Financial Guarantee Insurance Contracts - Summarized Future Gross Undiscounted Premiums Expected to be Collected, and Future Expected Premiums Earned, Net of Reinsurance (Detail) $ in Thousands	Mar. 31, 2016 USD ($)
Insurance [Abstract]
Future premiums expected to be collected, June 30. 2015	$ 19,259
Future premiums expected to be collected, September 30, 2015	18,942
Future premiums expected to be collected, December 31, 2015	19,299
Future premiums expected to be collected, December 31, 2016	72,081
Future premiums expected to be collected, December 31, 2017	67,527
Future premiums expected to be collected, December 31, 2018	63,878
Future premiums expected to be collected, December 31, 2019	60,815
Future premiums expected to be collected, December 31, 2024	249,945
Future premiums expected to be collected, December 31, 2029	203,751
Future premiums expected to be collected, December 31, 2034	131,456
Future premiums expected to be collected, December 31, 2039	44,366
Future premiums expected to be collected, December 31, 2044	20,266
Future premiums expected to be collected, December 31, 2049	7,247
Future premiums expected to be collected, December 31, 2054	601
Future premiums expected to be collected, Total	979,433
Future expected premiums to be earned, net of reinsurance, June 30, 2015	31,587
Future expected premiums to be earned, net of reinsurance, September 30, 2015	29,248
Future expected premiums to be earned, net of reinsurance, December 31, 2015	27,519
Future expected premiums to be earned, net of reinsurance, December 31, 2016	96,126
Future expected premiums to be earned, net of reinsurance, December 31, 2017	84,162
Future expected premiums to be earned, net of reinsurance, December 31, 2018	77,934
Future expected premiums to be earned, net of reinsurance, December 31, 2019	73,366
Future expected premiums to be earned, net of reinsurance, December 31, 2024	294,692
Future expected premiums to be earned, net of reinsurance, December 31, 2029	203,435
Future expected premiums to be earned, net of reinsurance, December 31, 2034	119,037
Future expected premiums to be earned, net of reinsurance, December 31, 2039	42,309
Future expected premiums to be earned, net of reinsurance, December 31, 2044	17,763
Future expected premiums to be earned, net of reinsurance, December 31, 2049	7,818
Future expected premiums to be earned, net of reinsurance, December 31, 2054	1,298
Future expected premiums to be earned, net of reinsurance, Total	$ 1,106,294