Background and Business Description - Additional Information (Detail)			1 Months Ended	4 Months Ended	12 Months Ended
	Dec. 22, 2014	Jun. 11, 2014	Apr. 30, 2013 USD ($) $ / shares shares	Apr. 30, 2013 $ / shares shares	Dec. 31, 2016 USD ($) Segment $ / shares shares	Dec. 31, 2015 USD ($) $ / shares shares	Dec. 31, 2014 USD ($) Rate	Dec. 31, 2010 USD ($)	May 01, 2013 USD ($) $ / shares shares
Background And Basis Of Presentation [Line Items]
Unpaid as a Percentage of Permitted Policy Claims | Rate							55.00%
Entity Incorporation, Date of Incorporation					Apr. 29, 1991
Number of reportable segments | Segment					2
Par Value of Private Placement							$ 299,175,000
Private Placement Par Value Proceeds							80.00%
Private Placement Maturity Date							Aug. 28, 2039
Interest on junior surplus notes							5.10%
Investment Warrants Expiration Date				Apr. 30, 2023
Transaction Limit					$ 5,000,000
Accrued rate of interest on outstanding policy obligations (percent)		5.10%			5.10%		5.10%
Payment of permitted policy claim (percent)	25.00%						25.00%
Equalizing payment on unpaid permitted policy claim (percent)							26.67%
December 2014 Payment of Deferred Amounts							$ 1,137,202,000
Capital Stock Authorized | shares			150,000,000	150,000,000
Common stock, shares authorized | shares			130,000,000	130,000,000
Common Stock, Par or Stated Value Per Share | $ / shares			$ 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			45,000,000	45,000,000
Warrants issued exercise price | $ / shares			$ 16.67	$ 16.67
Junior surplus note of Ambac Assurance Segregated Account									$ 350,000,000
Common Stock Voting Restrictions							10.00%
Common Stock Voting Restriction Less One Vote							10.00%
Common Stock Transfer Restrictions							5.00%
Common Stock Additional Transfer Restrictions							5.00%
November 2014 Payment of Surplus Notes							$ 413,587,000
Litigation Settlement, Amount					$ 995,000,000
Ambac Assurance [Member]
Background And Basis Of Presentation [Line Items]
Net par exposure for policies allocated to the Segregated Account					11,884,751,000
Issuance of secured note to segregated account								$ 2,000,000,000
Secured note maturity year								2050
Interest on the secured note accrues								4.50%
Minimum surplus amount					100,000,000
Maximum Reimbursement Of Operating Expenses			$ 5,000,000
Successor [Member]
Background And Basis Of Presentation [Line Items]
Proceeds from the sale of Junior Surplus Notes of the Segregated Account					$ 0	$ 0	$ 224,262,000
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					45,194,954	45,044,222			45,000,000
Warrants Distributed In Bankruptcy | shares			5,047,138	5,047,138					5,047,138
Warrants issued exercise price | $ / shares									$ 16.67
Two Thousand And Seventeen [Member] | Ambac Assurance [Member]
Background And Basis Of Presentation [Line Items]
Maximum Reimbursement Of Operating Expenses after 2017			$ 4,000,000