Derivative Financial Instruments - Cash Receipts on Derivative Settlements, Net Included within Net Cash Provided by (Used in) Operating Activities (Details)

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Derivative Financial Instruments - Cash Receipts on Derivative Settlements, Net Included within Net Cash Provided by (Used in) Operating Activities (Details) - USD ($) $ in Thousands	6 Months Ended
	Jun. 30, 2017	Jun. 30, 2016
Derivative Instruments And Hedging Activities Disclosure [Abstract]
Cash receipts on derivative settlements, net	$ 2,208	$ 4,746