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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
	Mar. 31, 2013	Mar. 31, 2012
Segment Information [Line Items]
Gross Premiums Written	$ (3,530)	$ (92,594)
Net Premiums Earned	100,256	94,950
Net change in fair value of credit derivatives	12,787	(7,222)
United States [Member]
Segment Information [Line Items]
Gross Premiums Written	(8,716)	(92,724)
Net Premiums Earned	81,057	72,985
Net change in fair value of credit derivatives	16,530	(3,451)
United Kingdom [Member]
Segment Information [Line Items]
Gross Premiums Written	8,507	6,414
Net Premiums Earned	13,754	15,041
Net change in fair value of credit derivatives	(2,175)	(3,624)
Other international [Member]
Segment Information [Line Items]
Gross Premiums Written	(3,321)	(6,284)
Net Premiums Earned	5,445	6,924
Net change in fair value of credit derivatives	$ (1,568)	$ (147)

X

- Definition

Net change in fair value of credit derivatives.

+ References

No definition available.

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X

- Definition

Premiums written for direct and assumed insurance contracts.

+ References

No definition available.

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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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