Summary of Significant Accounting Policies (Details Textual) - USD ($) $ in Thousands	3 Months Ended						9 Months Ended
	Sep. 30, 2019	Jun. 30, 2019	Mar. 31, 2019	Sep. 30, 2018	Jun. 30, 2018	Mar. 31, 2018	Sep. 30, 2019	Sep. 30, 2018	Oct. 17, 2019	Jan. 01, 2019	Dec. 31, 2018	Nov. 06, 2018
Summary of Significant Accounting Policies
Total capitalized internal costs	$ 1,200			$ 1,200			$ 4,100	$ 3,600
Proved oil and gas properties	1,146,106						1,146,106				$ 925,865
Unproved oil and gas properties	43,066						43,066				56,715
Furniture, fixtures, and other equipment	4,499						4,499				3,520
Less - Accumulated depreciation, depletion, and amortization	(355,574)						(355,574)				(284,804)
Net Furniture, Fixtures and other equipment	838,097						838,097				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	24,800						24,800				36,900
Accounts receivable related to joint interest owners	1,400						1,400				5,600
Severance tax receivable	4,300						4,300				2,400
Other receivables	4,100						$ 4,100				1,600
Percentage of working interest in wells							100.00%
Total amount of supervision fees charged to wells	1,100			1,200			$ 3,700	3,400
Partial Release of Valuation Allowance		$ 21,200
Income Tax Expense (Benefit)	1,039			220			(19,464)	549
Oil and gas sales	72,014			$ 65,034			218,781	169,134
Trade accounts payable	22,950						22,950				32,683
Accrued operating expenses	3,664						3,664				3,549
Accrued payroll costs	4,079						4,079				4,785
Asset retirement obligation - current portion	307						307				302
Accrued non-income based taxes	4,502						4,502				3,583
Accrued corporate and legal fees	314						314				534
Other payables	3,135						3,135				3,485
Accounts payable and accrued liabilities	$ 38,951						$ 38,951				48,921
Purchase of treasury stock (shares)	411	3,877	11,076	0	4,649	10,458	15,364
Operating Lease, Right-of-Use Asset	$ 10,443						$ 10,443			$ 2,200	$ 0
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
Line of Credit [Member] | New Credit Facility [Member]
Summary of Significant Accounting Policies
Line of Credit Facility, Current Borrowing Capacity												$ 410,000
Oil sales [Member]
Summary of Significant Accounting Policies
Oil and gas sales	28,894			$ 11,124			$ 68,441	32,202
Natural gas sales [Member]
Summary of Significant Accounting Policies
Oil and gas sales	37,051			43,697			131,925	115,833
NGL sales [Member]
Summary of Significant Accounting Policies
Oil and gas sales	6,080			10,213			18,400	21,113
Other sales [Member]
Summary of Significant Accounting Policies
Oil and gas sales	$ (11)			$ 0			$ 16	$ (14)
Subsequent Event [Member] | Line of Credit [Member] | New Credit Facility [Member]
Summary of Significant Accounting Policies
Line of Credit Facility, Current Borrowing Capacity									$ 400,000