Derivative Instruments and Hedging Activities - Offsetting Liabilities (Details) - Commodity derivatives - USD ($) $ in Thousands	Sep. 30, 2017	Dec. 31, 2016
Liabilities
Gross Amounts of Recognized Liabilities	$ (30,658)	$ (36,664)
Gross Amounts Offset in the Balance Sheet	9,607	20,805
Net Amounts of Liabilities Presented in the Balance Sheet	(21,051)	(15,859)
Net Amount	$ (21,051)	$ (15,859)

Fair value, after the effects of master netting arrangements, of a 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. Includes liabilities 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
-Topic 210
-SubTopic 20
-Section 55
-Paragraph 10
-URI http://asc.fasb.org/extlink&oid=51825145&loc=SL20226008-175313

Reference 2: http://www.xbrl.org/2003/role/presentationRef
-Publisher FASB
-Name Accounting Standards Codification
-Topic 825
-SubTopic 10
-Section 50
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Reference 3: http://www.xbrl.org/2003/role/presentationRef
-Publisher FASB
-Name Accounting Standards Codification
-Topic 210
-SubTopic 20
-Section 50
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Reference 4: http://www.xbrl.org/2003/role/presentationRef
-Publisher FASB
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Reference 5: http://www.xbrl.org/2003/role/presentationRef
-Publisher FASB
-Name Accounting Standards Codification
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Reference 6: http://www.xbrl.org/2003/role/presentationRef
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-Section 45
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-URI http://asc.fasb.org/extlink&oid=6945355&loc=d3e41228-113958

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Balance Type:	credit
Period Type:	instant