Reconciliation of Level 3 Fair Value Measurements (Details) - Derivative Financial Instrument Net Assets - USD ($) $ in Thousands	3 Months Ended
	Mar. 31, 2018	Mar. 31, 2017
Roll-forward of Level 3 Assets
Fair Value, net assets, beginning of period	$ (9,687)	$ (9,574)
Fair Value, net assets, end of period	(8,833)	2,316
Commodity Price Risk Management (loss), net
Roll-forward of Level 3 Assets
Changes in fair value included in statement of operations line item:	(2,152)	13,360
Settlements included in statement of operations line items:	3,006	(1,470)
Net change in fair value of unsettled derivatives included in statement of operations line item	$ 1,205	$ 11,427