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	Mar. 31, 2018 USD ($)
Future premiums expected to be collected, June 30. 2018	$ 14,957
Future premiums expected to be collected, September 30, 2018	14,771
Future premiums expected to be collected, December 31, 2018	12,947
Future premiums expected to be collected, December 31, 2019	55,142
Future premiums expected to be collected, December 31, 2020	52,344
Future premiums expected to be collected, December 31, 2021	45,913
Future premiums expected to be collected, December 31, 2022	43,923
Future premiums expected to be collected, December 31, 2027	195,614
Future premiums expected to be collected, December 31, 2032	153,584
Future premiums expected to be collected, December 31, 2037	85,689
Future premiums expected to be collected, December 31, 2042	31,028
Future premiums expected to be collected, December 31, 2047	14,425
Future premiums expected to be collected, December 31, 2052	3,620
Future premiums expected to be collected, December 31, 2057	92
Future premiums expected to be collected, Total	724,049
Future expected premiums to be earned, net of reinsurance, June 30, 2018	17,037
Future expected premiums to be earned, net of reinsurance, September 30, 2018	16,388
Future expected premiums to be earned, net of reinsurance, December 31, 2018	15,946
Future expected premiums to be earned, net of reinsurance, December 31, 2019	60,697
Future expected premiums to be earned, net of reinsurance, December 31, 2020	56,759
Future expected premiums to be earned, net of reinsurance, December 31, 2021	51,792
Future expected premiums to be earned, net of reinsurance, December 31, 2022	48,292
Future expected premiums to be earned, net of reinsurance, December 31, 2027	196,972
Future expected premiums to be earned, net of reinsurance, December 31, 2032	132,598
Future expected premiums to be earned, net of reinsurance, December 31, 2037	73,307
Future expected premiums to be earned, net of reinsurance, December 31, 2042	25,070
Future expected premiums to be earned, net of reinsurance, December 31, 2047	12,798
Future expected premiums to be earned, net of reinsurance, December 31, 2052	4,656
Future expected premiums to be earned, net of reinsurance, December 31, 2057	297
Future expected premiums to be earned, net of reinsurance, Total	$ 712,609