Summary of Significant Accounting Policies (Details Textual) $ in Thousands	3 Months Ended		9 Months Ended		12 Months Ended
	Sep. 30, 2018 USD ($)	Sep. 30, 2017 USD ($)	Sep. 30, 2018 USD ($) shares	Sep. 30, 2017 USD ($)	Dec. 31, 2017 USD ($) shares	Nov. 06, 2018 USD ($)	Apr. 20, 2018 USD ($)	Dec. 22, 2017	Dec. 31, 2016 USD ($)
Summary of Significant Accounting Policies
Total capitalized internal costs	$ 1,200	$ 1,300	$ 3,600	$ 3,600
Proved oil and gas properties	833,202		833,202		$ 658,519
Unproved oil and gas properties	54,986		54,986		50,377
Furniture, fixtures, and other equipment	3,520		3,520		3,270
Less - Accumulated depreciation, depletion, and amortization	(261,763)		(261,763)		(216,769)
Property and Equipment, Net	629,945		629,945		495,397
Write-down of oil and gas properties	0	0	0	0
Allowance for doubtful accounts receivable, current	100		100		100
Accounts receivable, gross	24,200		24,200		20,100
Accounts receivable related to joint interest owners	3,300		3,300		2,100
Severance tax receivable	900		900		2,100
Other receivables	2,700		$ 2,700		3,000
Percentage of working interest in wells			100.00%
Total amount of supervision fees charged to wells	1,200	1,100	$ 3,400	3,500
Income Tax Expense (Benefit)	220	0	549	0
Previous Federal Corporate Tax Rate								0.35
New Federal Corporate Tax Rate								0.21
Trade accounts payable	26,040		26,040		20,884
Accrued operating expenses	3,062		3,062		3,490
Accrued payroll costs	3,860		3,860		5,334
Asset retirement obligation - current portion	469		469		2,109
Accrued non-income based taxes	8,237		8,237		3,898
Accrued corporate and legal fees	2,547		2,547		2,784
Other payables	3,893		3,893		5,938
Accounts payable and accrued liabilities	48,108		48,108		44,437
Cash and cash equivalents	4,542	12,861	4,542	12,861	7,806
Restricted Cash	0	220	0	220	220
Cash, Cash Equivalents, Restricted Cash and Restricted Cash Equivalents	$ 4,542	$ 13,081	$ 4,542	$ 13,081	$ 8,026				$ 497
Purchase of treasury stock (shares) | shares			15,107		28,279
Other Commitment					$ 6,200
Lessee, Operating Lease, Term of Contract					3 years
Office Lease [Member]
Summary of Significant Accounting Policies
Other Commitment					$ 2,000
Minimum [Member]
Summary of Significant Accounting Policies
Estimated useful lives of property			2 years
Maximum [Member]
Summary of Significant Accounting Policies
Estimated useful lives of property			20 years
New Credit Facility [Member] | Line of Credit [Member]
Summary of Significant Accounting Policies
Line of Credit Facility, Current Borrowing Capacity							$ 330,000
New Credit Facility [Member] | Line of Credit [Member] | Subsequent Event [Member]
Summary of Significant Accounting Policies
Line of Credit Facility, Current Borrowing Capacity						$ 410,000