Consolidated Balance Sheets - Successor [Member] - USD ($) $ in Thousands	Dec. 31, 2017	Dec. 31, 2016
Assets:
Fixed income securities, at fair value	$ 4,652,172	$ 5,554,215
Fixed income securities pledged as collateral, at fair value	99,719	64,905
Short-term investments, at fair value	557,270	430,788
Other Investments	431,630	450,307
Total investments	5,740,791	6,500,215
Cash and cash equivalents	623,703	91,025
Receivable for securities	11,177	2,090
Investment income due and accrued	16,532	26,023
Premium receivables	586,312	661,337
Reinsurance recoverable on paid and unpaid losses	40,997	30,418
Deferred ceded premium	52,195	69,624
Subrogation recoverable	631,213	684,731
Loans	10,358	4,160
Derivative assets	73,199	77,742
Income Taxes Receivable, Current	11,803	0
Insurance intangible asset	846,973	962,080
Other assets	46,614	158,423
Total assets	23,192,374	22,635,702
Liabilities:
Unearned premiums	783,155	967,258
Loss and loss expense reserves	4,745,015	4,380,769
Ceded premiums payable	37,876	42,529
Obligations under investment agreements	0	82,358
Deferred Income Tax Liabilities, Net	33,659	1,720
Current taxes	0	14,280
Long-term debt	991,696	1,114,405
Accrued interest payable	436,984	421,975
Derivative liabilities	82,782	319,286
Other liabilities	67,583	76,589
Payable for securities purchased	1,932	1,084
Variable interest entity liabilities:
Total liabilities	21,547,116	20,657,678
Stockholders’ equity:
Preferred stock, par value $0.01 per share; 20,000,000 shares authorized shares; issued and outstanding shares—none	0	0
Common stock, par value $0.01 per share; 130,000,000 shares authorized; issued and outstanding shares: 45,275,982 and 45,194,954	453	452
Additional paid-in capital	199,560	195,267
Accumulated other comprehensive income (loss)	(52,239)	(38,990)
Retained earnings	1,233,845	1,557,681
Treasury stock, shares at cost: 24,816 and 22,458	(471)	(496)
Total Ambac Financial Group, Inc. stockholders’ equity	1,381,148	1,713,914
Noncontrolling interest	264,110	264,110
Total stockholders’ equity	1,645,258	1,978,024
Total liabilities and stockholders’ equity	23,192,374	22,635,702
Variable Interest Entity [Member]
Assets:
Fixed income securities, at fair value	2,914,145	2,622,566
Derivative assets	54,877	80,407
Other assets	1,123	1,025
Variable interest entity assets:
Restricted cash	978	4,873
Loans, at fair value	11,529,384	10,658,963
Liabilities:
Long-term debt	12,160,544	11,155,936
Accrued interest payable	589	859
Derivative liabilities	2,205,264	2,078,601
Other liabilities	$ 37	$ 29