Financial Guarantees in Force - Additional Information (Detail) - USD ($) $ in Thousands	12 Months Ended
	Dec. 31, 2015	Dec. 31, 2014
Guarantor Obligations [Line Items]
Gross par amount of financial guarantees outstanding	$ 119,235,000	$ 159,688,000
Net par amount of financial guarantees	108,299,000	144,734,000
Gross financial guarantees in force	188,853,000	253,383,000
Net financial guarantees in force	$ 171,000,000	$ 228,890,000
Highest single insured risk of aggregate net par amount guaranteed	1.60%
California [Member]
Guarantor Obligations [Line Items]
Aggregate net par amounts in force	14.30%
New York [Member]
Guarantor Obligations [Line Items]
Aggregate net par amounts in force	5.30%
No other state [Member] | Maximum [Member]
Guarantor Obligations [Line Items]
Aggregate net par amounts in force	5.00%