Reconciliation of Level 3 Fair Value Measurements (Details) - Derivative Financial Instrument Net Assets - USD ($) $ in Thousands	3 Months Ended		9 Months Ended
	Sep. 30, 2019	Sep. 30, 2018	Sep. 30, 2019	Sep. 30, 2018
Roll-forward of Level 3 Assets
Fair Value, net assets (liabilities), beginning of period	$ 22,504	$ (19,100)	$ 58,329	$ (9,687)
Fair Value, net assets (liabilities), end of period	30,905	(28,862)	30,905	(28,862)
Commodity Price Risk Management (loss), net
Roll-forward of Level 3 Assets
Changes in fair value included in statement of operations line item:	10,846	(16,175)	(22,077)	(23,029)
Settlements included in statement of operations line items:	(2,445)	6,413	(5,347)	3,854
Net change in fair value of unsettled derivatives included in statement of operations line item	$ 6,787	$ (7,451)	$ (11,620)	$ (4,229)