Reporting Segments (Segment Information) (Details) - USD ($) $ in Thousands	3 Months Ended		6 Months Ended		12 Months Ended
	Jun. 30, 2019	Jun. 30, 2018	Jun. 30, 2019	Jun. 30, 2018	Dec. 31, 2018
Segment operating revenues:
Gathering and transportation lease revenues	$ 15,969	$ 13,168	$ 32,226	$ 25,486
Total revenues	21,855	17,039	39,345	35,575
Segment operating costs:
Lease operating expenses	2,065	2,007	3,780	3,978
Transportation operating expenses	3,048	3,071	5,724	5,918
Production taxes	141	287	324	609
Gain on sale of assets		(2,388)		(2,388)
Depreciation, depletion and amortization	6,174	6,545	12,603	13,173
Asset impairments	0	0	0	0
Accretion expense	126	123	259	249	$ 497
Total operating expenses	15,900	17,911	32,420	36,408
Segment other income (loss)
Earnings (loss) from equity investments	791	3,111	2,233	7,383
Segment operating income	11,092	10,505	18,888	21,419
Production
Segment operating revenues:
Total revenues	4,184	2,210	3,734	6,740
Segment operating costs:
Lease operating expenses	1,688	1,644	3,007	3,396
Production taxes	141	287	324	609
Gain on sale of assets		(2,388)		(2,388)
Depreciation, depletion and amortization	828	1,251	1,923	2,614
Accretion expense	46	49	100	103
Total operating expenses	2,703	843	5,354	4,334
Segment other income (loss)
Segment operating income	1,481	1,367	(1,620)	2,406
Midstream
Segment operating revenues:
Gathering and transportation lease revenues	15,969	13,168	32,226	25,486
Total revenues	17,671	14,829	35,611	28,835
Segment operating costs:
Lease operating expenses	377	363	773	582
Transportation operating expenses	3,048	3,071	5,724	5,918
Depreciation, depletion and amortization	5,346	5,294	10,680	10,559
Accretion expense	80	74	159	146
Total operating expenses	8,851	8,802	17,336	17,205
Segment other income (loss)
Earnings (loss) from equity investments	791	3,111	2,233	7,383
Total segment other income (loss)	791	3,111	2,233	7,383
Segment operating income	9,611	9,138	20,508	19,013
Natural gas sales
Segment operating revenues:
Revenues	256	226	366	699
Natural gas sales | Production
Segment operating revenues:
Revenues	256	226	366	699
Oil sales
Segment operating revenues:
Revenues	3,811	1,584	3,072	5,046
Oil sales | Production
Segment operating revenues:
Revenues	3,811	1,584	3,072	5,046
Natural gas liquid product
Segment operating revenues:
Revenues	117	400	296	995
Natural gas liquid product | Production
Segment operating revenues:
Revenues	117	400	296	995
Gathering and transportation
Segment operating revenues:
Revenues	1,702	1,661	3,385	3,349
Gathering and transportation | Midstream
Segment operating revenues:
Revenues	$ 1,702	$ 1,661	$ 3,385	$ 3,349