v2.4.0.6
Derivative Instruments (Gain (Loss) Recognized In The Consolidated Statements Of Operations Related To Its Derivative Instruments) (Details) (USD $)
In Thousands, unless otherwise specified
3 Months Ended
Mar. 31, 2013
Mar. 31, 2012
Derivative Instruments, Gain (Loss) [Line Items]    
Amount of gain (loss) recognized on derivatives $ 20,703 $ (27,684)
Net investment income (loss) [Member] | Interest Rate Futures [Member]
   
Derivative Instruments, Gain (Loss) [Line Items]    
Amount of gain (loss) recognized on derivatives 2 1,030
Net investment income (loss) [Member] | Credit Default Swap [Member]
   
Derivative Instruments, Gain (Loss) [Line Items]    
Amount of gain (loss) recognized on derivatives 434 558
Net foreign exchange gains (losses) [Member] | Foreign Currency Forward Contracts, Underwriting and Non-investment Operations [Member]
   
Derivative Instruments, Gain (Loss) [Line Items]    
Amount of gain (loss) recognized on derivatives 2,388 [1] 3,552 [1]
Net foreign exchange gains (losses) [Member] | Foreign Currency Forward Contracts, Investment Operations [Member]
   
Derivative Instruments, Gain (Loss) [Line Items]    
Amount of gain (loss) recognized on derivatives 1,678 [2] (4,248) [2]
Net foreign exchange gains (losses) [Member] | Foreign Currency Forward Contracts, Energy And Risk Operations [Member]
   
Derivative Instruments, Gain (Loss) [Line Items]    
Amount of gain (loss) recognized on derivatives 1,545 [3] 137 [3]
Other income (loss) [Member] | Energy And Weather Contracts [Member]
   
Derivative Instruments, Gain (Loss) [Line Items]    
Amount of gain (loss) recognized on derivatives $ 14,656 $ (28,713)
[1] Contracts used to manage foreign currency risks in underwriting and non-investment operations.
[2] Contracts used to manage foreign currency risks in investment operations.
[3] Contracts used to manage foreign currency risks in energy and risk operations.