Derivative Instruments - Balance sheet offsetting (Details) (USD $) In Thousands, unless otherwise specified	Mar. 31, 2014	Dec. 31, 2013
Derivative assets:
Gross amounts recognized in balance sheet	$ 8,858	$ 27,487
Gross amounts offset in balance sheet	0	1,342
Net amounts in the balance sheet	8,858	26,145
Gross amounts not offset in the balance sheet - financial instruments	0	0
Gross amounts not offset in the balance sheet - cash collateral	0	0
Derivative Asset	8,858	26,145
Derivative liabilities:
Gross amounts recognized in balance sheet	61,367	105,485
Gross amounts offset in balance sheet	0	1,342
Net amounts in the balance sheet	61,367	104,143
Gross amounts not offset in the balance sheet - financial instruments	0	0
Gross amounts not offset in the balance sheet - cash collateral	1,791	19,847
Derivative Liability	$ 59,576	$ 84,296

Fair value of liability associated with financial asset or other contract with one or more underlyings, notional amount or payment provision or both, and the contract can be net settled by means outside the contract or delivery of an asset.

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