Reorganization Under Chapter 11 - Additional Information (Detail) (Ambac Financial Group, Inc Parent Company Only [Member], USD $) In Thousands, unless otherwise specified	3 Months Ended
Mar. 31, 2013
Ambac Financial Group, Inc Parent Company Only [Member]
Fresh-Start Adjustment [Line Items]
Discontinued Liabilities subject to compromise	$ 232,556
Liabilities subject to compromise contractual interest on debt	$ 20,660

The amount of contractual interest expense on prepetition liabilities not included in the statement of operations.

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

-Publisher FASB

-Name Accounting Standards Codification

-Topic 852

-SubTopic 10

-Section 55

-Paragraph 3

-URI http://asc.fasb.org/extlink&oid=29642632&loc=d3e56145-112766

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

-Publisher FASB

-Name Accounting Standards Codification

-Topic 852

-SubTopic 10

-Section 50

-Paragraph 3

-URI http://asc.fasb.org/extlink&oid=6918054&loc=d3e56068-112765

Name:	us-gaap_ContractualInterestExpenseOnPrepetitionLiabilitiesNotRecognizedInStatementOfOperations
Namespace Prefix:	us-gaap_
Data Type:	xbrli:monetaryItemType
Balance Type:	debit
Period Type:	duration