Background and Business Description - Additional Information (Detail)	3 Months Ended	4 Months Ended
	Mar. 31, 2017 USD ($) Segment $ / shares shares	Apr. 30, 2013 shares	Dec. 31, 2016 $ / shares shares	May 01, 2013 $ / shares shares
Background And Basis Of Presentation [Line Items]
Entity Incorporation, Date of Incorporation	Apr. 29, 1991
Number of reportable segments | Segment	2
Investment Warrants Expiration Date		Apr. 30, 2023
Possible Increase in Loss Reserves Related to Puerto Rico	$ 1,600,000,000
Ambac Assurance [Member]
Background And Basis Of Presentation [Line Items]
Net par exposure for policies allocated to the Segregated Account	11,274,275,000
Minimum surplus amount	$ 100,000,000
Successor [Member]
Background And Basis Of Presentation [Line Items]
Common stock, shares authorized | shares	130,000,000		130,000,000
Common Stock, Par or Stated Value Per Share | $ / shares	$ 0.01		$ 0.01	$ 0.01
Preferred stock, shares authorized | shares	20,000,000		20,000,000
Preferred Stock, Par or Stated Value Per Share | $ / shares	$ 0.01		$ 0.01
Common stock, shares issued | shares	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	$ 169,400,000
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
Change in Loss Assumptions	(18,300,000)
Net Impact of Change in Reserves Related to Ballantyne Settlement	73,300,000
Previous Benefit Through Reduction of Loss and LAE	53,000,000
Total Benefit Related to Ballantyne Settlement	$ 144,600,000