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	Jun. 30, 2017	Dec. 31, 2016
Variable Interest Entities [Line Items]
Maximum Exposure To Loss	$ 46,784,794	$ 48,271,212
Insurance Assets	1,192,741	1,223,037
Insurance Liabilities	4,271,069	4,261,578
Derivative Liabilities	3,053	(140,882)
Global Structured Finance [Member]
Variable Interest Entities [Line Items]
Maximum Exposure To Loss	21,021,977	22,662,741
Insurance Assets	845,212	884,450
Insurance Liabilities	3,886,625	3,902,436
Derivative Liabilities	12,026	(132,055)
Global Public Finance [Member]
Variable Interest Entities [Line Items]
Maximum Exposure To Loss	25,762,817	25,608,471
Insurance Assets	347,529	338,587
Insurance Liabilities	384,444	359,142
Derivative Liabilities	(8,973)	(8,827)
Collateralized Debt Obligations [Member] | Global Structured Finance [Member]
Variable Interest Entities [Line Items]
Maximum Exposure To Loss	453,698	761,451
Insurance Assets	188	218
Insurance Liabilities	3,155	3,319
Derivative Liabilities	(25)	(145,402)
Residential Mortgage-Backed Securities [Member] | Global Structured Finance [Member]
Variable Interest Entities [Line Items]
Maximum Exposure To Loss	14,003,635	14,859,909
Insurance Assets	692,759	725,106
Insurance Liabilities	3,169,649	3,118,892
Other Consumer Asset-Backed [Member] | Global Structured Finance [Member]
Variable Interest Entities [Line Items]
Maximum Exposure To Loss	2,320,779	2,391,604
Insurance Assets	25,356	26,758
Insurance Liabilities	329,504	302,335
Derivative Liabilities	0	0
Other Commercial Asset-Backed [Member] | Global Structured Finance [Member]
Variable Interest Entities [Line Items]
Maximum Exposure To Loss	1,515,903	1,686,256
Insurance Assets	64,285	66,277
Insurance Liabilities	64,993	64,961
Derivative Liabilities	0	0
Other [Member] | Global Structured Finance [Member]
Variable Interest Entities [Line Items]
Maximum Exposure To Loss	2,727,962	2,963,521
Insurance Assets	62,624	66,091
Insurance Liabilities	319,324	412,929
Derivative Liabilities	$ 12,051	$ 13,347