Quarterly report pursuant to Section 13 or 15(d)

Derivative Instruments and Hedging Activities Credit Risk - Counterparty Exposure (Details)

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Derivative Instruments and Hedging Activities Credit Risk - Counterparty Exposure (Details) (USD $)
In Thousands, unless otherwise specified
Mar. 31, 2013
Dec. 31, 2012
Credit Derivatives [Line Items]    
Derivative Asset, Fair Value, Gross Asset $ 511,749 $ 462,080
Derivative Liability, Fair Value, Gross Liability 45,423 129,294
Collateral Securities Repledged, Delivered, or Used (160,655)  
Collateral Already Posted, Aggregate Fair Value $ 143,709