Derivative Instruments (Details) (USD $) In Thousands, unless otherwise specified	Dec. 31, 2014	Dec. 31, 2013
Derivatives
Derivative assets, Fair Value	$ 3,136	$ 13,000
Derivative liabilities, Fair Value	(62,198)	(28,217)
Linked Transactions \| Non-Hedging \| Assets
Derivatives
Linked Transactions, Fair Value	398,336	28,181
Swaps \| Hedging \| Assets \| Non-cleared legacy swaps
Derivatives
Derivative assets, Notional Amount	450,000
Derivative assets, Fair Value	3,136	4,925
Swaps \| Hedging \| Assets \| Cleared swaps
Derivatives
Derivative assets, Notional Amount	0
Derivative assets, Fair Value	0	8,075
Swaps \| Hedging \| Liability \| Non-cleared legacy swaps
Derivatives
Derivative liabilities, Notional Amount	760,170
Derivative liabilities, Fair Value	(4,263)	(24,437)
Swaps \| Hedging \| Liability \| Cleared swaps
Derivatives
Derivative liabilities, Notional Amount	2,550,000
Derivative liabilities, Fair Value	$ (57,935)	$ (3,780)

Fair value, after offset of derivative liability, of 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, before offset against an obligation to return collateral under a master netting arrangement. Includes assets elected not to be offset. Excludes assets not subject to a master netting arrangement.

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Fair value, after offset of derivative asset, of financial liability or 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, elected not to be and before offset against a right to receive collateral under a master netting arrangement. Includes liabilities elected not to be offset. Excludes liabilities not subject to a master netting arrangement.

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