Supplemental Oil and Gas Disclosures (Unaudited) (Details) bbl in Thousands, Mcf in Thousands, Boe in Thousands, $ in Thousands	12 Months Ended
	Dec. 31, 2017 USD ($) Boe $ / bbl bbl Mcf	Dec. 31, 2016 USD ($) Boe $ / bbl bbl Mcf	Dec. 31, 2015 USD ($) Boe $ / bbl bbl Mcf
Capitalized costs relating to oil and gas producing activities [Abstract]
Proved oil and gas properties | $	$ 923,237	$ 794,634
Unproved properties | $	0	0
Total | $	923,237	794,634
Accumulated depreciation, depletion, amortization and impairment | $	(706,537)	(680,861)
Net capitalized costs | $	216,700	113,773
Cost incurred in oil and gas property acquisition and development activities [Abstract]
Development costs | $	94,478	18,262	$ 68,631
Exploration costs | $	8,509	12,529	0
Property acquisition costs | $	31,409	0	0
Total | $	134,396	30,791	68,631
Results of operations for oil and gas producing activities [Abstract]
Revenues | $	86,189	56,493	67,002
Production costs | $	(22,425)	(23,659)	(29,753)
Depreciation, depletion, and amortization | $	(25,676)	(22,803)	(38,040)
Proved property impairment | $	0	(67,626)	(128,573)
Results of operations from oil and gas producing activities (excluding corporate overhead and interest costs) | $	$ 38,088	$ (57,595)	$ (129,364)
Depletion per barrel of oil equivalent | $ / bbl	9.52	10.08	17.44
Oil [Member]
Proved developed and undeveloped reserves [Abstract]
Balance	24,209	24,131	29,390
Revisions of previous estimates	783	1,379	(9,485)
Extensions and discoveries	14,533	1,183	5,679
Purchase of minerals in place	8
Sales of minerals in place	(364)	(1,112)	(13)
Production	(1,574)	(1,372)	(1,440)
Balance	37,595	24,209	24,131
Proved Developed Reserves [Abstract]
Proved Developed Reserves	10,820	7,818	10,022
Proved Undeveloped Reserves [Abstract]
Proved Undeveloped Reserves	25,808	16,391	14,109
NGL [Member]
Proved developed and undeveloped reserves [Abstract]
Balance	8,644	6,556	3,708
Revisions of previous estimates	1,269	2,300	(505)
Extensions and discoveries	2,813	157	3,591
Purchase of minerals in place	14
Sales of minerals in place	(289)	(6)	0
Production	(476)	(363)	(238)
Balance	11,975	8,644	6,556
Proved Developed Reserves [Abstract]
Proved Developed Reserves | Mcf	4	3	2
Proved Undeveloped Reserves [Abstract]
Proved Undeveloped Reserves | Mcf	8	6	5
Natural Gas [Member]
Proved developed and undeveloped reserves [Abstract]
Balance | Mcf	70,829	75,027	55,853
Revisions of previous estimates | Mcf	19,311	(1,537)	(8,002)
Extensions and discoveries | Mcf	14,534	1,179	30,372
Purchase of minerals in place | Mcf	1,001
Sales of minerals in place | Mcf	(3,958)	(680)	(181)
Production | Mcf	(3,889)	(3,160)	(3,015)
Balance | Mcf	97,828	70,829	75,027
Proved Developed Reserves [Abstract]
Proved Developed Reserves | Mcf	39,974	27,792	31,298
Proved Undeveloped Reserves [Abstract]
Proved Undeveloped Reserves | Mcf	57,854	43,037	43,729
Oil Equivalents [Member]
Proved developed and undeveloped reserves [Abstract]
Balance | Boe	44,657	43,190	42,406
Extensions and discoveries | Boe	19,768	1,537	14,332
Purchase of minerals in place | Boe	189
Sales of minerals in place | Boe	(1,312)	(1,232)	(43)
Production | Boe	(2,698)	(2,262)	(2,181)
Balance | Boe	65,351	44,657	43,190
Proved Developed Reserves [Abstract]
Proved Developed Reserves | Boe	21,720	15,018	17,194
Proved Undeveloped Reserves [Abstract]
Proved Undeveloped Reserves | Boe	43,631	29,639	25,996