Reporting Segments (Segment Information) (Details) - USD ($) $ in Thousands	3 Months Ended		12 Months Ended
	Mar. 31, 2019	Mar. 31, 2018	Dec. 31, 2018
Segment operating revenues:
Gathering and transportation lease revenues	$ 16,257	$ 12,318
Total revenues	17,490	18,536
Segment operating costs:
Lease operating expenses	1,715	1,971
Transportation operating expenses	2,676	2,847
Production taxes	183	322
Depreciation, depletion and amortization	6,429	6,628
Asset impairments	0	0
Accretion expense	133	126	$ 497
Total operating expenses	16,520	18,497
Segment other income (loss)
Earnings (loss) from equity investments	1,442	4,272
Segment operating income (loss)	7,796	10,914
Production
Segment operating revenues:
Total revenues	(450)	4,530
Segment operating costs:
Lease operating expenses	1,319	1,752
Production taxes	183	322
Depreciation, depletion and amortization	1,095	1,363
Accretion expense	54	54
Total operating expenses	2,651	3,491
Segment other income (loss)
Segment operating income (loss)	(3,101)	1,039
Midstream
Segment operating revenues:
Gathering and transportation lease revenues	16,257	12,318
Total revenues	17,940	14,006
Segment operating costs:
Lease operating expenses	396	219
Transportation operating expenses	2,676	2,847
Depreciation, depletion and amortization	5,334	5,265
Accretion expense	79	72
Total operating expenses	8,485	8,403
Segment other income (loss)
Earnings (loss) from equity investments	1,442	4,272
Total segment other income (loss)	1,442	4,272
Segment operating income (loss)	10,897	9,875
Natural gas sales
Segment operating revenues:
Revenues	110	473
Natural gas sales | Production
Segment operating revenues:
Revenues	110	473
Oil sales
Segment operating revenues:
Revenues	(739)	3,462
Oil sales | Production
Segment operating revenues:
Revenues	(739)	3,462
Natural gas liquid product
Segment operating revenues:
Revenues	179	595
Natural gas liquid product | Production
Segment operating revenues:
Revenues	179	595
Gathering and transportation
Segment operating revenues:
Revenues	1,683	1,688
Gathering and transportation | Midstream
Segment operating revenues:
Revenues	$ 1,683	$ 1,688