Investments - Summary of Net Investment Income (Detail) (Successor [Member], USD $) In Thousands, unless otherwise specified	3 Months Ended
Mar. 31, 2015	Mar. 31, 2014
Investment [Line Items]
Net Realized and Unrealized Gain (Loss) on Trading Securities	$ 7,819	$ 1,994
Trading Securities, Realized Gain (Loss)	1,564	(455)
Fixed income securities	65,585	71,231
Short-term investments	42	57
Loans	132	117
Investment expense	(2,427)	(2,598)
Securities available-for-sale and short-term	63,332	68,807
Other investments	9,651ambc_OtherInvestmentsIncome	1,994ambc_OtherInvestmentsIncome
Total net investment income	72,983us-gaap_NetInvestmentIncome	70,801us-gaap_NetInvestmentIncome
Gains (losses) on securities held as of reporting date [Member]
Investment [Line Items]
Other investments	$ 6,255	$ 2,449

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Investment Income Interest On Debt Securities

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Investment Income Interest On Loans Receivable

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Other Investments Income

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- Definition

Amount of operating dividend and interest income, including amortization and accretion of premiums and discounts, on available-for-sale securities.

+ References

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

-Publisher FASB

-Name Accounting Standards Codification

-Glossary Available-for-Sale Securities

-URI http://asc.fasb.org/extlink&oid=6505594

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

-Publisher FASB

-Name Accounting Standards Codification

-Topic 942

-SubTopic 225

-Section S99

-Paragraph 1

-Subparagraph (SX 210.9-04.2)

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-Publisher SEC

-Name Regulation S-X (SX)

-Number 210

-Section 04

-Paragraph 2

-Article 9

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-Publisher FASB

-Name Accounting Standards Codification

-Topic 320

-SubTopic 10

-Section 35

-Paragraph 4

-URI http://asc.fasb.org/extlink&oid=27723805&loc=d3e24721-111560

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Amount of expenses related to the generation of investment income.

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-Publisher FASB

-Name Accounting Standards Codification

-Topic 944

-SubTopic 225

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Amount, after investment expense, of income earned from investments in securities and real estate. Includes, but is not limited to, real estate investment, policy loans, dividends, and interest. Excludes realized gain (loss) on investments.

+ References

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

-Publisher SEC

-Name Regulation S-X (SX)

-Number 210

-Section 16

-Article 12

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-Topic 944

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- Definition

The sum of the realized and unrealized net gain (loss) on trading securities during the period.

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

-Publisher FASB

-Name Accounting Standards Codification

-Glossary Trading Securities

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- Definition

This item represents the gain (loss) realized during the period from the sale of trading securities.

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-Number 210

-Section 03

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-Topic 225

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