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	6 Months Ended	12 Months Ended
	Jun. 30, 2017 USD ($) Policies	Dec. 31, 2016 USD ($) Policies	Jun. 30, 2016 USD ($)	Dec. 31, 2015 USD ($)
Schedule of Insured Financial Obligations with Credit Deterioration [Line Items]
Loss Reserves Ceded To Reinsurers	$ 47,034	$ 30,767	$ 30,108	$ 44,059
Ceded Loss And Loss Expenses Paid Not Yet Recovered	$ (568)	$ (349)	$ (1,404)
Number of policies | Policies	298	282
Remaining weighted-average contract period (in years)	16 years	16 years
Gross insured contractual payments outstanding:
Principal	$ 13,088,717	$ 13,400,162
Interest	11,370,031	11,026,059
Total	24,458,748	24,426,221
Gross undiscounted claim liability	7,704,235	7,636,110
Discount, gross claim liability	1,132,963	1,305,366
Gross claim liability before all subrogation and before reinsurance	6,571,272	6,330,744
Less:
Gross RMBS subrogation	(1,908,130)	(1,926,165)
Discount, RMBS subrogation	23,674	19,130
Discounted RMBS subrogation, before reinsurance	(1,884,456)	(1,907,035)
Less:
Gross other subrogation	(780,935)	(739,471)
Discount, other subrogation	76,109	80,079
Discounted other subrogation, before reinsurance	(704,826)	(659,392)
Gross claim liability, net of all subrogation and discounts, before reinsurance	3,981,990	3,764,317
Less: Unearned premium reserves	(146,657)	(143,141)
Plus: Loss adjustment expenses reserves	87,945	74,862
Claim liability reported on Balance Sheet, before reinsurance	3,923,278	3,696,038
Reinsurance recoverable reported on Balance Sheet	$ 46,466	$ 30,418
I/SL [Member]
Schedule of Insured Financial Obligations with Credit Deterioration [Line Items]
Number of policies | Policies	23	19
Remaining weighted-average contract period (in years)	11 years	9 years
Gross insured contractual payments outstanding:
Principal	$ 1,050,971	$ 918,456
Interest	327,175	345,802
Total	1,378,146	1,264,258
Gross undiscounted claim liability	3,845	3,439
Discount, gross claim liability	363	314
Gross claim liability before all subrogation and before reinsurance	3,482	3,125
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	3,482	3,125
Less: Unearned premium reserves	(2,114)	(2,394)
Plus: Loss adjustment expenses reserves	13,481	6,621
Claim liability reported on Balance Sheet, before reinsurance	14,849	7,352
Reinsurance recoverable reported on Balance Sheet	$ 170	$ 120
IA [Member]
Schedule of Insured Financial Obligations with Credit Deterioration [Line Items]
Number of policies | Policies	23	22
Remaining weighted-average contract period (in years)	22 years	8 years
Gross insured contractual payments outstanding:
Principal	$ 418,857	$ 733,036
Interest	376,557	199,631
Total	795,414	932,667
Gross undiscounted claim liability	33,672	21,175
Discount, gross claim liability	4,758	1,243
Gross claim liability before all subrogation and before reinsurance	28,914	19,932
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	28,914	19,932
Less: Unearned premium reserves	(6,758)	(1,807)
Plus: Loss adjustment expenses reserves	2,174	339
Claim liability reported on Balance Sheet, before reinsurance	24,330	18,464
Reinsurance recoverable reported on Balance Sheet	$ 2,697	$ 6,063
II [Member]
Schedule of Insured Financial Obligations with Credit Deterioration [Line Items]
Number of policies | Policies	33	26
Remaining weighted-average contract period (in years)	11 years	30 years
Gross insured contractual payments outstanding:
Principal	$ 1,630,620	$ 1,992,543
Interest	730,585	7,080,969
Total	2,361,205	9,073,512
Gross undiscounted claim liability	110,022	547,550
Discount, gross claim liability	19,363	331,234
Gross claim liability before all subrogation and before reinsurance	90,659	216,316
Less:
Gross RMBS subrogation	0	0
Discount, RMBS subrogation	0	0
Discounted RMBS subrogation, before reinsurance	0	0
Less:
Gross other subrogation	(18,962)	(14,529)
