Investments - Summary of Gross Unrealized Losses and Fair Values of Ambac's Available-for-Sale Investments (Detail) (Successor Ambac [Member], USD $) In Thousands, unless otherwise specified	Jun. 30, 2014	Dec. 31, 2013
Schedule of Available-for-sale Securities [Line Items]
Less than 12 Months, Fair Value	$ 542,908	$ 2,920,966
Less than 12 Months, Gross Unrealized Loss	11,511	116,634
Available-for-sale Securities, Continuous Unrealized Loss Position, Twelve Months or Longer, Fair Value	540,652
Available For Sale Securities Continuous Unrealized Loss Position 12 Months Or Longer Aggregate Losses Accumulated In Investments	18,831
Available-for-sale Securities, Continuous Unrealized Loss Position, Fair Value	1,083,560
Available For Sale Securities Gross Unrealized Loss Accumulated In Investments	30,342	116,634
Residential Mortgage-Backed Securities [Member]
Schedule of Available-for-sale Securities [Line Items]
Available For Sale Securities Gross Unrealized Loss Accumulated In Investments	7,376
Short-Term [Member]
Schedule of Available-for-sale Securities [Line Items]
Less than 12 Months, Fair Value	4,009	0
Less than 12 Months, Gross Unrealized Loss	1	0
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
Available-for-sale Securities, Continuous Unrealized Loss Position, Fair Value	4,009
Available For Sale Securities Gross Unrealized Loss Accumulated In Investments	1
Fixed Income Securities [Member]
Schedule of Available-for-sale Securities [Line Items]
Less than 12 Months, Fair Value	538,899	2,920,966
Less than 12 Months, Gross Unrealized Loss	11,510	116,634
Available-for-sale Securities, Continuous Unrealized Loss Position, Twelve Months or Longer, Fair Value	540,652
Available For Sale Securities Continuous Unrealized Loss Position 12 Months Or Longer Aggregate Losses Accumulated In Investments	18,831
Fixed Income Securities [Member] | Municipal Bonds [Member]
Schedule of Available-for-sale Securities [Line Items]
Less than 12 Months, Fair Value	49,581	437,683
Less than 12 Months, Gross Unrealized Loss	200	28,427
Available-for-sale Securities, Continuous Unrealized Loss Position, Twelve Months or Longer, Fair Value	205,645
Available For Sale Securities Continuous Unrealized Loss Position 12 Months Or Longer Aggregate Losses Accumulated In Investments	7,750
Fixed Income Securities [Member] | Corporate Obligations [Member]
Schedule of Available-for-sale Securities [Line Items]
Less than 12 Months, Fair Value	213,064	877,356
Less than 12 Months, Gross Unrealized Loss	1,655	23,894
Available-for-sale Securities, Continuous Unrealized Loss Position, Twelve Months or Longer, Fair Value	243,059
Available For Sale Securities Continuous Unrealized Loss Position 12 Months Or Longer Aggregate Losses Accumulated In Investments	5,883
Fixed Income Securities [Member] | Foreign Obligations [Member]
Schedule of Available-for-sale Securities [Line Items]
Less than 12 Months, Fair Value	50,394	117,905
Less than 12 Months, Gross Unrealized Loss	1,284	6,901
Available-for-sale Securities, Continuous Unrealized Loss Position, Twelve Months or Longer, Fair Value	61,621
Available For Sale Securities Continuous Unrealized Loss Position 12 Months Or Longer Aggregate Losses Accumulated In Investments	3,914
Fixed Income Securities [Member] | U.S. Government Obligations [Member]
Schedule of Available-for-sale Securities [Line Items]
Less than 12 Months, Fair Value	15,325	70,044
Less than 12 Months, Gross Unrealized Loss	824	2,176
Available-for-sale Securities, Continuous Unrealized Loss Position, Twelve Months or Longer, Fair Value	15,737
Available For Sale Securities Continuous Unrealized Loss Position 12 Months Or Longer Aggregate Losses Accumulated In Investments	1,053
Fixed Income Securities [Member] | U.S. Agency Obligations [Member]
Schedule of Available-for-sale Securities [Line Items]
Less than 12 Months, Fair Value	0	5,834
Less than 12 Months, Gross Unrealized Loss	0	70
Available-for-sale Securities, Continuous Unrealized Loss Position, Twelve Months or Longer, Fair Value	4,460
Available For Sale Securities Continuous Unrealized Loss Position 12 Months Or Longer Aggregate Losses Accumulated In Investments	41
Fixed Income Securities [Member] | Residential Mortgage-Backed Securities [Member]
Schedule of Available-for-sale Securities [Line Items]
Less than 12 Months, Fair Value	167,511	644,502
Less than 12 Months, Gross Unrealized Loss	7,186	18,105
Available-for-sale Securities, Continuous Unrealized Loss Position, Twelve Months or Longer, Fair Value	10,130
