Background and Business Description - Additional Information (Detail)	3 Months Ended			4 Months Ended	6 Months Ended
	Jun. 30, 2017 USD ($) $ / shares shares	Mar. 31, 2017 USD ($)	Jun. 30, 2016 USD ($)	Apr. 30, 2013 shares	Jun. 30, 2017 USD ($) $ / shares shares	Jun. 30, 2016 USD ($)	Dec. 31, 2016 USD ($) $ / shares shares	May 01, 2013 $ / shares shares
Background And Basis Of Presentation [Line Items]
Gain (Loss) on Sale of Derivatives	$ 43,443,000				$ 42,157,000
Financial Guarantee Insurance Contracts, Accelerated Premium Revenue, Amount	2,600,000
Entity Incorporation, Date of Incorporation					Apr. 29, 1991
Investment Warrants Expiration Date				Apr. 30, 2023
Possible Increase in Loss Reserves Related to Puerto Rico					$ 0
Payments for Derivative Instrument, Financing Activities					103,592,000
Ambac Assurance [Member]
Background And Basis Of Presentation [Line Items]
Net par exposure for policies allocated to the Segregated Account	10,772,572,000				10,772,572,000
Minimum surplus amount	100,000,000				100,000,000
Successor [Member]
Background And Basis Of Presentation [Line Items]
Gain (Loss) on Sale of Derivatives	1,134,000		$ 233,000		1,333,000	$ 485,000
Financial Guarantee Insurance Contracts, Accelerated Premium Revenue, Amount	$ 13,190,000		$ 5,081,000		$ 29,470,000	$ 20,057,000
Number of Reportable Segments		2
Common stock, shares authorized | shares	130,000,000				130,000,000		130,000,000
Common Stock, Par or Stated Value Per Share | $ / shares	$ 0.01				$ 0.01		$ 0.01	$ 0.01
Preferred stock, shares authorized | shares	20,000,000				20,000,000		20,000,000
Preferred Stock, Par or Stated Value Per Share | $ / shares	$ 0.01				$ 0.01		$ 0.01
Common stock, shares issued | shares	45,275,982				45,275,982		45,194,954	45,000,000
Warrants Distributed In Bankruptcy | shares				5,047,138				5,047,138
Warrants issued exercise price | $ / shares								$ 16.67
Puerto Rico Losses in Public Finance Sector					$ 221,604,000
Derivative Liability	$ 91,549,000				91,549,000		$ 319,286,000
Successor [Member] | Ambac UK [Member]
Background And Basis Of Presentation [Line Items]
Ballantyne Settlement with JPMIM					325,600,000
Ambac UK Benefit Through Loss Reduction					91,600,000
Previous Benefit Through Reduction of Loss and LAE					53,000,000
Total Benefit Related to Ballantyne Settlement					144,600,000
Derivative Liability Termination Payment [Domain]
Background And Basis Of Presentation [Line Items]
Payments for Derivative Instrument, Financing Activities					$ 94,407,000
Derivative Financial Instruments, Liabilities [Member]
Background And Basis Of Presentation [Line Items]
Derivative Liability		$ 147,035,000