Background and Basis of Presentation - Additional Information (Detail) (USD $) In Thousands, except Share data, unless otherwise specified	9 Months Ended	12 Months Ended
	Sep. 30, 2012	Dec. 31, 2010	Dec. 31, 2011
Background And Basis Of Presentation [Line Items]
Net par exposure for policies allocated to the segregated account	$ 30,450,626
Issuance of secured note to segregated account		2,000,000
Secured note maturity year		2050
Interest on the secured note accrues		4.50%
Available secured notes including capitalized interest	897,248
Minimum surplus amount	100,000
Percentage of permitted policy claim	25.00%
Insurance liabilities allocated to segregated account	6,596,843
Insurance liabilities not assumed under Reinsurance Agreement	296,018
Maximum limit for aggregate face amount of allowed and disputed general unsecured claims	50,000
Amount shall have been paid or paid into escrow by the company	30,000
Current cash and investments	31,459
Restricted cash	$ 2,500		$ 2,500
Ambac [Member]
Background And Basis Of Presentation [Line Items]
Shareholders ownership interest	5.00%
Increase in ownership percentage, by value	50.00%
Increase in ownership percentage, rolling period beginning with the last Ownership Change	Three-year
Beneficially owned shares by the holders	13,500,000
Percentage of stock value of reorganized company	4.50%