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Segment Information - Schedule of Gross Premiums Written, Net Premiums Earned and Net Change in Fair Value of Credit Derivatives (Detail) (USD $) In Thousands, unless otherwise specified	3 Months Ended		9 Months Ended
	Sep. 30, 2012	Sep. 30, 2011	Sep. 30, 2012	Sep. 30, 2011
Segment Information [Line Items]
Gross Premiums Written	$ (55,310)	$ 242,573	$ (175,777)	$ (125,712)
Net Premiums Earned	113,074	102,055	311,066	293,125
Net Change in Fair Value of Credit Derivatives	27,440	4,505	12,803	19,889
United States [Member]
Segment Information [Line Items]
Gross Premiums Written	(40,748)	26,998	(165,408)	(328,181)
Net Premiums Earned	92,132	82,291	235,672	232,420
Net Change in Fair Value of Credit Derivatives	15,845	3,223	7,577	13,741
United Kingdom [Member]
Segment Information [Line Items]
Gross Premiums Written	(1,060)	187,895	11,325	198,778
Net Premiums Earned	14,763	12,220	55,355	35,006
Net Change in Fair Value of Credit Derivatives	716	(602)	(3,721)	251
Other International [Member]
Segment Information [Line Items]
Gross Premiums Written	(13,502)	27,680	(21,694)	3,691
Net Premiums Earned	6,179	7,544	20,039	25,699
Net Change in Fair Value of Credit Derivatives	$ 10,879	$ 1,884	$ 8,947	$ 5,897

X

- Definition

Net change in fair value of credit derivatives.

+ References

No definition available.

+ Details

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X

- Definition

Premiums written for direct and assumed insurance contracts.

+ References

No definition available.

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- Details

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X

- Definition

Premiums earned on the income statement for all insurance and reinsurance contracts after subtracting any amounts ceded to another insurer and adding premiums assumed from other insurers.

+ References

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

-Publisher FASB

-Name Accounting Standards Codification

-Topic 942

-SubTopic 225

-Section S99

-Paragraph 1

-Subparagraph (SX 210.9-04.13(c))

-URI http://asc.fasb.org/extlink&oid=6879574&loc=d3e536633-122882



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

-Publisher FASB

-Name Accounting Standards Codification

-Topic 944

-SubTopic 225

-Section S99

-Paragraph 1

-Subparagraph (SX 210.7-04.1)

-URI http://asc.fasb.org/extlink&oid=6879464&loc=d3e573970-122913



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

-Publisher SEC

-Name Regulation S-X (SX)

-Number 210

-Section 04

-Paragraph 1

-Article 7



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

-Publisher FASB

-Name Statement of Financial Accounting Standard (FAS)

-Number 113

-Paragraph 27

-Subparagraph a, b

-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.

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