Fresh Start Financial Statement Reporting - Schedule of Calculation of Pre-Tax Gain, Recorded as Reorganization on Consolidated Statement of Total Comprehensive Income (Detail) $ in Thousands	Apr. 30, 2013 USD ($)
Extinguishment of Debt [Line Items]
Liabilities subject to compromise	$ (1,704,641)
Long-term debt	973
Accrued interest payable	821
Total debt discharged	1,706,435
Less: Successor Ambac common stock	(450)
Successor Ambac additional paid-in capital	(184,550)
Pre-tax gain from cancellation and satisfaction of Predecessor Ambac debt	1,521,435
Predecessor [Member]
Extinguishment of Debt [Line Items]
Liabilities subject to compromise	(1,704,641)
Predecessor [Member] \| Common Stock Successor Ambac [Member]
Extinguishment of Debt [Line Items]
Less: Successor Ambac common stock	0
Predecessor [Member] \| Additional Paid-In Capital Successor [Member]
Extinguishment of Debt [Line Items]
Successor Ambac additional paid-in capital	$ 0

Excess of issue price over par or stated value of the entity's capital stock and amounts received from other transactions involving the entity's stock or stockholders. Includes adjustments to additional paid in capital. Some examples of such adjustments include recording the issuance of debt with a beneficial conversion feature and certain tax consequences of equity instruments awarded to employees. Use this element for the aggregate amount of additional paid-in capital associated with common and preferred stock. For additional paid-in capital associated with only common stock, use the element additional paid in capital, common stock. For additional paid-in capital associated with only preferred stock, use the element additional paid in capital, preferred stock.

Reference 1: http://www.xbrl.org/2003/role/presentationRef
-Publisher FASB
-Name Accounting Standards Codification
-Topic 210
-SubTopic 10
-Section S99
-Paragraph 1
-Subparagraph (SX 210.5-02.30(a)(1))
-URI http://asc.fasb.org/extlink&oid=6877327&loc=d3e13212-122682

Reference 2: http://www.xbrl.org/2003/role/presentationRef
-Publisher SEC
-Name Regulation S-X (SX)
-Number 210
-Section 02
-Paragraph 31
-Article 5

Name:	us-gaap_AdditionalPaidInCapital
Namespace Prefix:	us-gaap_
Data Type:	xbrli:monetaryItemType
Balance Type:	credit
Period Type:	instant