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	Dec. 31, 2016	Dec. 31, 2015
Variable Interest Entities [Line Items]
Maximum Exposure To Loss	$ 48,271,212	$ 56,182,335
Insurance Assets	1,223,037	1,889,722
Insurance Liabilities	4,261,578	4,202,322
Derivative Liabilities	(140,882)	(138,975)
Global Structured Finance [Member]
Variable Interest Entities [Line Items]
Maximum Exposure To Loss	22,662,741	27,595,753
Insurance Assets	884,450	1,512,310
Insurance Liabilities	3,902,436	3,775,023
Derivative Liabilities	(132,055)	(114,115)
Global Public Finance [Member]
Variable Interest Entities [Line Items]
Maximum Exposure To Loss	25,608,471	28,586,582
Insurance Assets	338,587	377,412
Insurance Liabilities	359,142	427,299
Derivative Liabilities	(8,827)	(24,860)
Collateralized Debt Obligations [Member] | Global Structured Finance [Member]
Variable Interest Entities [Line Items]
Maximum Exposure To Loss	761,451	980,935
Insurance Assets	218	264
Insurance Liabilities	3,319	3,639
Derivative Liabilities	(145,402)	(129,525)
Residential Mortgage-Backed Securities [Member] | Global Structured Finance [Member]
Variable Interest Entities [Line Items]
Maximum Exposure To Loss	14,859,909	17,081,002
Insurance Assets	725,106	1,279,650
Insurance Liabilities	3,118,892	2,680,739
Other Consumer Asset-Backed [Member] | Global Structured Finance [Member]
Variable Interest Entities [Line Items]
Maximum Exposure To Loss	2,391,604	3,853,443
Insurance Assets	26,758	47,346
Insurance Liabilities	302,335	535,090
Derivative Liabilities	0	0
Other Commercial Asset-Backed [Member] | Global Structured Finance [Member]
Variable Interest Entities [Line Items]
Maximum Exposure To Loss	1,686,256	2,393,805
Insurance Assets	66,277	104,033
Insurance Liabilities	64,961	94,191
Derivative Liabilities	0	0
Other [Member] | Global Structured Finance [Member]
Variable Interest Entities [Line Items]
Maximum Exposure To Loss	2,963,521	3,286,568
Insurance Assets	66,091	81,017
Insurance Liabilities	412,929	461,364
Derivative Liabilities	$ 13,347	$ 15,410