Derivative Financial Instruments Impact of Netting Agreements (Details) - USD ($) $ in Thousands	Mar. 31, 2018	Dec. 31, 2017
Derivative Asset:
Derivative assets, gross	$ 28,610	$ 14,338
Effect of master netting agreements	(27,971)	(14,173)
Derivative asset, net	639	165
Derivative Liability:
Derivative liability, gross	137,109	101,645
Effect of master netting agreements	(27,971)	(14,173)
Derivative liability, net	$ 109,138	$ 87,472

Fair value, after the effects of master netting arrangements, of a 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. Includes assets not subject to a master netting arrangement and not elected to be offset.

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