Financial Guarantee Insurance Contracts - Summary of Gross Premium Receivable Roll-Forward (Direct and Assumed Contracts) (Detail) (USD $) In Thousands, unless otherwise specified	5 Months Ended	4 Months Ended	12 Months Ended
Sep. 30, 2013 Successor Ambac [Member]	Apr. 30, 2013 Predecessor Ambac [Member]	Dec. 31, 2012 Predecessor Ambac [Member]
Insurance [Line Items]
Beginning premium receivable	$ 1,531,631	$ 1,620,621	$ 2,028,479
Premium payments received	(49,940)	(48,296)	(155,626)
Adjustments for changes in expected life of homogeneous pools and actual changes to contractual cash flows	(70,900)	(28,237)	(299,906)
Accretion of premium receivable discount	17,232	14,740	50,407
Uncollectible premiums	(14,800)	(634)	(28,031)
Other adjustments (including foreign exchange)	22,787	(26,563)	25,298
Ending premium receivable	$ 1,436,010	$ 1,531,631	$ 1,620,621

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Amount of increase (decrease) in the allowance for doubtful accounts.

+ References

No definition available.

+ Details

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- Definition

Amount of the premium receivable for financial guarantee insurance contracts reported in the statement of financial position. This element primarily would consist of those financial guarantee insurance contracts which premiums are to be collected over the contract period, but may, on occasion, include premiums which are to be collected in full at inception, but which straddle a financial reporting period.

+ References

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

-Publisher FASB

-Name Accounting Standards Codification

-Topic 944

-SubTopic 310

-Section 50

-Paragraph 3

-Subparagraph (c)(1),(5)

-URI http://asc.fasb.org/extlink&oid=6933075&loc=SL5748726-161290

+ Details

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Data Type:	xbrli:monetaryItemType
Balance Type:	debit
Period Type:	instant

- Definition

Amount of premium payments received during the period for premiums receivable on financial guarantee insurance contracts.

+ References

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

-Publisher FASB

-Name Accounting Standards Codification

-Topic 944

-SubTopic 310

-Section 50

-Paragraph 3

-Subparagraph (c)(2)

-URI http://asc.fasb.org/extlink&oid=6933075&loc=SL5748726-161290

+ Details

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- Definition

This element represents the accretion of the discount for premiums receivable on financial guarantee insurance contracts.

+ References

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

-Publisher FASB

-Name Accounting Standards Codification

-Topic 944

-SubTopic 310

-Section 50

-Paragraph 3

-Subparagraph (c)(4)(iii)

-URI http://asc.fasb.org/extlink&oid=6933075&loc=SL5748726-161290

+ Details

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Data Type:	xbrli:monetaryItemType
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- Definition

This element represents adjustments to the premium receivable related to financial guarantee insurance contracts due to changes in the period of the contract.

+ References

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

-Publisher FASB

-Name Accounting Standards Codification

-Topic 944

-SubTopic 310

-Section 50

-Paragraph 3

-Subparagraph (c)(4)(i)

-URI http://asc.fasb.org/extlink&oid=6933075&loc=SL5748726-161290

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- Definition

This element represents other adjustments to premiums receivable on financial guarantee insurance contracts.

+ References

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

-Publisher FASB

-Name Accounting Standards Codification

-Topic 944

-SubTopic 310

-Section 50

-Paragraph 3

-Subparagraph (c)(4)(iv)

-URI http://asc.fasb.org/extlink&oid=6933075&loc=SL5748726-161290

+ Details

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