Background and Business Description - Additional Information (Detail) (USD $)	3 Months Ended	9 Months Ended	12 Months Ended
	Sep. 30, 2014	Sep. 30, 2014 Rate	Dec. 31, 2010 Ambac Assurance [Member]	Sep. 30, 2014 Ambac Assurance [Member]	Sep. 30, 2014 Ambac Assurance [Member] Minimum [Member]
Background And Basis Of Presentation [Line Items]
Debt Instrument, Face Amount	$ 350,000,000	$ 350,000,000
Proceeds From The Sale Of Junior Surplus Notes	224,262,000
Par Value of Owner Trust Certificate	74,794,000	74,794,000
Par Value of Private Placement	299,175,000	299,175,000
Percentage of Junior Surplus Notes		80.00%
Rate on Private Placement Obligations		5.10%
Net par exposure for policies allocated to the Segregated Account				19,650,823,000
Issuance of secured note to segregated account			2,000,000,000
Secured note maturity year			2050
Interest on the secured note accrues			4.50%
Available secured notes including capitalized interest				0
Minimum surplus amount					100,000,000
Policyholders surplus				$ 897,692,000
Accrued rate of interest on outstanding policy obligations (percent)		5.10%
Payment of permitted policy claim (percent)		25.00%
Future payment of permitted policy claim (percent)		45.00%
Future unpaid permitted policy claims (percent)		55.00%
Equalizing payment on unpaid permitted policy claim (percent)		26.67%