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, 2017 USD ($)
Future premiums expected to be collected, September 30, 2017	$ 17,154
Future premiums expected to be collected, December 31, 2017	14,693
Future premiums expected to be collected, December 31, 2018	61,748
Future premiums expected to be collected, December 31, 2019	58,367
Future premiums expected to be collected, December 31, 2020	55,492
Future premiums expected to be collected, December 31, 2021	49,222
Future premiums expected to be collected, December 31, 2026	217,611
Future premiums expected to be collected, December 31, 2031	173,390
Future premiums expected to be collected, December 31, 2036	102,072
Future premiums expected to be collected, December 31, 2041	35,463
Future premiums expected to be collected, December 31, 2046	16,977
Future premiums expected to be collected, December 31, 2051	5,250
Future premiums expected to be collected, December 31, 2056	240
Future premiums expected to be collected, Total	807,679
Future expected premiums to be earned, net of reinsurance, September 30, 2017	23,632
Future expected premiums to be earned, net of reinsurance, December 31, 2017	20,366
Future expected premiums to be earned, net of reinsurance, December 31, 2018	72,838
Future expected premiums to be earned, net of reinsurance, December 31, 2019	66,387
Future expected premiums to be earned, net of reinsurance, December 31, 2020	62,269
Future expected premiums to be earned, net of reinsurance, December 31, 2021	57,042
Future expected premiums to be earned, net of reinsurance, December 31, 2026	233,432
Future expected premiums to be earned, net of reinsurance, December 31, 2031	157,907
Future expected premiums to be earned, net of reinsurance, December 31, 2036	88,261
Future expected premiums to be earned, net of reinsurance, December 31, 2041	30,421
Future expected premiums to be earned, net of reinsurance, December 31, 2046	14,596
Future expected premiums to be earned, net of reinsurance, December 31, 2051	6,148
Future expected premiums to be earned, net of reinsurance, December 31, 2056	686
Future expected premiums to be earned, net of reinsurance, Total	$ 833,985