Special Purpose Entities, Including Variable Interest Entities - Summary of Carrying Amount of Assets, Liabilities and Maximum Exposure to Loss of Ambac's Variable Interests in Non-Consolidated Variable Interest Entities (Detail) - Variable Interest Entity [Member] - Successor [Member] - USD ($) $ in Thousands	Mar. 31, 2017	Dec. 31, 2016
Variable Interest Entities [Line Items]
Maximum Exposure To Loss	$ 47,485,188	$ 48,271,212
Insurance Assets	1,212,641	1,223,037
Insurance Liabilities	4,228,455	4,261,578
Derivative Liabilities	(144,877)	(140,882)
Global Structured Finance [Member]
Variable Interest Entities [Line Items]
Maximum Exposure To Loss	21,972,221	22,662,741
Insurance Assets	869,608	884,450
Insurance Liabilities	3,866,194	3,902,436
Derivative Liabilities	(135,802)	(132,055)
Global Public Finance [Member]
Variable Interest Entities [Line Items]
Maximum Exposure To Loss	25,512,967	25,608,471
Insurance Assets	343,033	338,587
Insurance Liabilities	362,261	359,142
Derivative Liabilities	(9,075)	(8,827)
Collateralized Debt Obligations [Member] | Global Structured Finance [Member]
Variable Interest Entities [Line Items]
Maximum Exposure To Loss	719,106	761,451
Insurance Assets	202	218
Insurance Liabilities	3,236	3,319
Derivative Liabilities	(147,064)	(145,402)
Residential Mortgage-Backed Securities [Member] | Global Structured Finance [Member]
Variable Interest Entities [Line Items]
Maximum Exposure To Loss	14,325,870	14,859,909
Insurance Assets	717,384	725,106
Insurance Liabilities	3,151,852	3,118,892
Other Consumer Asset-Backed [Member] | Global Structured Finance [Member]
Variable Interest Entities [Line Items]
Maximum Exposure To Loss	2,366,997	2,391,604
Insurance Assets	26,376	26,758
Insurance Liabilities	304,839	302,335
Derivative Liabilities	0	0
Other Commercial Asset-Backed [Member] | Global Structured Finance [Member]
Variable Interest Entities [Line Items]
Maximum Exposure To Loss	1,599,921	1,686,256
Insurance Assets	62,885	66,277
Insurance Liabilities	63,865	64,961
Derivative Liabilities	0	0
Other [Member] | Global Structured Finance [Member]
Variable Interest Entities [Line Items]
Maximum Exposure To Loss	2,960,327	2,963,521
Insurance Assets	62,761	66,091
Insurance Liabilities	342,402	412,929
Derivative Liabilities	$ 11,262	$ 13,347