Background and Business Description - Additional Information (Detail) - USD ($) $ / shares in Units, $ in Thousands	3 Months Ended		4 Months Ended	12 Months Ended
	Mar. 31, 2018	Mar. 31, 2017	Apr. 30, 2013	Dec. 31, 2017	May 01, 2013
Background And Basis Of Presentation [Line Items]
Entity Incorporation, Date of Incorporation	Apr. 29, 1991
Investment Warrants Expiration Date			Apr. 30, 2023
Successor [Member]
Background And Basis Of Presentation [Line Items]
Other investments	$ 419,896			$ 431,630
Gain (Loss) on Sale of Derivatives	106	$ 199
Financial Guarantee Insurance Contracts, Accelerated Premium Revenue, Amount	$ 9,392	$ 16,280
Common stock, shares authorized	130,000,000			130,000,000
Common Stock, Par or Stated Value Per Share	$ 0.01			$ 0.01	$ 0.01
Preferred stock, shares authorized	20,000,000			20,000,000
Preferred Stock, Par or Stated Value Per Share	$ 0.01			$ 0.01
Common stock, shares issued					45,000,000
Warrants Distributed In Bankruptcy			5,047,138		5,047,138
Warrants issued exercise price					$ 16.67
Derivative Liability	$ 71,584			$ 82,782
Successor [Member] | Ambac UK [Member]
Background And Basis Of Presentation [Line Items]
Ambac UK Benefit Through Loss Reduction				$ 91,600