Summary of Significant Accounting Policies (Details) - USD ($) $ in Thousands	Jun. 30, 2018	Dec. 31, 2017	Jun. 30, 2017	Dec. 31, 2016
Property and Equipment
Proved oil and gas properties	$ 738,780	$ 658,519
Unproved oil and gas properties	53,865	50,377
Furniture, fixtures, and other equipment	3,407	3,270
Less - Accumulated depreciation, depletion, and amortization	(242,997)	(216,769)
Net Furniture, Fixtures and other equipment	553,055	495,397
Accounts Payable and Accrued Liabilities
Trade accounts payable	16,015	20,884
Accrued operating expenses	2,316	3,490
Accrued compensation costs	2,945	5,334
Asset retirement obligation - current portion	303	2,109
Accrued non-income based taxes	5,137	3,898
Accrued corporate and legal fees	3,120	2,784
Other payables	5,514	5,938
Total accounts payable and accrued liabilities	35,350	44,437
Cash, Cash Equivalents, Restricted Cash and Restricted Cash Equivalents [Abstract]
Cash and cash equivalents	6,611	7,806	$ 6,627
Long-term restricted cash	220	220	179
Cash, Cash Equivalents, Restricted Cash and Restricted Cash Equivalents	$ 6,831	$ 8,026	$ 6,806	$ 497