Financial Guarantee Insurance Contracts - Estimated Future Amortization Expense for Insurance Intangible Asset (Detail) - USD ($) $ in Thousands	3 Months Ended								12 Months Ended
	Dec. 31, 2017	Sep. 30, 2017	Jun. 30, 2017	Mar. 31, 2017	Dec. 31, 2016	Sep. 30, 2016	Jun. 30, 2016	Mar. 31, 2016	Dec. 31, 2017	Dec. 31, 2016	Dec. 31, 2015
Insurance Intangible Asset [Member]
Amortization Of Intangible Assets [Line Items]
2018	$ 76,638								$ 76,638
2019	69,082								69,082
2020	63,892								63,892
2021	58,207								58,207
2022	53,908								53,908
Thereafter	525,246								525,246
Successor [Member]
Amortization Of Intangible Assets [Line Items]
Amortization of insurance intangible assets	34,168	$ 45,690	$ 33,471	$ 37,525	$ 40,152	$ 44,553	$ 39,013	$ 50,890	150,854	$ 174,608	$ 169,557
Intangible Assets, Gross (Excluding Goodwill)	1,581,156				1,534,419				1,581,156	1,534,419
Accumulated amortization on insurance intangible asset	$ 734,183				$ 572,339				734,183	572,339
Successor [Member] | Insurance Asset [Member]
Amortization Of Intangible Assets [Line Items]
Amortization of insurance intangible assets									$ 150,854	$ 174,608	$ 169,557