Available For Sale Securities Continuous Unrealized Loss Position 12 Months Or Longer Aggregate Losses Accumulated In Investments	190
Fixed Income Securities [Member] | Collateralized Debt Obligations [Member]
Schedule of Available-for-sale Securities [Line Items]
Less than 12 Months, Fair Value	10,055	137,685
Less than 12 Months, Gross Unrealized Loss	329	463
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
Fixed Income Securities [Member] | Other Asset-Backed Securities [Member]
Schedule of Available-for-sale Securities [Line Items]
Less than 12 Months, Fair Value	32,969	629,957
Less than 12 Months, Gross Unrealized Loss	32	36,598
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
Fixed Income Securities [Member]
Schedule of Available-for-sale Securities [Line Items]
Available For Sale Securities Gross Unrealized Loss Accumulated In Investments	30,341	116,634
Fixed Income Securities [Member] | Municipal Bonds [Member]
Schedule of Available-for-sale Securities [Line Items]
Available For Sale Securities Gross Unrealized Loss Accumulated In Investments	7,950	28,427
Fixed Income Securities [Member] | Corporate Obligations [Member]
Schedule of Available-for-sale Securities [Line Items]
Available For Sale Securities Gross Unrealized Loss Accumulated In Investments	7,538	23,894
Fixed Income Securities [Member] | U.S. Government Obligations [Member]
Schedule of Available-for-sale Securities [Line Items]
Available For Sale Securities Gross Unrealized Loss Accumulated In Investments	1,877	2,176
Fixed Income Securities [Member] | U.S. Agency Obligations [Member]
Schedule of Available-for-sale Securities [Line Items]
Available For Sale Securities Gross Unrealized Loss Accumulated In Investments	41	70
Fixed Income Securities [Member] | Residential Mortgage-Backed Securities [Member]
Schedule of Available-for-sale Securities [Line Items]
Available For Sale Securities Gross Unrealized Loss Accumulated In Investments	7,376	18,105
Fixed Income Securities [Member] | Collateralized Debt Obligations [Member]
Schedule of Available-for-sale Securities [Line Items]
Available For Sale Securities Gross Unrealized Loss Accumulated In Investments	329	463
Fixed Income Securities [Member] | Other Asset-Backed Securities [Member]
Schedule of Available-for-sale Securities [Line Items]
Available For Sale Securities Gross Unrealized Loss Accumulated In Investments	32	36,598
Fixed Income Securities [Member] | Fixed Income Securities [Member]
Schedule of Available-for-sale Securities [Line Items]
Available-for-sale Securities, Continuous Unrealized Loss Position, Fair Value	1,079,551
Fixed Income Securities [Member] | Fixed Income Securities [Member] | Municipal Bonds [Member]
Schedule of Available-for-sale Securities [Line Items]
Available-for-sale Securities, Continuous Unrealized Loss Position, Fair Value	255,226
Fixed Income Securities [Member] | Fixed Income Securities [Member] | Corporate Obligations [Member]
Schedule of Available-for-sale Securities [Line Items]
Available-for-sale Securities, Continuous Unrealized Loss Position, Fair Value	456,123
Fixed Income Securities [Member] | Fixed Income Securities [Member] | Foreign Obligations [Member]
Schedule of Available-for-sale Securities [Line Items]
Available-for-sale Securities, Continuous Unrealized Loss Position, Fair Value	112,015
Fixed Income Securities [Member] | Fixed Income Securities [Member] | U.S. Government Obligations [Member]
Schedule of Available-for-sale Securities [Line Items]
Available-for-sale Securities, Continuous Unrealized Loss Position, Fair Value	31,062
Fixed Income Securities [Member] | Fixed Income Securities [Member] | U.S. Agency Obligations [Member]
Schedule of Available-for-sale Securities [Line Items]
Available-for-sale Securities, Continuous Unrealized Loss Position, Fair Value	4,460
Fixed Income Securities [Member] | Fixed Income Securities [Member] | Residential Mortgage-Backed Securities [Member]
Schedule of Available-for-sale Securities [Line Items]
Available-for-sale Securities, Continuous Unrealized Loss Position, Fair Value	177,641
Fixed Income Securities [Member] | Fixed Income Securities [Member] | Collateralized Debt Obligations [Member]
Schedule of Available-for-sale Securities [Line Items]
Available-for-sale Securities, Continuous Unrealized Loss Position, Fair Value	10,055
Fixed Income Securities [Member] | Fixed Income Securities [Member] | Other Asset-Backed Securities [Member]
Schedule of Available-for-sale Securities [Line Items]
Available-for-sale Securities, Continuous Unrealized Loss Position, Fair Value	$ 32,969