Financial Guarantee Insurance Contracts - Summary of Loss Reserve Roll-Forward, Net of Subrogation Recoverable and Reinsurance (Detail) € in Thousands, $ in Thousands	6 Months Ended
	Jun. 30, 2018 USD ($)	Jun. 30, 2018 EUR (€)	Jun. 30, 2017 USD ($)	Jun. 30, 2017 EUR (€)	Jun. 30, 2018 USD ($)	Feb. 12, 2018 USD ($)	Dec. 31, 2017 USD ($)	Jun. 30, 2017 USD ($)
Successor [Member]
Liability for Unpaid Claims and Claims Adjustment Expense [Roll Forward]
Beginning gross loss and loss expense reserves	$ 4,113,802		$ 3,696,038
Less reinsurance on loss and loss expense reserves	40,658		30,767
Beginning balance of net loss and loss expense reserves	4,073,144		3,665,271
Current Year Claims and Claims Adjustment Expense	996		5,137
Prior Year Claims and Claims Adjustment Expense	(215,812)		195,974
Liability for Unpaid Claims and Claims Adjustment Expense, Incurred Claims	(214,816)		201,111
Claim and loss expense payments, net of subrogation and reinsurance	(105)		(153)
Claim and loss expense (payments) recoveries, net of subrogation and reinsurance	(3,708,992)		(7,607)
Liability for Unpaid Claims and Claims Adjustment Expense, Claims Paid	3,709,097		7,760
Liability for Unpaid Claims and Claims Adjustment Expense, Foreign Currency Translation Gain (Loss)	(6,378)		17,622
Liability for Unpaid Claims and Claims Adjustment Expense, Net	4,073,144		3,665,271		$ 142,853		$ 4,073,144	$ 3,876,244
Add reinsurance on loss and loss expense reserves	38,293		47,034
Ending gross loss and loss expense reserves	181,146		3,923,278
Policyholder Benefits and Claims Incurred, Ceded	(870)		16,469
Net Incurred RMBS Subrogation Recoveries	(17,602)		(22,175)
SatisfactionAndDischargeOfSegregatedAccountDeferredPrincipalAmounts						$ 3,000,158
SatisfactionAndDischargeOfSegregatedAccountDeferredInterestAmounts						856,834
Loss and Loss Expense Benefit on Settled Deferred Amounts						$ 288,204
Ceded Loss And Loss Expenses Paid Not Yet Recovered					$ 778		$ 339	$ (568)
Euro Member Countries, Euro
Liability for Unpaid Claims and Claims Adjustment Expense [Roll Forward]
Ending gross loss and loss expense reserves	$ 15,084	€ 12,927	$ 20,212	€ 17,699