Financial Guarantee Insurance Contracts - Summary of Information Related to Policies Currently Included in Ambac's Loss Reserves or Subrogation Recoverable (Detail) - Successor [Member] $ in Thousands	12 Months Ended
	Dec. 31, 2016 USD ($) Policies	Dec. 31, 2015 USD ($) Policies	Dec. 31, 2014 USD ($)	Dec. 31, 2013 USD ($)
Schedule of Insured Financial Obligations with Credit Deterioration [Line Items]
Number of policies | Policies	282	293
Remaining weighted-average contract period (in years)	16 years	15 years
Gross insured contractual payments outstanding:
Principal	$ 13,400,162	$ 15,976,009
Interest	11,026,059	11,867,941
Total	24,426,221	27,843,950
Gross undiscounted claim liability	7,636,110	8,192,193
Discount, gross claim liability	1,305,366	1,333,663
Gross claim liability before all subrogation and before reinsurance	6,330,744	6,858,530
Less:
Gross RMBS subrogation	(1,926,165)	(2,841,291)
Discount, RMBS subrogation	19,130	11,716
Discounted RMBS subrogation, before reinsurance	(1,907,035)	(2,829,575)	$ (2,523,540)	$ (2,206,598)
Less:
Gross other subrogation	(739,471)	(1,388,070)
Discount, other subrogation	80,079	334,251
Discounted other subrogation, before reinsurance	(659,392)	(1,053,819)
Gross claim liability, net of all subrogation and discounts, before reinsurance	3,764,317	2,975,136
Less: Unearned premium reserves	(143,141)	(189,587)
Plus: Loss adjustment expenses reserves	74,862	73,264
Claim liability reported on Balance Sheet, before reinsurance	3,696,038	2,858,813
Reinsurance recoverable reported on Balance Sheet	30,418	43,999
Ceded Loss And Loss Expenses Paid Not Yet Recovered	$ (349)	$ (60)	$ (517)
I/SL [Member]
Schedule of Insured Financial Obligations with Credit Deterioration [Line Items]
Number of policies | Policies	19	33
Remaining weighted-average contract period (in years)	9 years	9 years
Gross insured contractual payments outstanding:
Principal	$ 918,456	$ 1,830,549
Interest	345,802	724,940
Total	1,264,258	2,555,489
Gross undiscounted claim liability	3,439	6,188
Discount, gross claim liability	314	515
Gross claim liability before all subrogation and before reinsurance	3,125	5,673
Less:
Gross RMBS subrogation	0	0
Discount, RMBS subrogation	0	0
Discounted RMBS subrogation, before reinsurance	0	0
Less:
Gross other subrogation	0	0
Discount, other subrogation	0	0
Discounted other subrogation, before reinsurance	0	0
Gross claim liability, net of all subrogation and discounts, before reinsurance	3,125	5,673
Less: Unearned premium reserves	(2,394)	(3,360)
Plus: Loss adjustment expenses reserves	6,621	0
Claim liability reported on Balance Sheet, before reinsurance	7,352	2,313
Reinsurance recoverable reported on Balance Sheet	$ 120	$ 642
IA [Member]
Schedule of Insured Financial Obligations with Credit Deterioration [Line Items]
Number of policies | Policies	22	14
Remaining weighted-average contract period (in years)	8 years	17 years
Gross insured contractual payments outstanding:
Principal	$ 733,036	$ 263,288
Interest	199,631	107,624
Total	932,667	370,912
Gross undiscounted claim liability	21,175	5,632
Discount, gross claim liability	1,243	652
Gross claim liability before all subrogation and before reinsurance	19,932	4,980
Less:
Gross RMBS subrogation	0	0
Discount, RMBS subrogation	0	0
Discounted RMBS subrogation, before reinsurance	0	0
Less:
Gross other subrogation	0	0
Discount, other subrogation	0	0
Discounted other subrogation, before reinsurance	0	0
Gross claim liability, net of all subrogation and discounts, before reinsurance	19,932	4,980
Less: Unearned premium reserves	(1,807)	(1,796)
Plus: Loss adjustment expenses reserves	339	66
Claim liability reported on Balance Sheet, before reinsurance	18,464	3,250
Reinsurance recoverable reported on Balance Sheet	$ 6,063	$ 880
II [Member]
Schedule of Insured Financial Obligations with Credit Deterioration [Line Items]
Number of policies | Policies	26	23
Remaining weighted-average contract period (in years)	30 years	26 years
Gross insured contractual payments outstanding:
Principal	$ 1,992,543	$ 1,912,237
Interest	7,080,969	6,834,538
Total	9,073,512	8,746,775
Gross undiscounted claim liability	547,550	173,930
