Reporting Segments (Segment Information) (Details) - USD ($) $ in Thousands	3 Months Ended		12 Months Ended
	Mar. 31, 2018	Mar. 31, 2017	Dec. 31, 2017
Segment operating revenues:
Gathering and transportation lease revenues	$ 12,318
Total revenues	18,536	$ 25,807
Segment operating costs:
Lease operating expenses	1,971	4,983
Transportation operating expenses	2,847	3,296
Cost of sales		37
Production taxes	322	473
Depreciation, depletion and amortization	6,628	12,181
Asset impairments		4,688
Accretion expense	126	258	$ 773
Total operating expenses	18,497	32,065
Segment other income
Earnings from equity investments	4,272	482
Total segment other income (loss)	4,272	482
Segment operating income	10,914	373
Production
Segment operating revenues:
Total revenues	4,530
Segment operating costs:
Lease operating expenses	1,752	4,724
Cost of sales		37
Production taxes	322	473
Depreciation, depletion and amortization	1,363	3,281
Asset impairments		4,688
Accretion expense	54	192
Segment other income
Earnings from equity investments		(136)
Total segment other income (loss)		(136)
Segment operating income	1,039	1,065
Midstream
Segment operating revenues:
Gathering and transportation lease revenues	12,318
Total revenues	14,006
Segment operating costs:
Lease operating expenses	219	259
Transportation operating expenses	2,847	3,296
Depreciation, depletion and amortization	5,265	8,900
Accretion expense	72	66
Segment other income
Earnings from equity investments	4,272	618
Total segment other income (loss)	4,272	618
Segment operating income	9,875	(692)
Operating Segments
Segment operating revenues:
Total revenues		25,807
Segment operating costs:
Total operating expenses	11,894	25,916
Operating Segments | Production
Segment operating revenues:
Total revenues		14,596
Segment operating costs:
Total operating expenses	3,491	13,395
Operating Segments | Midstream
Segment operating revenues:
Total revenues		11,211
Segment operating costs:
Total operating expenses	8,403	12,521
Natural gas
Segment operating revenues:
Revenue from contracts with customers	473	2,779
Natural gas | Production
Segment operating revenues:
Revenue from contracts with customers	473	2,779
Oil
Segment operating revenues:
Revenue from contracts with customers	3,462	11,350
Oil | Production
Segment operating revenues:
Revenue from contracts with customers	3,462	11,350
Natural gas liquid
Segment operating revenues:
Revenue from contracts with customers	595	467
Natural gas liquid | Production
Segment operating revenues:
Revenue from contracts with customers	595	467
Gathering and transportation
Segment operating revenues:
Revenue from contracts with customers	1,688	11,211
Gathering and transportation | Midstream
Segment operating revenues:
Revenue from contracts with customers	$ 1,688	$ 11,211