Consolidated Balance Sheets - Successor [Member] - USD ($) $ in Thousands	Jun. 30, 2018	Dec. 31, 2017
Assets:
Fixed income securities, at fair value (amortized cost of $3,355,223 and $4,614,623)	$ 3,514,927	$ 4,652,172
Fixed income securities pledged as collateral, at fair value (amortized cost of $84,641 and $99,719)	84,641	99,719
Short-term investments, at fair value (amortized cost of $393,516 and $557,476)	393,447	557,270
Other investments	394,396	431,630
Total investments	4,387,411	5,740,791
Cash and cash equivalents	44,398	623,703
Receivable for securities	82,513	11,177
Investment income due and accrued	12,157	16,532
Premium receivables	553,958	586,312
Reinsurance recoverable on paid and unpaid losses	39,071	40,997
Deferred ceded premium	47,886	52,195
Subrogation recoverable	1,876,188	631,213
Loans	10,007	10,358
Derivative assets	56,510	73,199
Income Taxes Receivable	34,619	11,803
Insurance intangible asset	786,208	846,973
Other assets	33,631	46,614
Total assets	21,535,223	23,192,374
Liabilities:
Unearned premiums	721,689	783,155
Loss and loss expense reserves	2,057,334	4,745,015
Ceded premiums payable	35,594	37,876
Long-term debt	2,796,389	991,696
Accrued interest payable	237,558	436,984
Derivative Liability	67,648	82,782
Other liabilities	58,191	67,583
Payable for securities purchased	16,556	1,932
Total liabilities	19,471,302	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	208,328	199,560
Accumulated other comprehensive income	45,854	(52,239)
Retained earnings	1,545,702	1,233,845
Treasury stock, shares at cost: 0 and 8,202	(527)	(471)
Total Ambac Financial Group, Inc. stockholders’ equity	1,799,811	1,381,148
Noncontrolling interest	264,110	264,110
Total stockholders’ equity	2,063,921	1,645,258
Total liabilities and stockholders’ equity	21,535,223	23,192,374
Deferred Income Tax Liabilities, Net	32,781	33,659
Variable Interest Entity, Primary Beneficiary [Member]
Assets:
Fixed income securities, at fair value (amortized cost of $3,355,223 and $4,614,623)	2,756,924	2,914,145
Restricted cash	1,052	978
Loans	10,751,199	11,529,384
Derivative assets	60,403	54,877
Other assets	1,088	1,123
Liabilities:
Long-term debt	11,454,746	12,160,544
Accrued interest payable	550	589
Derivative Liability	1,992,227	2,205,264
Other liabilities	$ 39	$ 37