Investments (Detail) - Summary of structured project finance loans (USD $) In Thousands, unless otherwise specified	3 Months Ended	12 Months Ended
Mar. 31, 2012	Dec. 31, 2011
Aggregate loan value (in Dollars)	$ 39,786	$ 49,650
Aggregate loan net carrying value (in Dollars)	33,886	40,483
Opening allowance for loan losses (in Dollars)	(9,167)	(9,167)
Amounts charged off during the period (in Dollars)	3,267	0
Closing allowance for loan losses (in Dollars)	$ (5,900)	$ (9,167)
Number of individual loan participations	5	6
Number of individual loan participations relating to the allowance for loan losses	2	2
Weighted average contractual term to maturity	1.41 years	2.12 years
Weighted average credit rating	BB	BB-
Range of individual credit ratings	BB+ to B+	BB+ to CCC

For loans and debt securities, 1) for which at acquisition it was probable that the investor would be unable to collect all contractually required payments receivable, and 2) for which it is further probable that the investor will not be able to collect all cash flows expected at acquisition (plus any additional cash flows expected due to changes in estimate after acquisition), the allowance for credit losses recorded to reflect the impairment since acquisition.

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

-Publisher FASB

-Name Statement of Financial Accounting Standard (FAS)

-Number 114

-Paragraph 20

-Subparagraph a(1)

-LegacyDoc This reference is SUPERSEDED by the Accounting Standards Codification effective for interim and annual periods ending after September 15, 2009.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.

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

-Publisher AICPA

-Name Statement of Position (SOP)

-Number 03-3

-Paragraph 15

-LegacyDoc This reference is SUPERSEDED by the Accounting Standards Codification effective for interim and annual periods ending after September 15, 2009.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.

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

-Publisher FASB

-Name Accounting Standards Codification

-Topic 310

-SubTopic 10

-Section 50

-Paragraph 18

-URI http://asc.fasb.org/extlink&oid=7512638&loc=d3e5275-111524

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

-Publisher FASB

-Name Accounting Standards Codification

-Topic 310

-SubTopic 10

-Section 50

-Paragraph 15

-Subparagraph (a)(1)

-URI http://asc.fasb.org/extlink&oid=7512638&loc=d3e5212-111524

+ Details

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- Definition

The recorded amount of loans and debt securities, with evidence of deterioration of credit quality since origination that were acquired by completion of a transfer for which it was probable, at acquisition, that the investor would be unable to collect all contractually required payments receivable. They are deemed to be impaired since the acquisition and an allowance for credit losses has been recorded. Disclosure is gross of the allowance.

+ References

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- Definition

Amount of certain loans acquired in transfer accounted charged off.

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Net carrying amount of certain loans acquired in transfer accounted.

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- Definition

Number of individual loan participations.

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- Definition

Number of individual loan participations relating to the allowance for loan losses.

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- Definition

Range of individual credit ratings.

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- Definition

This element represents the remaining weighted average contractual term to maturity during the period.

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- Definition

Weighted average credit rating of deals within the structured project finance related transactions within Other Investments.

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