Schedule II - Condensed Financial Information of Registrant (Parent Company Only) - Condensed Balance Sheet (Detail) - USD ($) $ in Thousands	Dec. 31, 2016	Dec. 31, 2015	Dec. 31, 2014	May 01, 2013
Condensed Balance Sheet Statements, Captions [Line Items]
Tolling Payment Payable to AFG	$ 28,691	$ 70,911
Assets:
Junior surplus note of Ambac Assurance Segregated Account				$ 350,000
Successor [Member]
Assets:
Fixed income securities, at fair value	5,554,215	5,043,776
Other investments	450,307	310,600
Total investments	6,500,215	5,644,720
Investment income due and accrued	26,023	25,264
Other assets	158,423	185,877
Total assets	22,635,702	23,728,070	$ 25,159,864
Liabilities:
Current taxes	14,280	5,835
Total liabilities	20,657,678	21,769,724
Stockholders' equity (deficit):
Preferred stock	0	0
Common stock	452	450
Additional paid-in capital	195,267	190,813
Accumulated other comprehensive income (loss)	(38,990)	15,215	$ 220,283
Retained earnings	1,557,681	1,478,439
Common stock held in treasury at cost	(496)	(118)
Total Ambac Financial Group, Inc. stockholders’ equity	1,713,914	1,684,799
Total liabilities and stockholders’ equity	22,635,702	23,728,070
Ambac Financial Group, Inc Parent Company Only [Member] | Successor [Member]
Assets:
Fixed income securities, at fair value	214,023	187,979
Short-term investments, at cost (approximates fair value)	66,570	48,079
Other investments	30,003	25,339
Total investments	310,596	261,397
Cash	32,251	25
Investment in subsidiaries	1,340,442	1,349,483
Investment income due and accrued	272	123
Current taxes receivable	28,722	70,848
Other assets	4,132	4,778
Total assets	1,716,415	1,686,654
Liabilities:
Accounts payable and other liabilities	2,501	1,855
Total liabilities	2,501	1,855
Stockholders' equity (deficit):
Preferred stock	0	0
Common stock	452	450
Additional paid-in capital	195,267	190,813
Accumulated other comprehensive income (loss)	(38,990)	15,215
Retained earnings	1,557,681	1,478,439
Common stock held in treasury at cost	(496)	(118)
Total Ambac Financial Group, Inc. stockholders’ equity	1,713,914	1,684,799
Total liabilities and stockholders’ equity	$ 1,716,415	$ 1,686,654