Discount, gross claim liability	331,234	96,218
Gross claim liability before all subrogation and before reinsurance	216,316	77,712
Less:
Gross RMBS subrogation	0	0
Discount, RMBS subrogation	0	0
Discounted RMBS subrogation, before reinsurance	0	0
Less:
Gross other subrogation	(14,529)	(12,937)
Discount, other subrogation	6,526	3,961
Discounted other subrogation, before reinsurance	(8,003)	(8,976)
Gross claim liability, net of all subrogation and discounts, before reinsurance	208,313	68,736
Less: Unearned premium reserves	(49,578)	(48,871)
Plus: Loss adjustment expenses reserves	777	629
Claim liability reported on Balance Sheet, before reinsurance	159,512	20,494
Reinsurance recoverable reported on Balance Sheet	$ 2,737	$ 85
III [Member]
Schedule of Insured Financial Obligations with Credit Deterioration [Line Items]
Number of policies | Policies	43	63
Remaining weighted-average contract period (in years)	17 years	19 years
Gross insured contractual payments outstanding:
Principal	$ 1,779,889	$ 2,972,615
Interest	1,110,051	1,792,525
Total	2,889,940	4,765,140
Gross undiscounted claim liability	861,455	1,595,525
Discount, gross claim liability	256,108	458,805
Gross claim liability before all subrogation and before reinsurance	605,347	1,136,720
Less:
Gross RMBS subrogation	0	0
Discount, RMBS subrogation	0	0
Discounted RMBS subrogation, before reinsurance	0	0
Less:
Gross other subrogation	(118,272)	(526,957)
Discount, other subrogation	13,426	198,643
Discounted other subrogation, before reinsurance	(104,846)	(328,314)
Gross claim liability, net of all subrogation and discounts, before reinsurance	500,501	808,406
Less: Unearned premium reserves	(31,785)	(63,257)
Plus: Loss adjustment expenses reserves	11,036	15,090
Claim liability reported on Balance Sheet, before reinsurance	479,752	760,239
Reinsurance recoverable reported on Balance Sheet	$ 39,352	$ 59,503
IV [Member]
Schedule of Insured Financial Obligations with Credit Deterioration [Line Items]
Number of policies | Policies	169	157
Remaining weighted-average contract period (in years)	14 years	13 years
Gross insured contractual payments outstanding:
Principal	$ 7,926,991	$ 8,942,730
Interest	2,275,421	2,391,523
Total	10,202,412	11,334,253
Gross undiscounted claim liability	6,139,060	6,339,537
Discount, gross claim liability	710,608	770,694
Gross claim liability before all subrogation and before reinsurance	5,428,452	5,568,843
Less:
Gross RMBS subrogation	(1,926,165)	(2,841,291)
Discount, RMBS subrogation	19,130	11,716
Discounted RMBS subrogation, before reinsurance	(1,907,035)	(2,829,575)
Less:
Gross other subrogation	(593,919)	(835,078)
Discount, other subrogation	56,273	127,669
Discounted other subrogation, before reinsurance	(537,646)	(707,409)
Gross claim liability, net of all subrogation and discounts, before reinsurance	2,983,771	2,031,859
Less: Unearned premium reserves	(57,194)	(71,848)
Plus: Loss adjustment expenses reserves	56,089	57,479
Claim liability reported on Balance Sheet, before reinsurance	2,982,666	2,017,490
Reinsurance recoverable reported on Balance Sheet	$ (17,854)	$ (17,111)
V [Member]
Schedule of Insured Financial Obligations with Credit Deterioration [Line Items]
Number of policies | Policies	3	3
Remaining weighted-average contract period (in years)	5 years	6 years
Gross insured contractual payments outstanding:
Principal	$ 49,247	$ 54,590
Interest	14,185	16,791
Total	63,432	71,381
Gross undiscounted claim liability	63,431	71,381
Discount, gross claim liability	5,859	6,779
Gross claim liability before all subrogation and before reinsurance	57,572	64,602
Less:
Gross RMBS subrogation	0	0
Discount, RMBS subrogation	0	0
Discounted RMBS subrogation, before reinsurance	0	0
Less:
Gross other subrogation	(12,751)	(13,098)
Discount, other subrogation	3,854	3,978
Discounted other subrogation, before reinsurance	(8,897)	(9,120)
Gross claim liability, net of all subrogation and discounts, before reinsurance	48,675	55,482
Less: Unearned premium reserves	(383)	(455)
Plus: Loss adjustment expenses reserves	0	0
Claim liability reported on Balance Sheet, before reinsurance	48,292	55,027
Reinsurance recoverable reported on Balance Sheet	$ 0	$ 0