Supplemental Disclosures (Details 1) - USD ($) $ in Thousands	12 Months Ended
	Dec. 31, 2017	Dec. 31, 2016	Dec. 31, 2015
Supplemental disclosures of cash flow information
Cash paid for income taxes	$ 0	$ 2,895	$ 506
Cash paid for interest expense, net of amounts capitalized	32,760	27,464	16,154
Increase in asset retirement obligations related to mineral properties	4,385	3,817	2,510
(Decrease) increase in asset retirement obligations related to support equipment and facilities	(60)	222	383
Increase (decrease) in liabilities for oil and natural gas properties capital expenditures	48,929	1,775	(30,683)
(Decrease) increase in liabilities for support equipment and facilities	(955)	(588)	12,076
Issuance of restricted stock units for director and advisor services	0	992	584
Stock-based compensation expense recognized as liability	362	569	79
(Decrease) increase in liabilities for accrued cost to issue equity	(343)	343	0
Transfer of inventory (to) from oil and natural gas properties	(374)	395	615
Transfer of inventory to other property and equipment	$ (317)	$ 0	$ 0