Summary of Significant Accounting Policies (Details Textual) - USD ($) $ in Thousands	3 Months Ended				6 Months Ended
	Jun. 30, 2019	Mar. 31, 2019	Jun. 30, 2018	Mar. 31, 2018	Jun. 30, 2019	Jun. 30, 2018	Jan. 01, 2019	Dec. 31, 2018
Summary of Significant Accounting Policies
Total capitalized internal costs	$ 1,300		$ 1,000		$ 2,900	$ 2,400
Proved oil and gas properties	1,090,496				1,090,496			$ 925,865
Unproved oil and gas properties	49,866				49,866			56,715
Furniture, fixtures, and other equipment	3,855				3,855			3,520
Less - Accumulated depreciation, depletion, and amortization	(330,638)				(330,638)			(284,804)
Net Furniture, Fixtures and other equipment	813,579				813,579			701,296
Write-down of oil and gas properties	0		0		0	0
Allowance for doubtful accounts receivable, current	100				100			100
Accounts receivable, gross	25,500				25,500			36,900
Accounts receivable related to joint interest owners	800				800			5,600
Severance tax receivable	4,100				4,100			2,400
Other receivables	4,400				$ 4,400			1,600
Percentage of working interest in wells					100.00%
Total amount of supervision fees charged to wells	1,300		1,100		$ 2,600	2,200
Partial Release of Valuation Allowance	21,200
Income Tax Expense (Benefit)	(20,735)		328		(20,503)	328
State and Local Income Tax Expense (Benefit), Continuing Operations	300				500
Oil and gas sales	74,703		$ 51,347		146,768	104,099
Trade accounts payable	18,560				18,560			32,683
Accrued operating expenses	3,410				3,410			3,549
Accrued payroll costs	3,175				3,175			4,785
Asset retirement obligation - current portion	270				270			302
Accrued non-income based taxes	4,279				4,279			3,583
Accrued corporate and legal fees	239				239			534
Other payables	3,387				3,387			3,485
Accounts payable and accrued liabilities	$ 33,320				$ 33,320			48,921
Purchase of treasury stock (shares)	3,877	11,076	4,649	10,458	14,953
Operating Lease, Right-of-Use Asset	$ 12,568				$ 12,568		$ 2,200	$ 0
Right-of-Use Asset Obtained in Exchange for Operating Lease Liability	11,500
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
Oil sales [Member]
Summary of Significant Accounting Policies
Oil and gas sales	24,940		$ 9,638		$ 39,547	21,078
Natural gas sales [Member]
Summary of Significant Accounting Policies
Oil and gas sales	43,587		36,369		94,874	72,136
NGL sales [Member]
Summary of Significant Accounting Policies
Oil and gas sales	6,166		5,339		12,319	10,900
Other sales [Member]
Summary of Significant Accounting Policies
Oil and gas sales	$ 10		$ 0		$ 28	$ (14)