Derivative Instruments (Details) - USD ($) $ in Thousands		Dec. 31, 2015	Dec. 31, 2014
Derivatives
Derivative assets, Fair Value		$ 1,127	$ 3,136
Linked Transactions | Non-Hedging | Assets
Derivatives
Linked Transactions, Fair Value			398,336
Swaps | Hedging | Assets | Non-cleared legacy swaps
Derivatives
Derivative assets, Notional Amount	[1]	450,000	450,000
Derivative assets, Fair Value	[1]	1,127	3,136
Swaps | Hedging | Liability | Non-cleared legacy swaps
Derivatives
Derivative liabilities, Notional Amount	[1]	50,000	760,170
Derivative liabilities, Fair Value	[1]	(59)	(4,263)
Swaps | Hedging | Liability | Cleared swaps
Derivatives
Derivative liabilities, Notional Amount	[2]	2,550,000	2,550,000
Derivative liabilities, Fair Value	[2]	$ (70,467)	$ (57,935)

[1] Non-cleared legacy Swaps include Swaps executed and settled bilaterally with counterparties without the use of an organized exchange or central clearing house.

[2] Cleared Swaps include Swaps executed bilaterally with a counterparty in the over-the-counter market but then novated to a central clearing house, whereby the central clearing house becomes the counterparty to both of the original counterparties.