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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	Jun. 30, 2015	Dec. 31, 2014
Schedule of Available-for-sale Securities [Line Items]
Less than 12 Months, Fair Value	$ 2,005,174	$ 1,324,489
Less than 12 Months, Gross Unrealized Loss	67,720	20,081
Available-for-sale Securities, Continuous Unrealized Loss Position, Twelve Months or Longer, Fair Value	267,232	350,655
Available For Sale Securities Continuous Unrealized Loss Position 12 Months Or Longer Aggregate Losses Accumulated In Investments	13,382	12,188
Available-for-sale Securities, Continuous Unrealized Loss Position, Fair Value	2,272,406	1,675,144
Available For Sale Securities Gross Unrealized Loss Accumulated In Investments	81,102	32,269
Short-Term [Member]
Schedule of Available-for-sale Securities [Line Items]
Less than 12 Months, Fair Value	301	8,803
Less than 12 Months, Gross Unrealized Loss	0	4
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	301	8,803
Available For Sale Securities Gross Unrealized Loss Accumulated In Investments	0	4
Ambac Wrapped Securities [Member]
Schedule of Available-for-sale Securities [Line Items]
Available For Sale Securities Gross Unrealized Loss Accumulated In Investments	43,485
Fixed Income Investments And Other Investments [Member]
Schedule of Available-for-sale Securities [Line Items]
Less than 12 Months, Fair Value	2,005,174	1,260,222
Less than 12 Months, Gross Unrealized Loss	67,720	19,970
Available-for-sale Securities, Continuous Unrealized Loss Position, Twelve Months or Longer, Fair Value	267,232	350,655
Available For Sale Securities Continuous Unrealized Loss Position 12 Months Or Longer Aggregate Losses Accumulated In Investments	13,382	12,188
Available-for-sale Securities, Continuous Unrealized Loss Position, Fair Value	2,272,406	1,610,877
Available For Sale Securities Gross Unrealized Loss Accumulated In Investments	81,102	32,158
Fixed Income Securities [Member]
Schedule of Available-for-sale Securities [Line Items]
Less than 12 Months, Fair Value	2,004,873	1,251,419
Less than 12 Months, Gross Unrealized Loss	67,720	19,966
Available-for-sale Securities, Continuous Unrealized Loss Position, Twelve Months or Longer, Fair Value	267,232	350,655
Available For Sale Securities Continuous Unrealized Loss Position 12 Months Or Longer Aggregate Losses Accumulated In Investments	13,382	12,188
Available-for-sale Securities, Continuous Unrealized Loss Position, Fair Value	2,272,105	1,602,074
Available For Sale Securities Gross Unrealized Loss Accumulated In Investments	81,102	32,154
Fixed Income Securities [Member] | Municipal Bonds [Member]
Schedule of Available-for-sale Securities [Line Items]
Less than 12 Months, Fair Value	122,509	77,788
Less than 12 Months, Gross Unrealized Loss	2,608	1,244
Available-for-sale Securities, Continuous Unrealized Loss Position, Twelve Months or Longer, Fair Value	121,066	135,076
Available For Sale Securities Continuous Unrealized Loss Position 12 Months Or Longer Aggregate Losses Accumulated In Investments	8,263	5,752
Available-for-sale Securities, Continuous Unrealized Loss Position, Fair Value	243,575	212,864
Available For Sale Securities Gross Unrealized Loss Accumulated In Investments	10,871	6,996
Fixed Income Securities [Member] | Corporate Obligations [Member]
Schedule of Available-for-sale Securities [Line Items]
Less than 12 Months, Fair Value	808,225	453,504
Less than 12 Months, Gross Unrealized Loss	17,497	4,998
Available-for-sale Securities, Continuous Unrealized Loss Position, Twelve Months or Longer, Fair Value	96,735	172,045
Available For Sale Securities Continuous Unrealized Loss Position 12 Months Or Longer Aggregate Losses Accumulated In Investments	2,408	4,418
Available-for-sale Securities, Continuous Unrealized Loss Position, Fair Value	904,960	625,549
Available For Sale Securities Gross Unrealized Loss Accumulated In Investments	19,905	9,416
Fixed Income Securities [Member] | Foreign Obligations [Member]
Schedule of Available-for-sale Securities [Line Items]
Less than 12 Months, Fair Value	59,822	20,827
Less than 12 Months, Gross Unrealized Loss	2,395	748
Available-for-sale Securities, Continuous Unrealized Loss Position, Twelve Months or Longer, Fair Value	14,400	14,277