Discount, other subrogation	8,889	6,526
Discounted other subrogation, before reinsurance	(10,073)	(8,003)
Gross claim liability, net of all subrogation and discounts, before reinsurance	80,586	208,313
Less: Unearned premium reserves	(18,329)	(49,578)
Plus: Loss adjustment expenses reserves	331	777
Claim liability reported on Balance Sheet, before reinsurance	62,588	159,512
Reinsurance recoverable reported on Balance Sheet	$ 14,704	$ 2,737
III [Member]
Schedule of Insured Financial Obligations with Credit Deterioration [Line Items]
Number of policies | Policies	47	43
Remaining weighted-average contract period (in years)	21 years	17 years
Gross insured contractual payments outstanding:
Principal	$ 2,591,392	$ 1,779,889
Interest	7,624,470	1,110,051
Total	10,215,862	2,889,940
Gross undiscounted claim liability	1,430,192	861,455
Discount, gross claim liability	504,001	256,108
Gross claim liability before all subrogation and before reinsurance	926,191	605,347
Less:
Gross RMBS subrogation	0	0
Discount, RMBS subrogation	0	0
Discounted RMBS subrogation, before reinsurance	0	0
Less:
Gross other subrogation	(152,634)	(118,272)
Discount, other subrogation	11,529	13,426
Discounted other subrogation, before reinsurance	(141,105)	(104,846)
Gross claim liability, net of all subrogation and discounts, before reinsurance	785,086	500,501
Less: Unearned premium reserves	(61,611)	(31,785)
Plus: Loss adjustment expenses reserves	18,414	11,036
Claim liability reported on Balance Sheet, before reinsurance	741,889	479,752
Reinsurance recoverable reported on Balance Sheet	$ 45,897	$ 39,352
IV [Member]
Schedule of Insured Financial Obligations with Credit Deterioration [Line Items]
Number of policies | Policies	168	169
Remaining weighted-average contract period (in years)	13 years	14 years
Gross insured contractual payments outstanding:
Principal	$ 7,347,507	$ 7,926,991
Interest	2,293,047	2,275,421
Total	9,640,554	10,202,412
Gross undiscounted claim liability	6,058,978	6,139,060
Discount, gross claim liability	599,815	710,608
Gross claim liability before all subrogation and before reinsurance	5,459,163	5,428,452
Less:
Gross RMBS subrogation	(1,908,130)	(1,926,165)
Discount, RMBS subrogation	23,674	19,130
Discounted RMBS subrogation, before reinsurance	(1,884,456)	(1,907,035)
Less:
Gross other subrogation	(596,660)	(593,919)
Discount, other subrogation	52,126	56,273
Discounted other subrogation, before reinsurance	(544,534)	(537,646)
Gross claim liability, net of all subrogation and discounts, before reinsurance	3,030,173	2,983,771
Less: Unearned premium reserves	(57,462)	(57,194)
Plus: Loss adjustment expenses reserves	53,396	56,089
Claim liability reported on Balance Sheet, before reinsurance	3,026,107	2,982,666
Reinsurance recoverable reported on Balance Sheet	$ (17,002)	$ (17,854)
V [Member]
Schedule of Insured Financial Obligations with Credit Deterioration [Line Items]
Number of policies | Policies	4	3
Remaining weighted-average contract period (in years)	3 years	5 years
Gross insured contractual payments outstanding:
Principal	$ 49,370	$ 49,247
Interest	18,197	14,185
Total	67,567	63,432
Gross undiscounted claim liability	67,526	63,431
Discount, gross claim liability	4,663	5,859
Gross claim liability before all subrogation and before reinsurance	62,863	57,572
Less:
Gross RMBS subrogation	0	0
Discount, RMBS subrogation	0	0
Discounted RMBS subrogation, before reinsurance	0	0
Less:
Gross other subrogation	(12,679)	(12,751)
Discount, other subrogation	3,565	3,854
Discounted other subrogation, before reinsurance	(9,114)	(8,897)
Gross claim liability, net of all subrogation and discounts, before reinsurance	53,749	48,675
Less: Unearned premium reserves	(383)	(383)
Plus: Loss adjustment expenses reserves	149	0
Claim liability reported on Balance Sheet, before reinsurance	53,515	48,292
Reinsurance recoverable reported on Balance Sheet	$ 0	$ 0