Fresh Start Financial Statement Reporting - Schedule of Calculation of Pre-Tax Gain, Recorded as Reorganization on Consolidated Statement of Total Comprehensive Income (Parenthetical) (Detail) (USD $) In Thousands, except Share data, unless otherwise specified	Jun. 30, 2013	Apr. 30, 2013
Extinguishment of Debt [Line Items]
Partial discharge of par value of Segregated Account junior surplus notes		$ 8,043
Enterprise value	185,000	185,000
Common stock, shares issued	45,000,000
Common stock par value	$ 0.01	$ 0.01
Number of warrants issued	5,047,138
Successor Ambac [Member]
Extinguishment of Debt [Line Items]
Common stock	450
Common stock, shares issued	45,002,456	45,000,000
Common stock par value	$ 0.01
Additional paid-in capital	184,565
Number of warrants issued		5,047,138
Common Stock Successor Ambac [Member] | Reorganization Item Adjustments [Member]
Extinguishment of Debt [Line Items]
Common stock		450
Common stock, shares issued		45,000,000
Common stock par value		$ 0.01
Additional Paid-In Capital Successor [Member] | Reorganization Item Adjustments [Member]
Extinguishment of Debt [Line Items]
Additional paid-in capital		184,550
Additional paid-in capital allocated to warrants		11,437
Additional paid-in capital attributable to common stock		$ 173,113