Comprehensive Income - Schedule of Changes in Balances of Each Component of Accumulated Other Comprehensive Income (Detail) (USD $) In Thousands, unless otherwise specified	2 Months Ended	1 Months Ended	4 Months Ended	2 Months Ended	1 Months Ended	4 Months Ended	2 Months Ended	1 Months Ended	4 Months Ended	2 Months Ended	1 Months Ended	4 Months Ended
Jun. 30, 2013 Successor Ambac [Member]	Apr. 30, 2013 Predecessor Ambac [Member]	Apr. 30, 2013 Predecessor Ambac [Member]	Jun. 30, 2013 Unrealized Gains (Losses) on Available-for-Sale Securities [Member] Successor Ambac [Member]	Apr. 30, 2013 Unrealized Gains (Losses) on Available-for-Sale Securities [Member] Predecessor Ambac [Member]	Apr. 30, 2013 Unrealized Gains (Losses) on Available-for-Sale Securities [Member] Predecessor Ambac [Member]	Jun. 30, 2013 Amortization of Postretirement Benefit [Member] Successor Ambac [Member]	Apr. 30, 2013 Amortization of Postretirement Benefit [Member] Predecessor Ambac [Member]	Apr. 30, 2013 Amortization of Postretirement Benefit [Member] Predecessor Ambac [Member]	Jun. 30, 2013 Gain (Loss) on Foreign Currency Translation [Member] Successor Ambac [Member]	Apr. 30, 2013 Gain (Loss) on Foreign Currency Translation [Member] Predecessor Ambac [Member]	Apr. 30, 2013 Gain (Loss) on Foreign Currency Translation [Member] Predecessor Ambac [Member]
Accumulated Other Comprehensive Income Loss Net Of Tax [Line Items]
Beginning Balance		$ 720,071	$ 625,385		$ 745,370	$ 651,272		$ (5,052)	$ (5,860)		$ (20,247)	$ (20,027)
Other comprehensive income before reclassifications	(85,035)	88,079	188,039	(72,511)	88,516	188,696				(12,524)	(437)	(657)
Amounts reclassified from accumulated other comprehensive income	(18,472)	(7,890)	(13,164)	(18,472)	(7,267)	(13,349)		(623)	185
Elimination of Predecessor Ambac Shareholder Equity Accounts		(800,260)	(800,260)		(826,619)	(826,619)		5,675	5,675		20,684	20,684
Net current period other comprehensive income	(103,507)	(720,071)	(625,385)	(90,983)	(745,370)	(651,272)		5,052	5,860	(12,524)	20,247	20,027
Ending Balance	$ (103,507)	$ 800,260	$ 800,260	$ (90,983)						$ (12,524)

Accumulated change in equity from transactions and other events and circumstances from non-owner sources, net of tax effect, at period end. Excludes Net Income (Loss), and accumulated changes in equity from transactions resulting from investments by owners and distributions to owners. Includes foreign currency translation items, certain pension adjustments, unrealized gains and losses on certain investments in debt and equity securities, other than temporary impairment (OTTI) losses related to factors other than credit losses on available-for-sale and held-to-maturity debt securities that an entity does not intend to sell and it is not more likely than not that the entity will be required to sell before recovery of the amortized cost basis, as well as changes in the fair value of derivatives related to the effective portion of a designated cash flow hedge.

Reference 1: http://www.xbrl.org/2003/role/presentationRef

-Publisher FASB

-Name Accounting Standards Codification

-Topic 220

-SubTopic 10

-Section 45

-Paragraph 14

-URI http://asc.fasb.org/extlink&oid=20435746&loc=d3e681-108580

Reference 2: http://www.xbrl.org/2003/role/presentationRef

-Publisher FASB

-Name Accounting Standards Codification

-Topic 220

-SubTopic 10

-Section 45

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-URI http://asc.fasb.org/extlink&oid=20435746&loc=d3e637-108580

Reference 3: http://www.xbrl.org/2003/role/presentationRef

-Publisher FASB

-Name Accounting Standards Codification

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Reference 4: http://www.xbrl.org/2003/role/presentationRef

-Publisher AICPA

-Name Accounting Principles Board Opinion (APB)

-Number 12

-Paragraph 10

-LegacyDoc This reference is SUPERSEDED by the Accounting Standards Codification effective for interim and annual periods ending after September 15, 2009. This reference is included to help users transition from the previous accounting hierarchy and will be removed from future versions of this taxonomy.

Reference 5: http://www.xbrl.org/2003/role/presentationRef

-Publisher SEC

-Name Regulation S-X (SX)

-Number 210

-Section 02

-Paragraph 31

-Article 5

Reference 6: http://www.xbrl.org/2003/role/presentationRef

-Publisher FASB

-Name FASB Staff Position (FSP)

-Number FAS115-1/124-1

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-LegacyDoc This reference is SUPERSEDED by the Accounting Standards Codification effective for interim and annual periods ending after September 15, 2009. This reference is included to help users transition from the previous accounting hierarchy and will be removed from future versions of this taxonomy.

Reference 7: http://www.xbrl.org/2003/role/presentationRef

-Publisher FASB

-Name Statement of Financial Accounting Standard (FAS)

-Number 130

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-LegacyDoc This reference is SUPERSEDED by the Accounting Standards Codification effective for interim and annual periods ending after September 15, 2009. This reference is included to help users transition from the previous accounting hierarchy and will be removed from future versions of this taxonomy.

Reference 8: http://www.xbrl.org/2003/role/presentationRef

-Publisher SEC

-Name Regulation S-X (SX)

-Number 210

-Section 04

-Article 3

+ Details