Financial Guarantee Insurance - Summary of Percentage Ceded to Reinsurers and Reinsurance Recoverable and Rating Levels (Detail) (USD $) In Thousands, unless otherwise specified	12 Months Ended
	Dec. 31, 2014
Summary of Ceded Par and Net Unsecured Reinsurance Recoverable [Line Items]
Percentage ceded Par	100.00%
Net unsecured reinsurance recoverable	$ 41,941
Assured Guaranty Re Ltd [Member] | Negative [Member] | Moody's, Baa1 Rating [Member]
Summary of Ceded Par and Net Unsecured Reinsurance Recoverable [Line Items]
Percentage ceded Par	89.40%
Net unsecured reinsurance recoverable	37,553
Sompo Japan Nipponkoa Holdings, Inc [Member] | Stable [Member] | Moody's, A1 Rating [Member]
Summary of Ceded Par and Net Unsecured Reinsurance Recoverable [Line Items]
Percentage ceded Par	6.10%
Net unsecured reinsurance recoverable	0
Assured Guaranty Corporation [Member] | Negative [Member] | Moody's, A3 Rating [Member]
Summary of Ceded Par and Net Unsecured Reinsurance Recoverable [Line Items]
Percentage ceded Par	4.50%
Net unsecured reinsurance recoverable	$ 4,388