Supplemental Disclosures (Details 1) - USD ($) $ in Thousands	6 Months Ended
	Jun. 30, 2015	Jun. 30, 2014
Supplemental disclosures of cash flow information
Cash paid for interest expense, net of amounts capitalized	$ 2,263	$ 3,058
Asset retirement obligations related to mineral properties	1,212	2,343
Asset retirement obligations related to support equipment and facilities	41	132
(Decrease) increase in liabilities for oil and natural gas properties capital expenditures	(9,909)	34,444
Increase in liabilities for support equipment and facilities	3,859	293
Stock-based compensation expense recognized as liability	583	1,200
Transfer of inventory from oil and natural gas properties	$ 456	$ 133