Twelve Months or Longer, Fair Value	695,623	463,320
Available For Sale Securities Continuous Unrealized Loss Position 12 Months Or Longer Aggregate Losses Accumulated In Investments	38,746	21,407
Available-for-sale Securities, Continuous Unrealized Loss Position, Fair Value	1,686,327	2,744,550
Available For Sale Securities Gross Unrealized Loss Accumulated In Investments	52,657	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	990,704	2,216,675
Less than 12 Months, Gross Unrealized Loss	13,911	82,742
Available-for-sale Securities, Continuous Unrealized Loss Position, Twelve Months or Longer, Fair Value	695,623	463,320
Available For Sale Securities Continuous Unrealized Loss Position 12 Months Or Longer Aggregate Losses Accumulated In Investments	38,746	21,407
Available-for-sale Securities, Continuous Unrealized Loss Position, Fair Value	1,686,327	2,679,995
Available For Sale Securities Gross Unrealized Loss Accumulated In Investments	52,657	104,149
Fixed Income Securities [Member]
Schedule of Available-for-sale Securities [Line Items]
Less than 12 Months, Fair Value	990,704	2,206,693
Less than 12 Months, Gross Unrealized Loss	13,911	82,741
Available-for-sale Securities, Continuous Unrealized Loss Position, Twelve Months or Longer, Fair Value	695,623	463,320
Available For Sale Securities Continuous Unrealized Loss Position 12 Months Or Longer Aggregate Losses Accumulated In Investments	38,746	21,407
Available-for-sale Securities, Continuous Unrealized Loss Position, Fair Value	1,686,327	2,670,013
Available For Sale Securities Gross Unrealized Loss Accumulated In Investments	52,657	104,148
Fixed Income Securities [Member] | Municipal Bonds [Member]
Schedule of Available-for-sale Securities [Line Items]
Less than 12 Months, Fair Value	35,192	117,008
Less than 12 Months, Gross Unrealized Loss	1,410	2,070
Available-for-sale Securities, Continuous Unrealized Loss Position, Twelve Months or Longer, Fair Value	103,482	114,708
Available For Sale Securities Continuous Unrealized Loss Position 12 Months Or Longer Aggregate Losses Accumulated In Investments	3,341	6,118
Available-for-sale Securities, Continuous Unrealized Loss Position, Fair Value	138,674	231,716
Available For Sale Securities Gross Unrealized Loss Accumulated In Investments	4,751	8,188
Fixed Income Securities [Member] | Corporate Obligations [Member]
Schedule of Available-for-sale Securities [Line Items]
Less than 12 Months, Fair Value	201,291	938,916
Less than 12 Months, Gross Unrealized Loss	1,611	21,331
Available-for-sale Securities, Continuous Unrealized Loss Position, Twelve Months or Longer, Fair Value	9,937	92,581
Available For Sale Securities Continuous Unrealized Loss Position 12 Months Or Longer Aggregate Losses Accumulated In Investments	50	3,001
Available-for-sale Securities, Continuous Unrealized Loss Position, Fair Value	211,228	1,031,497
Available For Sale Securities Gross Unrealized Loss Accumulated In Investments	1,661	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	1,883	2,938
Less than 12 Months, Gross Unrealized Loss	18	18
Available-for-sale Securities, Continuous Unrealized Loss Position, Twelve Months or Longer, Fair Value	5,070	10,658
Available For Sale Securities Continuous Unrealized Loss Position 12 Months Or Longer Aggregate Losses Accumulated In Investments	5	170
Available-for-sale Securities, Continuous Unrealized Loss Position, Fair Value	6,953	13,596
Available For Sale Securities Gross Unrealized Loss Accumulated In Investments	23	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	4,106	4,212
Available For Sale Securities Continuous Unrealized Loss Position 12 Months Or Longer Aggregate Losses Accumulated In Investments	2	27
Available-for-sale Securities, Continuous Unrealized Loss Position, Fair Value	4,106	4,212
Available For Sale Securities Gross Unrealized Loss Accumulated In Investments	2	27
Fixed Income Securities [Member] | Residential Mortgage-Backed Securities [Member]
Schedule of Available-for-sale Securities [Line Items]
Less than 12 Months, Fair Value	388,104	584,699
Less than 12 Months, Gross Unrealized Loss	10,199	53,367
Available-for-sale Securities, Continuous Unrealized Loss Position, Twelve Months or Longer, Fair Value	517,756	213,303
Available For Sale Securities Continuous Unrealized Loss Position 12 Months Or Longer Aggregate Losses Accumulated In Investments	35,089	11,250
Available-for-sale Securities, Continuous Unrealized Loss Position, Fair Value	905,860	798,002
Available For Sale Securities Gross Unrealized Loss Accumulated In Investments	45,288	64,617
Fixed Income Securities [Member] | Collateralized Debt Obligations [Member]
Schedule of Available-for-sale Securities [Line Items]
Less than 12 Months, Fair Value	7,409	77,538
Less than 12 Months, Gross Unrealized Loss	26	1,481
Available-for-sale Securities, Continuous Unrealized Loss Position, Twelve Months or Longer, Fair Value	29,459	0
Available For Sale Securities Continuous Unrealized Loss Position 12 Months Or Longer Aggregate Losses Accumulated In Investments	233	0
Available-for-sale Securities, Continuous Unrealized Loss Position, Fair Value	36,868	77,538
Available For Sale Securities Gross Unrealized Loss Accumulated In Investments	259	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	354,221	450,690
Less than 12 Months, Gross Unrealized Loss	641	3,456
Available-for-sale Securities, Continuous Unrealized Loss Position, Twelve Months or Longer, Fair Value	25,813	19,274
Available For Sale Securities Continuous Unrealized Loss Position 12 Months Or Longer Aggregate Losses Accumulated In Investments	26	36
Available-for-sale Securities, Continuous Unrealized Loss Position, Fair Value	380,034	469,964
Available For Sale Securities Gross Unrealized Loss Accumulated In Investments	667	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	2,604	34,904
Less than 12 Months, Gross Unrealized Loss	6	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	2,604	43,488
Available For Sale Securities Gross Unrealized Loss Accumulated In Investments	6	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

X

- Definition

Amount before tax of unrealized loss in accumulated other comprehensive income (AOCI) on investments in debt and equity securities classified as available-for-sale.

+ References

Reference 1: http://www.xbrl.org/2003/role/presentationRef
-Publisher FASB
-Name Accounting Standards Codification
-Topic 320
-SubTopic 10
-Section 50
-Paragraph 2
-Subparagraph (c)
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Amount of accumulated unrealized loss on investments in debt and equity securities classified as available-for-sale that have been in a continuous loss position for twelve months or longer.

+ References

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-Publisher FASB
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