Commodity Derivatives (Details 3) - USD ($) $ in Thousands	Dec. 31, 2018	Dec. 31, 2017
Commodity derivative assets:
Commodity derivative asset	$ 3,517	$ 215
Other long-term assets	3,505	10
Commodity derivative liabilities:
Commodity derivative
Commodity derivative: non-current
Gross Recognized Assets/Liabilities [Member]
Commodity derivative assets:
Commodity derivative asset	4,605	624
Other long-term assets	4,691	250
Total derivative assets	9,296	874
Commodity derivative liabilities:
Commodity derivative	(1,088)	(409)
Commodity derivative: non-current	(1,186)	(240)
Total derivative liabilities	(2,274)	(649)
Gross Amounts Offset [Member]
Commodity derivative assets:
Commodity derivative asset	(1,088)	(409)
Other long-term assets	(1,186)	(240)
Total derivative assets	(2,274)	(649)
Commodity derivative liabilities:
Commodity derivative	1,088	409
Commodity derivative: non-current	1,186	240
Total derivative liabilities	2,274	649
Net Recognized Fair Value Assets/Liabilities [Member]
Commodity derivative assets:
Commodity derivative asset	3,517	215
Other long-term assets	3,505	10
Total derivative assets	7,022	225
Commodity derivative liabilities:
Commodity derivative
Commodity derivative: non-current
Total derivative liabilities