Financial Guarantee Insurance Contracts - Summarized Future Gross Undiscounted Premiums Expected to be Collected, and Future Expected Premiums Earned, Net of Reinsurance (Detail) - Successor [Member] $ in Thousands	Jun. 30, 2018 USD ($)
Future premiums expected to be collected, September 30, 2018	$ 14,870
Future premiums expected to be collected, December 31, 2018	11,906
Future premiums expected to be collected, December 31, 2019	53,357
Future premiums expected to be collected, December 31, 2020	50,663
Future premiums expected to be collected, December 31, 2021	44,623
Future premiums expected to be collected, December 31, 2022	42,702
Future premiums expected to be collected, December 31, 2027	190,365
Future premiums expected to be collected, December 31, 2032	149,700
Future premiums expected to be collected, December 31, 2037	84,272
Future premiums expected to be collected, December 31, 2042	30,773
Future premiums expected to be collected, December 31, 2047	14,357
Future premiums expected to be collected, December 31, 2052	3,621
Future premiums expected to be collected, December 31, 2057	95
Future premiums expected to be collected, Total	691,304
Future expected premiums to be earned, net of reinsurance, September 30, 2018	15,557
Future expected premiums to be earned, net of reinsurance, December 31, 2018	15,396
Future expected premiums to be earned, net of reinsurance, December 31, 2019	58,623
Future expected premiums to be earned, net of reinsurance, December 31, 2020	54,829
Future expected premiums to be earned, net of reinsurance, December 31, 2021	50,054
Future expected premiums to be earned, net of reinsurance, December 31, 2022	46,732
Future expected premiums to be earned, net of reinsurance, December 31, 2027	190,800
Future expected premiums to be earned, net of reinsurance, December 31, 2032	128,304
Future expected premiums to be earned, net of reinsurance, December 31, 2037	71,289
Future expected premiums to be earned, net of reinsurance, December 31, 2042	24,543
Future expected premiums to be earned, net of reinsurance, December 31, 2047	12,732
Future expected premiums to be earned, net of reinsurance, December 31, 2052	4,647
Future expected premiums to be earned, net of reinsurance, December 31, 2057	297
Future expected premiums to be earned, net of reinsurance, Total	$ 673,803