Consolidated Balance Sheets - Successor [Member] - USD ($) $ in Thousands	Mar. 31, 2018	Dec. 31, 2017
Assets:
Fixed income securities, at fair value (amortized cost of $3,713,908 and $4,614,623)	$ 3,871,938	$ 4,652,172
Fixed income securities pledged as collateral, at fair value (amortized cost of $84,240 and $99,719)	84,240	99,719
Short-term investments, at fair value (amortized cost of $321,210 and $557,476)	321,119	557,270
Other investments	419,896	431,630
Total investments	4,697,193	5,740,791
Cash and cash equivalents	38,485	623,703
Receivable for securities	2,376	11,177
Investment income due and accrued	20,457	16,532
Premium receivables	580,707	586,312
Reinsurance recoverable on paid and unpaid losses	38,825	40,997
Deferred ceded premium	49,631	52,195
Subrogation recoverable	1,894,778	631,213
Loans	10,643	10,358
Derivative assets	60,196	73,199
Income Taxes Receivable	20,180	11,803
Insurance intangible asset	833,040	846,973
Other assets	36,332	46,614
Total assets	22,847,966	23,192,374
Liabilities:
Unearned premiums	762,240	783,155
Loss and loss expense reserves	2,139,101	4,745,015
Ceded premiums payable	36,451	37,876
Long-term debt	2,957,732	991,696
Accrued interest payable	244,199	436,984
Derivative Liability	71,584	82,782
Other liabilities	55,209	67,583
Payable for securities purchased	8,849	1,932
Total liabilities	20,738,801	21,547,116
Stockholders’ equity:
Preferred stock, par value $0.01 per share; 20,000,000 shares authorized; issued and outstanding shares—none	0	0
Common Stock, Value, Issued	454	453
Additional paid-in capital	204,172	199,560
Accumulated other comprehensive income	99,476	(52,239)
Retained earnings	1,541,464	1,233,845
Treasury stock, shares at cost: 0 and 8,202	(511)	(471)
Total Ambac Financial Group, Inc. stockholders’ equity	1,845,055	1,381,148
Noncontrolling interest	264,110	264,110
Total stockholders’ equity	2,109,165	1,645,258
Total liabilities and stockholders’ equity	22,847,966	23,192,374
Deferred Income Tax Liabilities, Net	34,804	33,659
Variable Interest Entity, Primary Beneficiary [Member]
Assets:
Fixed income securities, at fair value (amortized cost of $3,713,908 and $4,614,623)	2,955,763	2,914,145
Restricted cash	1,134	978
Loans	11,558,331	11,529,384
Derivative assets	46,260	54,877
Other assets	3,635	1,123
Liabilities:
Long-term debt	12,270,124	12,160,544
Accrued interest payable	3,005	589
Derivative Liability	2,155,456	2,205,264
Other liabilities	$ 47	$ 37