Schedule II - Condensed Financial Information of Registrant (Parent Company Only) - Condensed Statements of Cash Flows (Detail) - Successor [Member] - USD ($) $ in Thousands	12 Months Ended			18 Months Ended
	Dec. 31, 2016	Dec. 31, 2015	Dec. 31, 2014	Dec. 31, 2016
Cash flows from operating activities:
Net income (loss)	$ 74,317	$ 492,694	$ 483,696
Adjustments to reconcile net income loss to net cash used in operating activities:
Accretion (Amortization) of Discounts and Premiums, Investments	(150,061)	(129,584)	(79,183)
Reorganization items	0	0	211
Other-than-temporary impairment charges	21,819	25,659	25,794
Net realized investment gains	(39,284)	(53,476)	(58,777)
Decrease in current income taxes payable	9,727	134	4,963
Share-based compensation	5,253	3,104	3,450
Investment income due and accrued	(750)	(280)	12,647
Other, net	(35,521)	89,648	157,899
Net cash provided by (used in) operating activities	843,540	91,809	(967,820)
Cash flows from investing activities:
Proceeds from matured bonds	1,317,215	1,029,026	1,402,904
Purchases of bonds	(2,574,285)	(2,374,441)	(2,937,744)
Change in short-term investments	(206,002)	134,423	(87,554)
Net cash provided by (used in) investing activities	(714,643)	(175,745)	1,271,727
Cash flows from financing activities:
Proceeds from the sale of Junior Surplus Notes of the Segregated Account	0	0	224,262
Payments for Repurchase of Warrants	2,717	5,375	0	$ 8,092
Proceeds from Warrant Exercises	2	3	16
Net Cash Provided by (Used in) Financing Activities	(69,711)	46,901	(307,111)
Cash and Cash Equivalents, Period Increase (Decrease)	55,281	(38,159)	(3,467)
Cash and cash equivalents at beginning of period	35,744	73,903	77,370
Cash and cash equivalents end of period	91,025	35,744	73,903	91,025
Cash paid during the period for:
Income taxes	21,437	16,969	4,400
Professional fees paid for services rendered in connection with the Chapter 11 proceeding	0	0	272
Ambac Financial Group, Inc Parent Company Only [Member]
Cash flows from operating activities:
Net income (loss)	74,843	493,403	484,071
Adjustments to reconcile net income loss to net cash used in operating activities:
Equity in undistributed net (income) loss of non-debtor subsidiaries	(44,393)	(421,870)	(465,860)
Accretion (Amortization) of Discounts and Premiums, Investments	(7,208)	(4,690)	4
Reorganization items	0	0	211
Other-than-temporary impairment charges	289	155	0
Net realized investment gains	7	27	46
Decrease in current income taxes payable	42,126	(71,069)	221
Share-based compensation	5,253	3,105	3,450
Investment income due and accrued	(149)	(69)	11,905
Decrease in other assets	646	992	(834)
Other, net	5,814	(4,705)	(36,628)
Net cash provided by (used in) operating activities	77,228	(4,721)	(3,414)
Cash flows from investing activities:
Proceeds from matured bonds	269,459	347,539	65,032
Purchases of bonds	(279,582)	(312,419)	(271,181)
Change in short-term investments	(18,491)	(25,143)	(14,617)
Net cash provided by (used in) investing activities	(42,287)	9,977	(220,766)
Cash flows from financing activities:
Proceeds from the sale of Junior Surplus Notes of the Segregated Account	0	0	224,262
Payments for Repurchase of Warrants	(2,717)	(5,375)	0
Proceeds from Warrant Exercises	2	3	16
Net Cash Provided by (Used in) Financing Activities	(2,715)	(5,372)	224,278
Cash and Cash Equivalents, Period Increase (Decrease)	32,226	(116)	98
Cash and cash equivalents at beginning of period	25	141	43
Cash and cash equivalents end of period	32,251	25	141	$ 32,251
Cash paid during the period for:
Income taxes	0	394	0
Professional fees paid for services rendered in connection with the Chapter 11 proceeding	$ 0	$ 0	$ 272