Financial Guarantee Insurance Contracts - Summarized Future Gross Undiscounted Premiums Expected to be Collected, and Future Expected Premiums Earned, Net of Reinsurance (Detail) (USD $) In Thousands, unless otherwise specified	Jun. 30, 2013
Insurance [Abstract]
Future premiums expected to be collected, September 30, 2013	$ 30,861
Future premiums expected to be collected, December 31, 2013	30,424
Future premiums expected to be collected, December 31, 2014	123,642
Future premiums expected to be collected, December 31, 2015	123,327
Future premiums expected to be collected, December 31, 2016	117,119
Future premiums expected to be collected, December 31, 2017	111,175
Future premiums expected to be collected, December 31, 2022	492,046
Future premiums expected to be collected, December 31, 2027	388,834
Future premiums expected to be collected, December 31, 2032	278,704
Future premiums expected to be collected, December 31, 2037	147,485
Future premiums expected to be collected, December 31, 2042	50,568
Future premiums expected to be collected, December 31, 2047	15,500
Future premiums expected to be collected, December 31, 2052	3,639
Future premiums expected to be collected, December 31, 2057	92
Future premiums expected to be collected, Total	1,913,416
Future expected premiums to be earned, net of reinsurance, September 30, 2013	54,293
Future expected premiums to be earned, net of reinsurance, December 31, 2013	51,219
Future expected premiums to be earned, net of reinsurance, December 31, 2014	186,861
Future expected premiums to be earned, net of reinsurance, December 31, 2015	168,317
Future expected premiums to be earned, net of reinsurance, December 31, 2016	155,390
Future expected premiums to be earned, net of reinsurance, December 31, 2017	144,456
Future expected premiums to be earned, net of reinsurance, December 31, 2022	595,171
Future expected premiums to be earned, net of reinsurance, December 31, 2027	415,115
Future expected premiums to be earned, net of reinsurance, December 31, 2032	257,389
Future expected premiums to be earned, net of reinsurance, December 31, 2037	124,197
Future expected premiums to be earned, net of reinsurance, December 31, 2042	41,733
Future expected premiums to be earned, net of reinsurance, December 31, 2047	14,512
Future expected premiums to be earned, net of reinsurance, December 31, 2052	4,692
Future expected premiums to be earned, net of reinsurance, December 31, 2057	297
Future expected premiums to be earned, net of reinsurance, Total	$ 2,213,642