Consolidated Statements of Cash Flows - Successor [Member] - USD ($) $ in Thousands	12 Months Ended
	Dec. 31, 2017	Dec. 31, 2016	Dec. 31, 2015
Cash flows from operating activities:
Net income (loss) attributable to common shareholders	$ (328,715)	$ 74,843	$ 493,403
Net (loss) gain	0	526	709
Net income (loss)	(328,715)	74,317	492,694
Adjustments to reconcile net income to net cash used in operating activities:
Depreciation and amortization	992	1,220	3,215
Goodwill, Impairment Loss	0	0	514,511
Amortization of bond premium and discount	(182,997)	(150,061)	(129,584)
Share-based compensation	4,293	5,253	3,104
Deferred income taxes	31,939	(485)	126
Current income taxes	(26,272)	9,727	134
Unearned premiums, net	(168,208)	(289,140)	(372,907)
Losses and loss expenses, net	399,982	853,978	(799,399)
Ceded premiums payable	(4,653)	(10,965)	(6,942)
Investment income due and accrued	9,425	(750)	(280)
Premium receivables	76,900	172,331	174,918
Accrued interest payable	49,969	66,439	51,397
Amortization of insurance intangible assets	150,854	174,608	169,557
Net mark-to-market (gains) losses	(14,783)	(19,194)	(38,916)
Net realized investment gains	(5,366)	(39,284)	(53,476)
Other-than-temporary impairment charges	20,171	21,819	25,659
Net realized gains (losses) on extinguishment of debt	(4,920)	(4,845)	(81)
Other, net	21,538	(27,896)	80,296
Net cash provided by (used in) operating activities	(212,768)	843,540	91,809
Cash flows from investing activities:
Proceeds from sales of bonds	2,138,936	867,882	996,427
Proceeds from matured bonds	813,990	1,317,215	1,029,026
Purchases of bonds	(2,053,693)	(2,574,285)	(2,374,441)
Proceeds from sales of other invested assets	349,799	131,703	178,474
Purchases of other invested assets	(299,424)	(281,570)	(128,186)
Change in short-term investments	(126,891)	(206,002)	134,423
Loans, net	(6,198)	1,046	508
Change in cash collateral receivable	122,844	27,372	(6,833)
Other, net	(10,594)	1,996	(5,143)
Net cash provided by (used in) investing activities	928,769	(714,643)	(175,745)
Cash flows from financing activities:
Proceeds Received from a Secured Borrowing	0	0	(143,430)
Paydown Of Variable Interest Entity Secured Borrowing	28,992	29,482	13,533
Payments From Drawdowns Of Borrowings Under Guaranteed Investment Agreements	82,358	17,964	63,872
Payments for extinguishment of long-term debt	(69,499)	(19,550)	(13,752)
Payments Related to Tax Withholding for Share-based Compensation	(1,268)	0	0
Proceeds from Warrant Exercises	0	2	3
Payments for Repurchase of Warrants	0	(2,717)	(5,375)
Net Cash Provided by (Used in) Financing Activities	(182,117)	(69,711)	46,901
Effect of Exchange Rate on Cash and Cash Equivalents	(1,206)	(3,905)	(1,124)
Cash and Cash Equivalents, Period Increase (Decrease)	532,678	55,281	(38,159)
Cash and cash equivalents at beginning of period	91,025	35,744	73,903
Cash and cash equivalents end of period	623,703	91,025	35,744
Supplemental disclosure of cash flow information
Income Taxes Paid	40,334	21,437	16,969
Cash payments related to reorganization items:
Variable interest entity activities	(19,670)	14,093	(31,569)
Increase (Decrease) in Derivative Assets and Liabilities	(223,247)	(7,625)	9,352
Ambac Financial Group, Inc Parent Company Only [Member]
Cash flows from operating activities:
Net income (loss)	(328,715)	74,843	493,403
Adjustments to reconcile net income to net cash used in operating activities:
Amortization of bond premium and discount	(16,724)	(7,208)	(4,690)
Share-based compensation	4,293	5,253	3,105
Current income taxes	(854)	42,126	(71,069)
Investment income due and accrued	(57)	(149)	(69)
Net realized investment gains	6,575	7	27
Other, net	(9,960)	5,814	549
Net cash provided by (used in) operating activities	15,780	77,228	532
Cash flows from investing activities:
Proceeds from matured bonds	186,747	269,459	347,539
Purchases of bonds	(195,853)	(279,582)	(312,419)
Change in short-term investments	(2,961)	(18,491)	(25,143)
Net cash provided by (used in) investing activities	(44,082)	(42,287)	4,724
Cash flows from financing activities:
Proceeds from Warrant Exercises	0	2	3
Payments for Repurchase of Warrants	0	2,717	5,375
Net Cash Provided by (Used in) Financing Activities	0	(2,715)	(5,372)
Cash and Cash Equivalents, Period Increase (Decrease)	(28,302)	32,226	(116)
Cash and cash equivalents at beginning of period	32,251	25	141
Cash and cash equivalents end of period	3,949	32,251	25
Supplemental disclosure of cash flow information
Income Taxes Paid	$ 784	$ 635	$ 394