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
Jun. 30, 2013
Dec. 31, 2012
Credit Derivatives [Line Items]    
Derivative Asset, Fair Value, Gross Asset $ 699,351 $ 462,080
Derivative Liability, Fair Value, Gross Liability 46,028 129,294
Collateral Securities Repledged, Delivered, or Used (271,943)  
Collateral Already Posted, Aggregate Fair Value $ 82,641