Revenue Recognition (Disaggregation) (Details) - USD ($) $ in Thousands	3 Months Ended
	Mar. 31, 2019	Mar. 31, 2018
Disaggregation of Revenue [Line Items]
Gathering and transportation lease revenues	$ 16,257	$ 12,318
Total revenues	17,490	18,536
Natural gas sales
Disaggregation of Revenue [Line Items]
Revenues	110	473
Oil sales
Disaggregation of Revenue [Line Items]
Revenues	(739)	3,462
Natural gas liquid product
Disaggregation of Revenue [Line Items]
Revenues	179	595
Gathering and transportation
Disaggregation of Revenue [Line Items]
Revenues	1,683	1,688
Production
Disaggregation of Revenue [Line Items]
Total revenues	(450)	4,530
Production | Natural gas sales
Disaggregation of Revenue [Line Items]
Revenues	110	473
Production | Oil sales
Disaggregation of Revenue [Line Items]
Revenues	(739)	3,462
Production | Natural gas liquid product
Disaggregation of Revenue [Line Items]
Revenues	179	595
Midstream
Disaggregation of Revenue [Line Items]
Gathering and transportation lease revenues	16,257	12,318
Total revenues	17,940	14,006
Midstream | Gathering and transportation
Disaggregation of Revenue [Line Items]
Revenues	$ 1,683	$ 1,688