Derivative Instruments and Hedging Activities - Offsetting Assets (Details) - Commodity derivatives - USD ($) $ in Thousands	Sep. 30, 2017	Dec. 31, 2016
Assets
Gross Amounts of Recognized Assets	$ 18,805	$ 79,649
Gross Amounts Offset in the Balance Sheet	(9,607)	(20,805)
Net Amounts of Assets Presented in the Balance Sheet	9,198	58,844
Net Amount	$ 9,198	$ 58,844

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.

Reference 1: http://www.xbrl.org/2003/role/presentationRef
-Publisher FASB
-Name Accounting Standards Codification
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Reference 2: http://www.xbrl.org/2003/role/presentationRef
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Reference 3: http://www.xbrl.org/2003/role/presentationRef
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