Physical Delivery Contracts and Gas Derivatives (Details 3) - USD ($) $ in Thousands	Jun. 30, 2017	Dec. 31, 2016
Commodity derivative assets:
Current assets	$ 604
Other long-term assets	487
Total derivative assets	1,091
Commodity derivative liabilities:
Current liability		1,341
Non-current liabilities		591
Total derivative liabilities		$ 1,932
Gross Recognized Assets/Liabilities [Member]
Commodity derivative assets:
Current assets	844
Other long-term assets	593
Total derivative assets	1,437
Commodity derivative liabilities:
Current liability	240
Non-current liabilities	106
Total derivative liabilities	346
Gross Amounts Offset [Member]
Commodity derivative assets:
Current assets	(240)
Other long-term assets	(106)
Total derivative assets	(346)
Commodity derivative liabilities:
Current liability	(240)
Non-current liabilities	(106)
Total derivative liabilities	(346)
Net Recognized Fair Value Assets/Liabilities [Member]
Commodity derivative assets:
Current assets	604
Other long-term assets	487
Total derivative assets	1,091
Commodity derivative liabilities:
Current liability
Non-current liabilities
Total derivative liabilities