Annual report pursuant to Section 13 and 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
Dec. 31, 2012
Dec. 31, 2011
Credit Derivatives [Line Items]    
Derivative Asset, Fair Value, Gross Asset $ 462,080 $ 251,856
Derivative Liability, Fair Value, Gross Liability 129,294 49,080
Collateral Securities Repledged, Delivered, or Used (114,065)  
Collateral Already Posted, Aggregate Fair Value $ 212,807