Derivative Instruments (Consolidated Balance Sheets And Fair Value Of The Principal Derivative Instruments) (Details) (USD $) In Thousands | Sep. 30, 2011 | Dec. 31, 2010 | ||||||||||
|---|---|---|---|---|---|---|---|---|---|---|---|---|
| Derivative Asset, Total | $ 34,869 | $ 74,714 | ||||||||||
| Derivative Liabilities, Total | 32,149 | 18,917 | ||||||||||
Derivative Assets [Member] | Other Assets [Member] | ||||||||||||
| Interest rate futures | 246 | 2,459 | ||||||||||
| Foreign currency forward contracts | 6,341 | [1] | ||||||||||
| Foreign currency forward contracts | 9,820 | [2] | ||||||||||
| Foreign currency forward contracts | 948 | [3] | ||||||||||
| Platinum warrant | 44,925 | |||||||||||
| Credit default swaps | 3,064 | |||||||||||
| Energy and weather contracts | 23,855 | [4] | 17,925 | [4] | ||||||||
Derivative Liabilities [Member] | Other Liabilities [Member] | ||||||||||||
| Interest rate futures | 1,019 | 719 | ||||||||||
| Foreign currency forward contracts | 9,281 | [1] | ||||||||||
| Foreign currency forward contracts | 3,141 | [2] | ||||||||||
| Foreign currency forward contracts | 44 | [3] | ||||||||||
| Credit default swaps | 537 | |||||||||||
| Energy and weather contracts | $ 21,312 | [4] | $ 15,013 | [4] | ||||||||
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