Available For Sale Securities Continuous Unrealized Loss Position 12 Months Or Longer Aggregate Losses Accumulated In Investments	1,737	596
Available-for-sale Securities, Continuous Unrealized Loss Position, Fair Value	74,222	35,104
Fixed Income Securities [Member] | U.S. Government Obligations [Member]
Schedule of Available-for-sale Securities [Line Items]
Less than 12 Months, Fair Value	11,534	7,223
Less than 12 Months, Gross Unrealized Loss	536	154
Available-for-sale Securities, Continuous Unrealized Loss Position, Twelve Months or Longer, Fair Value	10,739	14,735
Available For Sale Securities Continuous Unrealized Loss Position 12 Months Or Longer Aggregate Losses Accumulated In Investments	147	273
Available-for-sale Securities, Continuous Unrealized Loss Position, Fair Value	22,273	21,958
Available For Sale Securities Gross Unrealized Loss Accumulated In Investments	683	427
Fixed Income Securities [Member] | U.S. Agency Obligations [Member]
Schedule of Available-for-sale Securities [Line Items]
Less than 12 Months, Fair Value	0	25,039
Less than 12 Months, Gross Unrealized Loss	0	2
Available-for-sale Securities, Continuous Unrealized Loss Position, Twelve Months or Longer, Fair Value	4,318	4,378
Available For Sale Securities Continuous Unrealized Loss Position 12 Months Or Longer Aggregate Losses Accumulated In Investments	9	36
Available-for-sale Securities, Continuous Unrealized Loss Position, Fair Value	4,318	29,417
Available For Sale Securities Gross Unrealized Loss Accumulated In Investments	9	38
Fixed Income Securities [Member] | Residential Mortgage-Backed Securities [Member]
Schedule of Available-for-sale Securities [Line Items]
Less than 12 Months, Fair Value	840,225	413,203
Less than 12 Months, Gross Unrealized Loss	44,291	12,391
Available-for-sale Securities, Continuous Unrealized Loss Position, Twelve Months or Longer, Fair Value	10,975	10,076
Available For Sale Securities Continuous Unrealized Loss Position 12 Months Or Longer Aggregate Losses Accumulated In Investments	816	1,109
Available-for-sale Securities, Continuous Unrealized Loss Position, Fair Value	851,200	423,279
Available For Sale Securities Gross Unrealized Loss Accumulated In Investments	45,107	13,500
Fixed Income Securities [Member] | Collateralized Debt Obligations [Member]
Schedule of Available-for-sale Securities [Line Items]
Less than 12 Months, Fair Value	72,200	5,012
Less than 12 Months, Gross Unrealized Loss	329	274
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	72,200	5,012
Available For Sale Securities Gross Unrealized Loss Accumulated In Investments	329	274
Fixed Income Securities [Member] | Other Asset-Backed Securities [Member]
Schedule of Available-for-sale Securities [Line Items]
Less than 12 Months, Fair Value	90,358	248,823
Less than 12 Months, Gross Unrealized Loss	64	155
Available-for-sale Securities, Continuous Unrealized Loss Position, Twelve Months or Longer, Fair Value	8,999	68
Available For Sale Securities Continuous Unrealized Loss Position 12 Months Or Longer Aggregate Losses Accumulated In Investments	2	4
Available-for-sale Securities, Continuous Unrealized Loss Position, Fair Value	99,357	248,891
Available For Sale Securities Gross Unrealized Loss Accumulated In Investments	66	159
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	4,132	1,344
Securities Pledged as Collateral [Member] | Fixed Income Securities [Member]
Schedule of Available-for-sale Securities [Line Items]
Less than 12 Months, Fair Value	0	64,267
Less than 12 Months, Gross Unrealized Loss	0	111
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	64,267
Available For Sale Securities Gross Unrealized Loss Accumulated In Investments	0	111
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	64,267
Less than 12 Months, Gross Unrealized Loss	0	111
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	64,267
Available For Sale Securities Gross Unrealized Loss Accumulated In Investments	$ 0	$ 111

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.

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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.

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