Financial Guarantee Insurance Contracts - Summarized Future Gross Undiscounted Premiums Expected to be Collected, and Future Expected Premiums Earned, Net of Reinsurance (Detail) $ in Thousands	Jun. 30, 2016 USD ($)
Insurance [Abstract]
Future premiums expected to be collected, September 30, 2015	$ 21,184
Future premiums expected to be collected, December 31, 2015	17,936
Future premiums expected to be collected, December 31, 2016	69,067
Future premiums expected to be collected, December 31, 2017	64,564
Future premiums expected to be collected, December 31, 2018	60,977
Future premiums expected to be collected, December 31, 2019	57,954
Future premiums expected to be collected, December 31, 2024	237,920
Future premiums expected to be collected, December 31, 2029	193,274
Future premiums expected to be collected, December 31, 2034	126,150
Future premiums expected to be collected, December 31, 2039	43,602
Future premiums expected to be collected, December 31, 2044	20,112
Future premiums expected to be collected, December 31, 2049	7,238
Future premiums expected to be collected, December 31, 2054	601
Future premiums expected to be collected, Total	920,579
Future expected premiums to be earned, net of reinsurance, September 30, 2015	30,477
Future expected premiums to be earned, net of reinsurance, December 31, 2015	28,639
Future expected premiums to be earned, net of reinsurance, December 31, 2016	94,811
Future expected premiums to be earned, net of reinsurance, December 31, 2017	80,752
Future expected premiums to be earned, net of reinsurance, December 31, 2018	74,629
Future expected premiums to be earned, net of reinsurance, December 31, 2019	70,147
Future expected premiums to be earned, net of reinsurance, December 31, 2024	282,657
Future expected premiums to be earned, net of reinsurance, December 31, 2029	195,912
Future expected premiums to be earned, net of reinsurance, December 31, 2034	114,686
Future expected premiums to be earned, net of reinsurance, December 31, 2039	41,486
Future expected premiums to be earned, net of reinsurance, December 31, 2044	17,600
Future expected premiums to be earned, net of reinsurance, December 31, 2049	7,796
Future expected premiums to be earned, net of reinsurance, December 31, 2054	1,299
Future expected premiums to be earned, net of reinsurance, Total	$ 1,040,891