Derivative Instruments (Gain (Loss) Recognized In The Consolidated Statements Of Operations Related To Its Derivative Instruments) (Details) (USD $) In Thousands | 3 Months Ended | 9 Months Ended | ||||||||||||
|---|---|---|---|---|---|---|---|---|---|---|---|---|---|---|
Sep. 30, 2011 | Sep. 30, 2010 | Sep. 30, 2011 | Sep. 30, 2010 | |||||||||||
| Derivative Instruments, Gain (Loss) Recognized in Income, Net | $ (17,819) | $ (7,021) | $ (16,913) | $ 34,446 | ||||||||||
Interest Rate Contract [Member] | Investment Income [Member] | ||||||||||||||
| Derivative Instruments, Gain (Loss) Recognized in Income, Net | (15,235) | 5,806 | (23,582) | 5,341 | ||||||||||
Energy And Weather Contracts [Member] | Other Income [Member] | ||||||||||||||
| Derivative Instruments, Gain (Loss) Recognized in Income, Net | 2,272 | (11) | 12,201 | 7,174 | ||||||||||
Other Income [Member] | Credit Default Swap [Member] | ||||||||||||||
| Derivative Instruments, Gain (Loss) Recognized in Income, Net | (4,290) | 310 | (3,148) | 223 | ||||||||||
Other Income [Member] | Platinum Warrant [Member] | ||||||||||||||
| Derivative Instruments, Gain (Loss) Recognized in Income, Net | 14,352 | 2,975 | 8,987 | |||||||||||
Energy And Risk Operations Foreign Currency Contracts [Member] | Foreign Currency Loss [Member] | ||||||||||||||
| Derivative Instruments, Gain (Loss) Recognized in Income, Net | 775 | [1] | (790) | [1] | 127 | [1] | 126 | [1] | ||||||
Foreign Currency Loss [Member] | Underwriting Operations Related Foreign Currency Contracts [Member] | ||||||||||||||
| Derivative Instruments, Gain (Loss) Recognized in Income, Net | (15,927) | [2] | (1,160) | [2] | 1,080 | [2] | (686) | [2] | ||||||
Foreign Currency Loss [Member] | Investment Operations Foreign Currency Contracts [Member] | ||||||||||||||
| Derivative Instruments, Gain (Loss) Recognized in Income, Net | $ 14,586 | [3] | $ (25,528) | [3] | $ (6,566) | [3] | $ 13,281 | [3] | ||||||
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